Dedicado para todos aquellos que se dedican al servicio de roscado en tubería galvanizado con maquinaría, este archivo les ayudará a mejorar y estandarizar los proceso para evitar la variabilidad de sus trabajos y reducir considerablemente el rechazo por parte de los clientes, muchas gracias al profesor Alan Joshua Coronel que facilitó los conocimientos para llevar a cabo esté proyecto.
TABLE OF CONTENTS
ACKNOWLEDGMENTS
ACKNOWLEDGMENTS
SUMMARY
ABSTRACT
TABLE OF CONTENTS
LIST OF TABLES
LIST OF ILLUSTRATIONS
TIMELINE OF ACTIVITIES
INTRODUCTION
CHAPTER I. RESEARCH FOUNDATIONS
1.1 Problem Statement
1.2 Research Questions
1.3 Hypothesis
Null Hypothesis (Ho)
Alternative hypothesis (H1)
1.4 Study Variables
1.4.1 Dependent variable
1.4.2 Independent Variable
1.5 Justification
1.6 General Objective
1.6.1 Specific Objectives
CHAPTER II. THEORETICAL FRAMEWORK
2.1 Background
2.2 Theoretical Foundations
2.3 Conceptualization
2.4 State of the Art
2.5 Key practices on the topic
2.6 Findings from empirical research similar to those in this case study
2.7 Standardization
2.8 General considerations of the chapter
CHAPTER III. CONTEXTUAL FRAMEWORK
3.1 International
3.2 National (Mexico)
3.3 Regional (Bajío: Querétaro, Guanajuato, San Luis Potosí, Aguascalientes, Jalisco, Zacatecas)
3.4 Local (Aguascalientes)
3.5 Specific Case Study (GONDEL S.A. de C.V., RIDGID 1224 Machine)
CHAPTER IV. METHODOLOGY
4.1 Type of research
4.2 Population
4.3 Sample
4.3.1 Operators (census)
4.3.2 Sample for SPC by attributes (p-chart and np-chart)
4.4 Assessment tool
4.4.1 Instrument 1: Diagnostic survey (Google Forms)
4.4.2 Tool 2: Poka-yoke checklist (“pre-threading”)
4.4.3 Tool 3: Attribute-based SPC chart
4.4.4 Tool 4: Comb and Adjustment Log
4.5 Data Collection Procedures
4.5.1 Planning and Permits
4.5.2 Instrument Preparation (Google Forms) and Standardization
4.5.3 Baseline survey (before)
4.5.4 Implementation of improvements (Kaizen + Poka-Yoke)
4.5.5 Pilot and comparison (after)
4.6 Complete project planning by phases
CHAPTER V. RESULTS
5.1 Interpretation of results
5.1.2 . How often do you lubricate the machine?
5.1.3 Have you received formal (documented) training to operate the RIDGID 1224?
5.1.4 “I know the settings needed to produce consistent threads in 1/2” and 3/4””
5.1.6 What situations cause you to lose time during the process?
5.1.7 How often do you check the condition/edge of the dies?
5.1.8 What defects are most common when there are friction or temperature issues?
5.1.9. Currently, how do you decide if a thread “passes”?
5.1.10. “What needs to change to reduce defects and rework?”
5.1.11. “Common mistake and how to avoid it”
CHAPTER VI. CONCLUSIONS
6.1 Research Findings: Was the overall research objective achieved?
6.2 Research Findings: Were the specific research objectives met?
6.2.1 Specific Objective 1: Measure and record critical variables of the threading process
6.2.2 Specific Objective 2: Create SPC charts (X-R, histograms, Pareto charts) to evaluate process stability
6.2.3 Specific Objective 3: Identify root causes using the Ishikawa diagram and
the 5 Whys
6.2.4 Specific Objective 4: Propose corrective actions related to lubrication, wear, and operating parameters
6.2.5 Specific Objective 5: Validate the improvement by comparing before and
after the process
6.3 Hypothesis: Which one was met? Justification regardless of the answer
6.4 International support for the results of the diagnosis and pilot study
6.4.1 Purpose of the document
6.4.2 Key findings of the study (summary)
6.4.3 International evidence supporting each finding
6.4.4 Summary matrix: finding and international support
6.5 International critiques (negative comments) relevant to the research results
CHAPTER VII. RECOMMENDATIONS
7.1 Consolidate the Statistical Process Control (SPC) system by attributes
7.2 Rigorous standardization of lubrication
7.3 Standardize staff training and consolidate a Standard Operating Procedure (SOP)
7.4 Maintain the pre-threading checklist and the Poka-Yoke for minimum distance between the head and the press
7.5 Formal logbook for combs and spindle adjustments
7.6 Formal response plan for increases in non-conformities
7.7 Systematic tracking of cycle times by batch and by operator
7.8 Clear guidelines and layout improvements
7.9 documentation, traceability, and the sustainability of improvements
LIST OF TABLES
Table 1. Schedule of activities
Table 2. Percentage of nonconformities per batch (SPC pilot by attributes)
Table 3. Matrix of international support findings
Table 4. Matrix of negative comments with international support
LIST OF ILLUSTRATIONS
Illustration 1. Chart “How often do you lubricate the machine?”
Figure 2. Graph: “Have you received formal (documented) training to operate the RIDGID 1224?”
Illustration 3. Chart: “I know the settings needed to produce consistent threads in 1/2” and 3/4””
Figure 4. Chart: “List the steps for cutting a thread from 1 to 6”
Figure 5. Chart: What situations cause you to waste time during the process?
Figure 6. Chart: How often do you check the condition/edge of the combs?
Figure 7. Chart: Which defects occur most frequently when there are friction/temperature issues?
Figure 8. Chart: How do you currently decide if a thread “passes”?
Figure 9. GOOD THREAD AND WORN THREAD
Figure 10. GOOD THREAD AND BURNED THREAD
Figure 11. WEARED PIPE
Figure 12. BATCH 1
Figure 13. LOT 2
Figure 14. LOT 3
Figure 15. LOTS
Figure 16. Project Planning
Figure 17. RIDGID 1224 Machine
Figure 18. General laborer Eduardo Espinoza
DEDICATIONS
I dedicate this research project, first and foremost, to my parents, Juan González Flores and Leticia Herrera Monsivaís, who have been the most important pillar in my life and in my personal and academic development. Thank you for your love, for your constant effort, for the values you have instilled in me, and for always offering me your unconditional support at every stage of my journey. This achievement also belongs to you, because without your trust, sacrifice, and daily encouragement, it would not have been possible to get this far.
In a very special way, I dedicate this work to my fiancée, Fernanda Galilea Ortíz Molinero, for accompanying me through this process with love, patience, understanding, and strength. Her presence in my life has been a constant source of motivation to keep moving forward, even in the most challenging moments. Thank you for encouraging me to grow, for believing in me, and for being there every step of the way toward this goal.
I also dedicate this project to my siblings, Indra González Herrera and Santiago González Herrera, who are an essential part of my life. Thank you for your affection, your companionship, your words of encouragement, and for always reminding me of the importance of pushing myself and continuing to fight for my goals.
I also dedicate this achievement to my pets: Poison, Cookie, Jesse, Pancho, Garrik, Korbach, Bella, and Freddie, who in a very special way have filled my days with joy, companionship, and peace of mind. Although they don’t express it in words, they have been part of my journey and of the moments when I most needed peace and motivation.
I thank and dedicate this work to the Technological Institute of Aguascalientes, for giving me the opportunity to pursue professional training, for opening the doors to knowledge, and for providing me with the necessary tools to develop as a future professional.
Finally, I dedicate this project to Professor Alan Joshua Coronel Medina, for his guidance, his academic commitment, his willingness to mentor this work, and for contributing valuable insights that made the development of this research possible.
ACKNOWLEDGMENTS
I am deeply grateful to the Technological Institute of Aguascalientes for being the place where I have strengthened my knowledge, skills, and professional vision. This institution has been a fundamental foundation in my academic training and in the development of competencies that today allow me to successfully complete this project.
I express my most sincere gratitude to Professor Alan Joshua Coronel Medina for his support, guidance, and mentorship throughout the course of this research. His willingness to answer questions, his experience, and his commitment to the education of his students were essential in providing structure, direction, and substance to this work.
I thank the company GONDEL S.A. de C.V. for the opportunity to conduct this research within its facilities, as well as for the trust placed in me to analyze a real-world situation involving the threading process with the RIDGID 1224 machine. The openness to observe, record, and understand the operational process made it possible for this research to have a practical and applied focus.
I, Juan Edén González Herrera, thank myself for the effort, discipline, time, perseverance, and dedication invested throughout this process. I acknowledge the commitment required to balance personal, academic, and professional responsibilities to complete this research, as well as the perseverance needed to transform a real operational problem into a documented and substantiated improvement proposal. The project involved not only diagnosing process variability but also structuring a pilot study of 200 1/2” NPT threads with attribute monitoring and a before-and-after comparison to demonstrate improvements.
Finally, I thank everyone who, directly or indirectly, contributed their support, experience, trust, and willingness to see this project through to completion. Every contribution was valuable in building a project with academic, technical, and human significance.
ABSTRACT
The objective of this research was to implement a Statistical Process Control (SPC) system on the RIDGID 1224 threading machine at GONDEL S.A. de C.V., with the aim of reducing process variability and lowering the percentage of rejected threads. The study arose from the presence of recurring defects in NPT threads, such as worn threads, burnt threads, and cracks, which led to rework, wasted time, and impacts on service quality.
The methodology was developed using an applied, pre-experimental before-and-after approach. Due to the absence of GO/NO-GO gauges, control was implemented by attributes through standardized visual inspection and a “pass/fail” functional test. As part of the study, a pilot test was conducted with 200 1/2” NPT threads, distributed across four lots of 50 pieces, using an NP chart to monitor nonconformities. The results showed that, by standardizing the minimum distance between the head and the press at > 7.5 cm, the “worn thread” defect ceased to occur and the percentage of nonconformities was reduced from 20% to 10%.
It is concluded that the application of attribute-based SPC, complemented by Kaizen and Poka-Yoke actions, constitutes a viable alternative for improving process stability, reducing rejects, and strengthening the workshop’s operational reliability.
ABSTRACT
This research aimed to implement a Statistical Process Control (SPC) system on the RIDGID 1224 threading machine at GONDEL S.A. de C.V., in order to reduce process variability and decrease the percentage of rejected threads. The study was motivated by recurring NPT thread defects such as worn threads, burned threads, and cracks, which caused rework, time losses, and quality problems.
The methodology followed an applied, pre-experimental before/after approach. Since GO/NO-GO gauges were not available, control was carried out by attributes using standardized visual inspection and functional pass/fail testing. A pilot test of 200 NPT 1/2” threads was conducted in four lots of 50 pieces, using an np chart to monitor nonconforming units. Results showed that after standardizing the minimum distance between the die head and the vise to > 7.5 cm, the “worn thread” defect disappeared and the nonconforming rate decreased from 20% to 10%.
It is concluded that attribute-based SPC, together with Kaizen and Poka-Yoke actions, is a feasible alternative to improve process stability, reduce rejections, and strengthen the operational reliability of the workshop.
SCHEDULE OF ACTIVITIES
Illustrations are not included in the reading sample
Table 1. Activity Schedule
Source: Prepared by the author (2026)
INTRODUCTION
The project we are developing aims to improve the quality and consistency of the threads produced by the RIDGID 1224 threading machine. Throughout the process, we have identified that one of the main problems is the variability in results: some threads come out well, others require rework, and sometimes rejects are generated that affect delivery times and customer satisfaction. After analyzing the process using tools such as the Ishikawa diagram, it became clear that the most significant causes are related to day-to-day operations: staff training, the operator’s movements, the organization of the work area, and the lack of a standardized method to ensure that everyone follows the same steps.
Based on this, the project focuses on three main areas. The first is the application of SPC (Statistical Process Control), which will allow us to better understand how the process behaves, when variability occurs, and how stable the threads produced are. The second line is the Kaizen philosophy, which helps us gradually improve the way we work by eliminating unnecessary movements, reducing downtime, and making the process more fluid. The third is the use of Poka-Yoke, which involves implementing small solutions to prevent human errors, especially in repetitive tasks such as threading.
To organize the work, a clear structure of roles was defined: Project Director, Supervisor, Lead Operator, and Operator. Each has specific activities ranging from analyzing data and validating improvements to documenting the process, training staff, and ensuring that changes are actually implemented. This structure was formalized in a WBS (Work Breakdown Structure), which has helped us allocate responsibilities and move forward in an orderly manner.
In addition, a twelve-week schedule was developed that outlines the activities from the initial analysis through the implementation of improvements and the evaluation of results. This schedule was also adapted for the Supply Chain Management course, since improvements in the threading process impact not only quality but also delivery times, workflow, and the workshop’s overall efficiency.
Overall, the project aims not only to correct current problems but also to lay a solid foundation so that the process becomes more stable, faster, and easier to control. The idea is that the improvements should not depend on any one individual but rather be integrated into the workshop’s standard operating procedures.
CHAPTER I. RESEARCH BACKGROUND
1.1 Problem Statement
Variations affecting the quality of NPT threads have been identified in the industrial pipe threading process using the RIDGID 1224 machine. Among the most frequent defects are visually “burnt” threads, cracks, depths outside specification, and connections that are too loose or excessively tight. These defects result in customer rejections, rework, wasted time, and additional costs.
Probable causes include overheating of the dies due to prolonged workloads, uneven tool wear, variation in lubricant use, and lack of control over critical process parameters. Currently, there is no formal monitoring system in place to identify, measure, and control process variability. Therefore, it is considered necessary to implement Statistical Process Control (SPC) to stabilize the process and reduce rejections.
1.2 Research Questions
What factors are causing variability in the NPT and BSP threads produced by the RIDGID 1224 machine?
How do comb wear and temperature affect thread quality?
What is the current level of process variability, and how many rejects does it generate? Can Statistical Process Control (SPC) reduce variability and improve threading quality? What quality tools can be used to identify the root causes of defects?
1.3 Hypotheses
Null hypothesis (Ho)
Ho: The implementation of Statistical Process Control (SPC) does not reduce the variability of the threading process or decrease the percentage of rejected NPT and BSP threads.
Alternative hypothesis (H1)
H1: The implementation of Statistical Process Control (SPC) does reduce the variability of the threading process and decreases the percentage of rejected NPT and BSP threads.
1.4 Study Variables
1.4.1 Dependent variable
Quality of NPT and BSP threads, measured by:
- Percentage of rejected parts.
- Dimensional compliance (pass/fail).
- Surface finish.
1.4.2 Independent variable
Statistical Process Control (SPC) applied to threading, including:
- Dimension monitoring.
- Temperature and lubrication control.
- Condition and wear of the dies.
- Data recording and analysis using X-R charts, histograms, and Pareto charts.
1.5 Justification
The quality of threads is essential to ensure tightness and safety in industrial systems. Current defects lead to financial losses, customer dissatisfaction, and rework that affects productivity. Implementing SPC will allow us to:
- Reduce process variability.
- Identify root causes using tools such as Ishikawa and Pareto.
- Establish control limits and continuous monitoring.
- Improve the visual and dimensional quality of threads.
- Reduce rejects and associated costs.
Furthermore, the project is feasible because it requires a small team, basic measuring tools, and accessible statistical analysis. Its impact is significant for both operations and customer satisfaction.
1.6 Overall Objective
Implement a Statistical Process Control (SPC) system in the industrial pipe threading operation using the RIDGID 1224 machine to reduce process variability and lower the percentage of rejected NPT and BSP threads.
1.6.1 Specific Objectives
- Measure and record critical variables of the threading process.
- Create SPC charts (X-R, histograms, Pareto charts) to evaluate process stability.
- Identify root causes using the Ishikawa diagram and the 5 Whys method.
- Propose corrective actions related to lubrication, wear, and operating parameters.
- Validate the improvement by comparing before and after the process.
CHAPTER II. THEORETICAL FRAMEWORK
2.1 Background
Variations have been identified in the threading process using the RIDGID 1224 machine that affect the quality of NPT threads, resulting in rejects and rework that impact productivity and customer satisfaction. These variations are primarily related to die wear, a lack of standardization in operations, and insufficient control of parameters such as temperature and lubrication. Given this problem, there is a need to implement a Statistical Process Control (SPC) system that allows for measuring, analyzing, and stabilizing the process, thereby reducing defects and increasing reliability in the supply chain.
Statistical Process Control (SPC) has been applied in multiple industries to reduce variability and improve quality. In machining processes, it has been demonstrated that a lack of monitoring leads to recurring defects and high rework costs. According to López- Morales et al. (2021), the implementation of SPC in cutting and threading operations reduced rejects in metal parts by up to 30%, demonstrating the importance of having a formal control system. Likewise, recent research highlights that variability in manual processes is directly related to tool wear and a lack of standardization (García & Torres, 2022).
2.2 Theoretical Foundations
SPC is based on Shewhart’s theory of common and special variation, and on the use of control charts to identify significant deviations. Current studies indicate that X"-R charts remain useful in industrial processes, especially when combined with Pareto and Ishikawa analyses to identify root causes (Martínez et al., 2020). Furthermore, the Kaizen philosophy and Poka-Yoke systems complement SPC by focusing on error prevention and continuous improvement (Hernández & Cruz, 2021).
X-R Chart (what the chart consists of, types of charts, and characteristics of the chart type)
Kaizen (what the chart consists of, types of charts, and characteristics of the chart type)
Poka-Yoke (what the chart consists of, types of charts, and characteristics of the chart type)
Pareto Chart (what the chart consists of, types of charts, and characteristics of the chart type)
Ishikawa (what the chart consists of, types of charts, and characteristics of the chart type)
2.3 Conceptualization
In the context of supply chain management, SPC is not only a control tool but also a strategic mechanism that allows for identifying variations, reducing waste, and ensuring customer satisfaction. Its application in industrial pipe threading with the RIDGID 1224 machine involves recognizing that variability is not solely a technical phenomenon, but also an organizational one: it depends on factors such as tool wear, staff training, standardization of movements, and preventive maintenance.
SPC: a set of statistical techniques for monitoring and controlling processes, such as the Exponential Weighted Moving Average (EWMA)
Variability: fluctuations in critical parameters such as cracks, diameter, thread pitch, surface finish, burn marks, and thread depth.
Kaizen: continuous improvement through the standardization of movements to reduce lead time.
Poka-Yoke: simple mechanisms to prevent human errors and ensure the overall safety of machine operators.
These definitions help define the scope of the project and link it to supply chain management, where quality is a key factor in competitiveness (Rodríguez, 2022).
2.4 State of the Art
Studies in machining and metalworking shops highlight that tool wear and a lack of standardization are the main causes of scrap, and that the application of control charts and root cause analysis succeeds in reducing defects and improving productivity, which supports their relevance in the case of the RIDGID 1224 machine.
Recent literature shows successful applications of SPC in advanced manufacturing. Zhang et al. (2021) report that the integration of SPC with predictive maintenance reduced defects by 40% in machining processes. In Latin America, Ramírez & Salinas (2020) demonstrate that the application of SPC in metalworking shops improves reliability and customer satisfaction.
Illustrations are not included in the reading sample
Table: State of the Art Source: Prepared by the author (2026)
2.5 Key practices on the topic
The most effective practices for reducing variability in manufacturing processes include clearly defining critical variables, periodically calibrating measuring instruments, recording tool service life, and applying methodologies such as Kaizen and Poka-Yoke. These actions enable the standardization of movements, prevent errors, and maintain reliable statistical control, which translates into a reduction in rejects and an improvement in product quality.
The most relevant practices include:
- Defining critical variables and sampling plans.
- Calibrating measuring instruments.
- Documenting tool service life.
- Applying Kaizen to standardize movements.
- Implementing Poka-Yoke to prevent errors.
These practices have been validated in recent empirical studies (Hernández et al., 2022; Pérez & Gómez, 2021).
2.6 Empirical research findings similar to those in this case study
Research on machining processes shows that 3- to 6-month SPC pilot studies allow for the establishment of reliable control limits and a reduction in rejects of 20-50% (Li et al., 2020). In Mexico, case studies in metalworking shops report significant improvements in productivity and quality after applying SPC alongside operational training (Ramírez, 2021).
2.7 Standardization
Implementation must align with ISO 9001:2015 standards on quality management and with industrial metrology guidelines. According to the International Organization for Standardization (ISO, 2020), documentation and traceability are essential to ensure the sustainability of SPC. This involves developing manuals, control forms, and records that enable internal and external audits.
In addition to the ISO 9001:2015 standard on quality management, it is relevant to consider the ISO 14001:2015 standard on environmental management, since the threading process involves the use of lubricants and the generation of metal waste that must be managed responsibly. Incorporating this standard ensures that quality improvements not only reduce variability and rejects but are also carried out within a framework of environmental sustainability.
2.8 General considerations of the chapter
The theoretical framework confirms that SPC is a viable and effective tool for reducing variability in threading processes. The combination of statistical monitoring, standardization of movements, and error prevention ensures a positive impact on quality and customer satisfaction. Furthermore, empirical evidence supports the relevance of implementing an SPC pilot in the workshop, with expected results of reduced rejects and improved reliability.
CHAPTER III. CONTEXTUAL FRAMEWORK
This chapter describes the business context of the pipe threading service and related activities—threading, cutting, manufacturing, and metal pipe (galvanized, steel, black pipe, etc.)—from the international to the local level, to situate the specific case of GONDEL S.A. de C.V. in Aguascalientes with the RIDGID 1224 threading machine.
3.1 International
Internationally, pipe threading is typically part of “pipe fabrication” services (manufacturing and preparation of pipes), which include processes such as cutting, threading, and grooving. A leading example is Ferguson, which offers pipe fabrication and end preparation services, including cutting, threading, and grooving, depending on regional availability. (Ferguson, n.d.).
In specialized markets such as energy (oil & gas), threading is treated as a critical process for the integrity of the connection; for example, K&B Industries states that it provides Tubular Threading Services and machining/manufacturing capabilities. (K&B Industries, n.d.).
Another international model combines threading with inspection and repair to extend the service life of the material; Inter-Mountain describes inspection services that include thread repair. (Inter-Mountain Pipe & Threading, n.d.).
Finally, there are companies that offer threading and grooving services for pipes of various materials and sizes, such as Pevegal, which presents its threading and grooving service for pipe preparation. (Pevegal, n.d.).
Table 3.1. International industry leaders (threading/slotting/pipe manufacturing)
Illustrations are not included in the reading sample
Source: Prepared by the author (2026).
3.2 Domestic (Mexico)
In Mexico, pipe threading is offered both as a standalone service and as part of integrated industrial solutions (manufacturing, commissioning, and pipe installation). This framework includes Mexican companies with published services or a stated national scope.
Tubos y Conexiones advertises steel pipe threading services with NPT tapered or NPS straight threads, in addition to integrated processes (de-burring and chamfering), representing a “full-service” model. (Tubos y Conexiones, n.d.).
Grupo Mafameb advertises pipe threading services (NPT) with explicit ranges, serving as an example of a formal technical offering. (Roscados de Querétaro/Grupo Mafameb, n.d.).
Lapyma offers CNC steel threading and serves “Querétaro and all of Mexico,” making it a national benchmark in terms of scope. (Lapyma, n.d.).
3FAMBAL offers industrial piping solutions (assembly/manufacturing) and includes threaded piping among its applications, demonstrating that threading is often integrated into comprehensive industrial services. (3FAMBAL, n.d.).
Table 3.2. Leading Companies in Mexico (threading services and/or comprehensive piping solutions)
Illustrations are not included in the reading sample
Source: Prepared by the author (2026).
3.3 Regional (Bajío: Qro, Gto, SLP, Ags, Jal, Zac)
In the Bajío region, industrial and construction demand has led to a regional supply of companies that meet piping needs (fluid conveyance, gas, fire protection, air, and water), where threading is offered as a standalone service or as a process integrated into industrial manufacturing/service.
Regional examples with explicit or integrated threading include: Servigas de León (Guanajuato), which mentions pipe threading as part of its offerings of fittings and piping for water and gas; and Servicio de Torno Reynoso (Guadalajara, Jalisco), which lists pipe threading and complementary services (sheet metal work, cutting, and machining). (Servigas de León, n.d.; Servicio de Torno Reynoso, n.d.).
Table 3.3. Regional examples (Bajío) of companies offering threading and/or piping
Illustrations are not included in the reading sample
Source: Compiled by the author (2026).
3.4 Local (Aguascalientes)
Locally in Aguascalientes, the market for metal pipes and supplies consists of companies that manufacture or sell pipes (carbon steel, galvanized, etc.) and/or related materials. For the purposes of this project, two local companies are considered.
CIASA describes itself as a company specializing in the manufacture of carbon steel tanks and pipes in Aguascalientes, which places it within the metal pipe sector. (CIASA, n.d.; CIASA Tanks, n.d.).
Plásticos Russell is included as a local reference in the field of pipes and fittings (primarily PVC and related components), with a physical presence and official website, which is useful for contextualizing the local availability of materials and supplies. (Plásticos Russell, n.d.; Infoisinfo, n.d.).
Table 3.4. Local (Aguascalientes) (Aguascalientes) related with piping and supplies.
Illustrations are not included in the reading sample
Source: Prepared by the author (2026).
3.5 Specific case study (GONDEL S.A. de C.V., RIDGID 1224 machine)
The case study takes place in the industrial workshop of GONDEL S.A. de C.V., where galvanized pipe threading services are provided using the RIDGID 1224 threading machine, with the aim of reducing variability and scrap rates through SPC (statistical process control), Kaizen, and Poka-yoke methodologies.
The RIDGID 1224 is designed to thread various materials (black pipe, galvanized pipe, steel, etc.) and allows for NPT threading with heads covering ranges from %” to 4”; constant lubrication is recommended to ensure threading quality.
In the project, due to the current limitation of not having NPT GO/NO-GO gauges, it is proposed to initiate SPC by attributes, using standardized visual inspection and functional testing with standard galvanized connections (pass/fail), with the possibility of evolving to variables if gauges are incorporated.
The diagnostic survey administered to operators highlights relevant human factors: areas for improvement reported include “maintaining concentration,” “adjusting the die properly,” and “constantly checking dies,” while frequent errors include “using the phone while operating/working” and practices that hinder movement (crossing hands).
A pilot study was conducted with 200 1/2” NPT threads distributed across 4 lots of 50 pieces, keeping n constant, which allowed the use of an NP chart to monitor the number of nonconformities per lot.
During the pilot, a special cause was identified in batch 1 (“worn thread” defect due to insufficient distance between the head and the press), which was eliminated by standardizing a minimum distance of > 7.5 cm, with no recurrence in batches 2-4, validating a simple and effective Poka-Yoke.
Likewise, a thermal pattern was detected toward the end of the batches (“burnt” threads and cracks), which supports the need for operational control (breaks, lubrication, comb inspection) and preventive maintenance as part of process stabilization.
The Kaizen component is justified by the significant variation in productivity among operators (55-60 min per batch vs. 100 min per batch), which directly impacts delivery times; therefore, standardizing methods and training using SOPs and checklists is proposed.
Finally, the case incorporates the safety and order framework through applicable STPS regulations (machinery safety, PPE, order and cleanliness, material handling, and a preventive approach), which is also related to quality and risk reduction during the threading operation.
CHAPTER IV. METHODOLOGY
The objective of this chapter is to define the method for assessing the current situation and evaluating the impact of statistical process control (SPC), the Kaizen methodology, and Poka-yoke on %” and %” NPT threads, using tools (survey, checklist, and SPC forms) as well as a before/after data collection plan.
4.1 Type of research.
The research is applied because it seeks to solve a real operational problem (variability and rejects in NPT threading) by creating a control and standardization system that can be implemented in the workshop.
The approach is quantitative with qualitative support:
Quantitative: through measurement of process indicators (percentage of nonconformities, rework, cycle times) and SPC analysis by attributes.
Qualitative: through operator perception (surveys and observation), to explain variation by method and support the adoption of Kaizen/Poka-Yoke.
The design is field-based (data from actual operations), longitudinal (monitoring over weeks), and a pre-experimental before/after design without a control group, because the process being studied is the same and results are compared after improvements are implemented.
4.2 Population.
1. Operator population: all operators who operate the RIDGID 1224 during the shift (shop floor operation).
2. Production population: all galvanized threaded pipe parts produced during the study period, limited to 1/2” and 3/4” NPT (scope of the project).
3. Process event population: all threading operations (head adjustment changes, die changes, lubrication, etc.) that occur during the diagnostic and pilot periods.
4.3 Sample.
Human sample (census): a census of the shift operators involved in the process is considered, since the number of participants is small and variation by operator is a key factor in the project (differences in time and operating practices).
Product sample (SPC pilot): a pilot study was conducted with 200 1/2” threads on galvanized pipe, organized into 4 lots of 50 pieces, maintaining a constant sample size of n=50 per lot. This structure allows for the application of an np chart to monitor the number of nonconformities (d) per lot, which is appropriate when the sample size is fixed. The nonconformity data per batch from the pilot were d = [10, 5, 5, 5], where batch 1 reflects a special cause that was subsequently eliminated.
4.3.1 Operators (census)
We will work with a census of shift operators (all those who operate the machine), since the team is small and variation by method/operator is critical.
4.3.2 Sample for Attribute SPC (p-chart and np-chart)
Since the workshop does not currently have NPT dimensional gauges (GO/NO-GO), SPC is implemented by attributes (Conforming/Nonconforming).
- Unit of analysis: threaded part evaluated as “Pass/Fail” by visual inspection + fit test with a standard connection.
- Recommended sampling: by batch/work order, recording size (1/2” or 3/4”), operator, pass/fail result, and dominant defect.
- Sample size per point: (reasonable suggestion) n=10-20 pieces per size per day or per order, depending on volume; if the batch is small, 100% inspection. (This should be adjusted based on your actual volume)
4.4 Evaluation tool.
The main tool will be a Google Forms questionnaire with a Likert scale, plus operational tools for SPC and Kaizen/Poka-yoke
4.4.1 Tool 1: Diagnostic survey (Google Forms)
- Targeted at RIDGID 1224 operators
- Sections: profile, technical knowledge, operating practices, inspection, and adoption of SPC/Kaizen/Poka-yoke.
- Scales: Likert 1-5 and frequency: (Never, once a month, once a week, after each workday, and after each thread).
Evidence: The survey, which has already been administered, reveals findings such as distraction due to cell phone use and the need to improve head adjustment and comb inspection.
4.4.2 Tool 2: Poka-yoke “Pre-Threading” Checklist
Pre-threading checklist (lubrication, head adjustment, comb condition, deburring, part alignment) to prevent low-cost omissions and facilitate easy adoption.
4.4.3 Tool 3: Attribute-based SPC chart
Record by order/batch:
- size (1/2”, 3/4”), operator, number inspected (n), number non-conforming (d), type of defect (crack, burn, loose/tight fit), corrective action.
4.4.4 Tool 4: Comb and Adjustment Log
Record of comb changes and head adjustments, to correlate defects with wear and configuration.
4.5 Data Collection Procedures
Using your colleague’s “planning → implementation → processing” methodological framework as a reference, a 5-phase procedure is proposed (diagnosis and baseline → SPC design → Kaizen/Poka-Yoke → pilot → comparison).
The following tools are used:
Operational defect catalog (acceptance/rejection criteria): to reduce subjectivity in inspection, defects were defined using closed criteria:
- Alignment (Fail): fails the manual functional test.
- Burn (FAIL): excessive burn not accepted.
- Burn + crack (FAIL): direct rejection.
- Burn (pass): warning condition (early sign) for monitoring.
CTQ (Critical to Quality):
- CTQ-1: functional compliance via mating test (pass/fail).
- CTQ-2: visual condition (“burn” passes) as a preventive indicator.
SPC charts by attributes: recording by batch/shift (n, d, defect classification, operator, corrective actions) and preparation of NP/P charts as appropriate.
Poka-Yoke checklist and logs: mandatory pre-verification (lubrication, minimum distance >7.5 cm, comb condition, cleaning to prevent slippage) and recording of comb changes/adjustments, for traceability and prevention of repetitive errors.
4.5.1 Planning and Permits
- Scope definition: NPT threading on 1/2” and 3/4” galvanized pipe.
- Internal authorization to conduct a survey and use process records.
- Definition of acceptance/rejection criteria by attributes (visual + pattern fit).
4.5.2 Instrument preparation (Google Forms) and standardization
- Form configuration with sections, mandatory questions, and Likert scales.
- Standardization of “reference connections” for functional testing (PAT-12 and PAT-34) as a temporary substitute for NPT gauges.
4.5.3 Baseline survey (before)
- Administer diagnostic survey to operators.
- Record by order/batch: n inspected, d non-conforming, defect type, operator.
- Measure cycle times (Kaizen): time per part or order (stopwatch).
(appears as a recommendation in open-ended responses)
4.5.4 Implementation of improvements (Kaizen + Poka-Yoke)
- Design SOPs (standard operating procedures) and train on the correct sequence. - Implement a Poka-Yoke checklist and head adjustment markings.
4.5.5 Pilot study and comparison (after)
- Repeat the SPC chart by attributes and compare “before vs. after” for:
- % of nonconformities by size (1/2”, 3/4”)
- dominant defects (Pareto)
- cycle times and rework
- compliance with checklists and SOPs (standard operating procedures)
4.6 Complete project planning by phases.
Phase 1: SPC pilot by attributes (execution with constant n)
- Pilot production and evaluation: 4 lots of 50 pieces (n=50) for a total of 200 threads.
- Attribute inspection: manual functional test + visual inspection, recording “pass/fail” and defect type.
- Construction of an np chart with d per batch; identification of special cause (batch 1) and subsequent stability (batches 2-4).
Phase 2: Kaizen Implementation (standard work and reduction of operator variation)
- Document standard operating procedure (SOP) and provide training to reduce time differences between operators (evidence of a gap: 55-60 min vs. 100 min per batch).
- Measure “before vs. after” times per batch to validate improvement.
Phase 3: Poka-Yoke Implementation and Response Plan
Standardized operating parameters:
- lubrication 0.5 L/100 threads,
- break of >1 hour between batches,
- functional test by hand only,
- minimum distance >7.5 cm between head and press.
Poka-Yoke validation: elimination of the “worn thread” defect after applying the minimum distance (not repeated in batches 2-4).
Response plan for increased non-conformities: contain the batch, verify distance, lubrication, and condition of the dies, and validate with 3 consecutive parts before continuing; record corrective action for traceability.
CHAPTER V. RESULTS
To gather information from machine operators regarding the machine’s use, a survey was conducted among the 5 individuals directly involved in threading operations. The results are attached here as feedback and a tool for service improvement.
“Knowledge and Operation Diagnostic Survey - RIDGID 1224 Threading Machine”
The purpose of this survey is to gather information on the level of knowledge and current operating practices regarding the RIDGID 1224 threading machine, focusing on NPT threading of 1/2” and 3/4” galvanized pipe.
The results will be used solely to implement improvements in service quality and processes.
5.1 Interpretation of Results
5.1.2. How often do you lubricate the machine?
Figure 1. Graph: “How often do you lubricate the machine?”
Illustrations are not included in the reading sample
Interpretation: The spread of responses suggests that there is no single standard for lubrication. This is critical because lubrication affects temperature, friction, thread finish, and die life; when everyone lubricates differently, it increases the variability of the results.
Summary: Lubrication is not standardized; this may explain thermal defects, process variation, and the causes of the “burn” and “burn NO PASS” defects.
5.1.3 Have you received formal (documented) training to operate the RIDGID 1224 ?
Figure 2. Chart: Have you received formal (documented) training to operate the RIDGID 1224 ?
Illustrations are not included in the reading sample
Interpretation: The presence of “partial/no” responses indicates that the process has been learned through practice or informal transfer. This typically leads to “personal methods,” variation in settings, and reliance on the most experienced operator.
Summary: Lack of standardized formal training; SOP and documented training are warranted.
5.1.4 “I know the settings required to obtain consistent threads in 1/2” and 3/4””
Figure 3. Graph: “I know the settings required to obtain consistent 1/2” and 3/4” threads”
Illustrations are not included in the reading sample
Interpretation: A perception of medium-to-high proficiency is also observed. While this is positive, the pilot demonstrates that small adjustments (distance, lubrication, combs) do make a difference. Here, it is advisable to convert “perceived knowledge” into “standardized knowledge” (parameters, tolerances, checklists).
Summary: There is confidence in the adjustments, but they need to be formalized into parameters and a checklist to ensure consistency.
1.1.5 “Order the steps for making a thread from 1 to 6”
Figure 4. Chart “List the steps for making a thread from 1 to 6”
Illustrations are not included in the reading sample
Interpretation: This chart reflects each operator’s thought process. When the order differs from person to person, the risk of omitting steps increases (e.g., checking taps, verifying lubrication, cleaning burrs). This explains rework and time variations.
Summary: The method is not 100% standardized; an SOP with a fixed sequence and prior verification is urgently needed.
1.1.6 What situations cause you to lose time during the process?
Figure 5. Chart: What situations cause you to lose time during the process?
Illustrations are not included in the reading sample
Interpretation: The main bottleneck is clearly evident here: readjusting the head is the dominant time waster. Second is changing combs without having them ready; followed by hesitation/repeated inspection and waiting for material. This connects directly to Kaizen actions: advance preparation, comb kit, standard head parameters, and a response plan.
Summary: The greatest waste of time comes from head adjustment and the lack of preparation of combs/tools.
5.1.7 How often do you check the condition/sharpness of the combs?
Figure 6. Chart: How often do you check the condition/edge of the combs?
Illustrations are not included in the reading sample
Interpretation: The way the graph is structured (frequency scale) indicates that this practice is not entirely consistent. When comb checks are sporadic, the likelihood of burnt threads, burrs, or inconsistent fit increases. This is corrected with a standard: “check at the start of the shift + every X parts + visual inspection.”
Summary: Comb inspection requires a standard frequency and criteria to prevent defects.
5.1.8 What defects appear most when there problems r friction/temperature issues?
Figure 7. Graph: Which defects appear most frequently when there are friction/temperature- s?
Illustrations are not included in the reading sample
Interpretation: The graph indicates that the defect most associated with friction/temperature is a burnt thread, followed by others such as cracks/microcracks, burrs, and inconsistent fit. This aligns with the finding of a “thermal pattern” by batch. The action here is to control lubrication, pauses, and comb life.
Summary: Friction/temperature mainly results in “burnt threads”; control efforts should focus on lubrication and combs.
5.1.9. Currently, how do you decide if a thread “passes”?
Figure 8. Chart: How do you currently decide if a thread “passes”?
Illustrations are not included in the reading sample
5.1.10. “What needs to change to reduce defects and rework?”
What do you think is the most important thing that needs to change to reduce defects and rework?
5 answers
Listen carefully to instructions Stay
focused Adjust the head properly
Check the dies constantly Time the
process with a stopwatch
Interpretation: The answers focus on human and method-related factors: concentration, head adjustment, constant comb checks, and time measurement. This aligns with the SPC + Kaizen + Poka-Yoke approach: standardize, measure, and control.
Summary: The expected improvement focuses on method and operational discipline: proper adjustment, comb checks, and measurement.
5.1.11. “Common Mistake and How to Avoid It”
Describe a common mistake you’ve seen when operating the RIDGID 1224 and how you would avoid it
5 answers
Using your cell phone too much
Having the pipe to be threaded far from the machine, as it affects completion time
Using the phone while operating
Using your phone while working
Crossing your arms while using the machine hinders movement
Interpretation: The pattern of cell phone distraction and improper postures/movements (“crossing your hands”) is repeated, in addition to setup issues (“tube too far away”). This is ideal for a behavioral Poka-Yoke: visible “no cell phones” rule, nearby part layout, and safe hand sequence.
Summary: Common errors involve discipline and ergonomics; they can be prevented with visual rules, layout, and checklists.
Demonstrated project improvement.
After implementing the Poka-Yoke (distance >7.5 cm), the special cause “worn thread” was eliminated, and the non-conformance rate dropped from 20% to 10% starting with batch 2.
For the purposes of the pilot, “before” corresponds to batch 1 prior to standardizing the head-to-press distance, and “after” corresponds to batches 2-4 with Poka-Yoke implemented.
Although the objective focused on reducing variability and rejects, the pilot results show that by eliminating the special cause “worn thread” (present in batch 1), the number of non-conforming parts decreased from 10 to 5 per batch, representing a reduction from 20% to 10% in the rejection rate. This confirms that the implementation of SPC directly contributed to the process improvement.
Table: Percentage of Nonconformities per Batch (SPC Pilot by Attributes)
Pilot: 200 1/2” NPT threads in 4 lots of 50 pieces (n = 50). Note: %
Nonconforming = (d / n) x 100.
Table 2. Percentage of nonconformities per batch (SPC pilot by attributes).
Illustrations are not included in the reading sample
Data source: Pilot study documented with d = [10, 5, 5, 5] and n = 50 per batch (Author’s own work, 2026).
Figure 9. GOOD THREAD AND WORN THREAD
Illustrations are not included in the reading sample
Source: Author’s own work (2026) Figure 10.
GOOD THREAD AND BURNT THREAD
Illustrations are not included in the reading sample
Source: Author’s own work (2026) Figure 11.
WEARED PIPE
Illustrations are not included in the reading sample
Source: Prepared by the author (2026)
Figure 12. BATCH 1
Illustrations are not included in the reading sample
Source: Prepared by the author (2026) Figure
13. BATCH 2
Illustrations are not included in the reading sample
Source: Prepared by the author (2026)
Figure 14. LOT 3
Illustrations are not included in the reading sample
Source: Prepared by the author (2026) Figure
15. LOTS
Illustrations are not included in the reading sample
Source: Prepared by the author (2026)
Figure 16. Project Planning
Por motivos de protección de datos, esta fotografía no forma parte de esta publicación.
Source: Prepared by the author (2026) Figure
17. RIDGID 1224 Machine
Illustrations are not included in the reading sample
Source: Prepared by the author (2026)
Figure 18. General laborer Eduardo Espinoza
Por motivos de protección de datos, esta fotografía no forma parte de esta publicación.
Source: Prepared by the author (2026)
CHAPTER VI. CONCLUSIONS
This section synthesizes and analyzes the study’s findings in direct relation to the elements of Chapter I (problem statement, research questions, objectives, and hypothesis). The purpose is to provide a well-reasoned argument regarding the degree to which the general objective, specific objectives, and hypothesis were met, using as evidence the records from the SPC pilot by attributes, the diagnostic survey, and the “before vs. after” comparison documented in the results chapter.
6.1 Research Findings: Was the general objective of the research achieved?
The general objective was formulated as the implementation of a Statistical Process Control (SPC) system in the threading operation with the RIDGID 1224, aimed at reducing process variability and lowering the percentage of rejected threads. This objective was approached from an applied perspective, that is, under real operating conditions, with the intention of establishing a replicable method that is not dependent on a single person.
To operationalize the SPC, a key methodological decision was made: due to the absence of NPT GO/NO-GO gauges, control was initiated by attributes (Conform/Non- conform), supported by standardized visual inspection criteria and a functional coupling test with a standard connection. This decision allowed the process to be measured and controlled with available resources without losing focus on stability and variation reduction.
Implementation was demonstrated through a structured pilot study involving 200 1/2” NPT threads distributed across four batches of 50 pieces (constant n). The fixed sample size made it appropriate to use an np chart to monitor the number of nonconformities per batch. The results obtained were d = [10, 5, 5, 5] nonconformities in batches 1 through 4, respectively. This evidence confirms that there was systematic recording, a sampling logic, and a statistical monitoring tool associated with SPC.
Analysis of batch 1 revealed a significant deviation attributable to a special cause: the defect known as “worn thread.” The cause was linked to a process adjustment parameter (insufficient distance between the head and the press), affecting the consistency of the threading. In response, a simple Poka-Yoke was established: standardizing a minimum distance of > 7.5 cm. Subsequently, the “worn thread” defect ceased to occur in lots 2-4, representing a direct reduction in variation due to the elimination of the special cause.
The improvement was demonstrated quantitatively by expressing performance as the percentage of nonconformities per batch. In batch 1, before standardizing the distance, 10 nonconformities out of 50 were recorded, equivalent to 20%. In lots 2-4, after applying Poka-Yoke, 5 nonconformities out of 50 were recorded, equivalent to 10% per lot. Therefore, within the pilot framework, a reduction in the rejection rate from 20% to 10% was observed starting with batch 2. For the purposes of the before/after design, “before” corresponds to batch 1 (without intervention) and “after” corresponds to batches 2-4 (with intervention implemented).
Additionally, a thermal pattern was documented toward the end of the batches (appearance of “burnt” threads and cracks). This finding identifies additional sources of variation that require operational controls (standardized lubrication, breaks, periodic comb inspection, and preventive maintenance). Far from invalidating the achievement of the overall objective, this point strengthens the analysis because it shows that the process already has a mechanism to visualize variation, isolate special causes, and guide subsequent control actions.
Conclusion 1.1: Based on the evidence from the pilot and the before/after comparison, it is concluded that the overall objective was met within the evaluated scope, as an attribute-based SPC scheme was implemented, variability was reduced by eliminating a special cause, and the percentage of nonconformities decreased from 20% to 10% in the “after” phase. In addition, standardization parameters and mechanisms (checklist, response plan, and critical adjustments) were established to sustain the improvement and scale it to other process sizes or conditions.
6.2 Research Findings: Were the specific research objectives met?
6.2.1 Specific Objective 1: Measure and record critical variables of the threading process ( ).
The fulfillment of this objective was reflected in the definition of critical-to-quality (CTQ) variables and in the formalization of the process record. Functional conformance (pass/fail) via a mating test was defined as CTQ-1, and visual condition (e.g., “burn” as an early warning sign) was defined as CTQ-2. Additionally, batches with a constant n were recorded, nonconformities (d) were counted, and dominant defects were documented, which provided traceable data for statistical analysis.
6.2.2 Specific Objective 2: Develop SPC charts (X-R, histograms, Pareto charts) to evaluate process stability.
This objective was addressed with a justified technical adaptation. Since dimensional control by variables requires measurement with GO/NO-GO gauges (not available in the workshop), attribute-based SPC was used, and an np chart was applied, which is appropriate when the sample size is constant. The np chart allowed for evaluating stability, distinguishing common variation from special causes, and supporting decisionmaking. In this regard, the objective’s purpose (to evaluate stability using SPC) was fulfilled with the statistical tool appropriate for the context. X-R charts eonsidered a subsequent phase contingent upon having dimensional measurements; histograms and Pareto charts can be integrated in greater detail by expanding the defect log by type.
6.2.3 Specific Objective 3: Identify root causes using the Ishikawa diagram and the 5 Whys.
The causal analysis was conducted by combining a diagnosis of the work method with findings from the pilot study. The diagnosis (based on a survey and observation) identified human and method-related factors: variation in the sequence of steps, lack of standardization in lubrication, need for formal training, time lost due to head readjustment, and errors caused by distraction (cell phone use). These findings align with the Ishikawa approach by grouping causes related to labor, method, machine, and environment. Subsequently, the pilot study allowed for a deeper exploration of a verifiable root cause: the “worn thread” was linked to a physical parameter (head-to-press distance). The elimination of the defect following the correction confirms the cause-and-effect relationship and strengthens the validity of the analysis.
6.2.4 Specific Objective 4: Propose corrective actions related to lubrication, wear, and operating parameters.
This objective was achieved by proposing and standardizing specific corrective actions. Minimum operating parameters were defined: distance > 7.5 cm, lubrication by volume (0.5 L per 100 threads), breaks of > 1 hour between batches, systematic inspection of combs, and a response plan to contain variation when nonconformities increase. These actions address the issues described in the problem statement: friction/temperature, comb wear, and lack of control over critical parameters.
6.2.5 Objective 5 5: Validate the improvement through a before/after comparison of the process.
Validation was performed using the before/after scheme defined for the pilot. The “before” was established as batch 1 prior to standardization of the critical parameter; the “after” as batches 2-4 with standardization applied. The comparison showed two consistent results: (1) elimination of the “worn thread” defect in subsequent batches and (2) reduction of the nonconformance rate from 20% to 10%. This evidence confirms that the improvement was validated within the proposed pre-experimental design.
Conclusion 1.2: The specific objectives are considered fulfilled within the framework of the attribute-based approach and current metrological limitations. Critical variables were measured and recorded, SPC was applied using an np chart, relevant causes were identified, and corrective actions were proposed and validated with a quantified before/after comparison. The use of X-R is technically justified as a subsequent step when dimensional measurement instruments are incorporated; however, the control system remained operational and demonstrable with the indicators used.
6.3 Hypothesis: Which one was fulfilled? Justification regardless of the answer
In Chapter I, two hypotheses were proposed: Ho (the implementation of SPC does not reduce variability or the rejection rate) and H1 (the implementation of SPC does reduce variability and decreases the rejection rate). According to the results of the pilot study and the before/after comparison, the hypothesis that is fulfilled is the alternative hypothesis (H1).
Justification: The pilot study showed that formal process control allowed for the detection of a significant deviation in batch 1 associated with a special cause. Correcting the critical parameter (minimum distance > 7.5 cm) eliminated the recurrence of the “worn thread” defect in lots 2-4 and reduced the nonconformance rate from 20% to 10%. This result simultaneously demonstrates two central components of the hypothesis: a decrease in variability (elimination of the special cause) and a decrease in the rejection rate (percentage reduction).
In contrast, the null hypothesis (Ho) is rejected for the scope of the pilot, since a measurable improvement was observed following the intervention. However, the finding of the thermal pattern (“burnt” threads and cracks at the end of the batches) indicates that there are still sources of variation to be controlled, primarily associated with friction/temperature and wear. This point does not invalidate the fulfillment of H1; rather, it defines the next improvement cycle: maintaining the reduced rejection rate and addressing thermal variation through standardized lubrication, breaks, and comb management.
Conclusion 1.3: The alternative hypothesis (H1) is met, since the implementation of attribute-based SPC is associated with a quantified reduction in the percentage of nonconformities and with the elimination of a special cause that was generating variability in the process.
6.4 International support for the results of the diagnosis and pilot
Theoretical support document (authors, citations, and references)
6.4.1 Purpose of the document
This document presents a review of international literature and sources that support the findings obtained in the applied research conducted at GONDEL S.A. on
C.V. on variability, rework, and rejections in NPT threads produced on the RIDGID 1224. The results of the diagnostic study (survey) and the SPC pilot are linked to internationally recognized authors and organizations.
6.4.2 Key findings of the study (summary)
• There is no single standard for lubrication; variation in lubrication practices was observed among operators (González Herrera, 2026).
• Some staff report no or only partial formal training; informal learning and “personal methods” are inferred (González Herrera, 2026).
• The main time losses are related to head readjustments and unprepared comb changes (González Herrera, 2026).
• Defects associated with friction/temperature are concentrated in “burnt” threads and cracks (González Herrera, 2026).
• The “pass/fail” acceptance criterion is not uniform (visual vs. fit), which increases repeated inspections and uncertainty (González Herrera, 2026).
• Recurring human errors (cell phone use, improper postures/movements) are identified, and behavioral Poka-Yoke is proposed (González Herrera, 2026).
6.4.3 International evidence supporting each finding
Process variability and the need for SPC (common causes vs. assignable causes) The study proposes implementing SPC to distinguish natural (common) variation from variation due to special (attributable) causes, stabilize the process, and reduce attribute nonconformities.
• Shewhart establishes the basis of statistical control through control limits to distinguish when a process “varies more than is economically desirable” and to identify out-of-control conditions (Shewhart, 1931).
• Montgomery describes control charts (including those for attributes such as p and np) as central SPC tools for monitoring the proportion of nonconformities and taking corrective action when the process goes out of control (Montgomery, 2020).
Implication for GONDEL: the use of an np chart with a constant n (per batch) is consistent with the classical SPC literature for nonconformities when inspection is by attributes.
Lubrication, friction/temperature, and defects (burnt thread, burrs, wear)
The diagnosis reports variation in lubrication and associates friction/temperature with defects such as “burnt thread” and cracks. The machining literature explains that lubrication (cutting fluid) reduces friction/temperature, improves surface finish, and extends tool life.
• Pang et al. report that cutting fluids with better lubricant film formation reduce cutting force and roughness and increase tool life; they highlight the role of the lubricant in surface quality and wear (Pang et al., 2023).
• Mir and Wani show that fluid conditions (particularly flow rate/velocity configurations) can reduce tool wear and improve surface finish; they also describe that the fluid must penetrate the interface to form a film with low cutting resistance and reduce friction and heat (Mir & Wani, 2018).
Implications for GONDEL: Standardizing lubrication (frequency/quantity) and ensuring its consistent application is consistent with international evidence regarding the reduction of temperature, wear, and surface defects.
Tool wear (combs) and quality variation
The study identifies the need to inspect the cutting edge and condition of cutters and links wear to fit defects (loose/tight), burrs, and cracks. In machining, wear affects cutting edge geometry, forces, temperature, and surface integrity.
• Demirpolat et al. describe that tool wear has a decisive influence on cutting edge geometry and surface/dimensional quality; furthermore, high temperatures in the cutting zone affect finish and tool life, and lubrication helps control them (Demirpolat et al., 2023).
• Mir & Wani report wear mechanisms (adhesion, abrasion, chipping) and show that fluid condition influences wear and roughness; they support the need to control tools and parameters for stability (Mir & Wani, 2018).
Implications for GONDEL: a comb logbook and criteria for replacement/inspection by piece or by batch align with the tool condition control approach for process stability.
Training, standardized work (SOP), and reduction of operator variation
The diagnosis indicates partial or no formal training and differences in method (order of steps, adjustments). Lean and quality management literature establishes that standardized work/SOPs and training reduce operator variation, improve cycle time, and enhance quality.
• Imai describes Kaizen as continuous improvement based on standards (standardize, measure, and improve) and emphasizes standardization as the foundation for sustaining improvements and preventing process regression (Imai, 1986).
• Islam and Ahmed demonstrate, in a Lean improvement case study, that work standardization (flow, standard time, and standard quantity) can increase productivity and reduce lead times/waiting times; they also integrate tools such as 5S and SPC into the approach (Islam & Ahmed, 2024).
Implications for GONDEL: documenting the correct sequence (SOP) and training everyone reduces “personal methods” and makes head adjustment and inspection more repeatable.
Poka-Yoke (error prevention) and control at the source
The study proposes a pre-threading checklist and Poka-Yoke (e.g., minimum spindlepress distance) to eliminate repetitive errors. Shingo’s literature establishes error prevention at the source as the path to zero defects.
• Shingo argues that the combination of source inspection and Poka-Yoke devices is the practical way to reduce errors and approach zero defects, with examples of simple, low-cost solutions (Shingo, 1986).
Implications for GONDEL: the minimum distance Poka-Yoke and the pre-checklist are consistent with “control at the source” to prevent defects from occurring, rather than detecting them too late.
Order and Cleanliness (5S) as Support for Quality and Timelines
The survey indicates that order/cleanliness affects lead times and quality. The 5S literature supports the claim that “housekeeping” reduces waste, improves productivity and quality, and helps sustain standardization.
• Chandrayan, Solanki, and Sharma review evidence that 5S (Seiri, Seiton, Seiso, Seiketsu, Shitsuke) improves efficiency, productivity, and quality by making the workplace orderly and standardized (Chandrayan et al., 2019).
• Islam & Ahmed integrate 5S with standardization, SPC, and PDCA, demonstrating performance improvements and reductions in lead times in a manufacturing environment (Islam & Ahmed, 2024).
Implications for GONDEL: 5S ensures that combs and tools are “ready,” reducing time lost to searching or preparation, and supporting consistency in the method.
Phone Distractions and Task Fragmentation (Human Factor)
Open-ended responses identify cell phone use as a common mistake and source of distraction. The international literature documents that smartphones can act as distractions in work contexts and can lead to interruptions and task fragmentation.
• Heitmayer experimentally analyzes how smartphone accessibility affects device use and task fragmentation; even when phone use is reduced by moving the device away, distraction can shift to other media, which supports the need for rules, notification control, and workplace design to reduce interruptions (Heitmayer, 2025).
Implications for GONDEL: a behavioral Poka-Yoke (visual “no cell phone” rules, safe zone, defined breaks) is consistent with the approach to managing interruptions and habits.
Documentation, traceability, and evidence (ISO 9001:2015)
The project proposes SOPs, checklists, logs, and SPC records. The ISO guide on “documented information” explains that documentation serves to communicate, demonstrate compliance, and preserve knowledge, and that its scope depends on the process and the competence of the personnel.
• ISO notes that documented information is used to communicate, provide evidence of what has been done, and share knowledge; furthermore, ISO 9001:2015 requires maintaining documented information necessary to support the operation and control of processes (ISO, 2015).
Implication for GONDEL: maintaining records (SPC, comb/adjustment log) and operational documents (SOP/checklist) is aligned with a documented and auditable quality management system.
6.4.4 Summary Matrix: Findings and International Support
Table 3. Matrix of findings and international support
Illustrations are not included in the reading sample
Note: The findings of the diagnostic/pilot study are taken from the GONDEL research document (Author’s own work, 2026).
6.5 International critiques (negative comments) relevant to the research results
International sources (authors/organizations) are presented that point out LIMITATIONS or RISKS of approaches similar to those used in the project (SPC by attributes, visual inspection, Kaizen/Lean, Poka-Yoke, 5S/standardization, lubrication/cutting fluids), to critically contrast the results and strengthen the discussion.
Table 4. Matrix of negative comments with international support
Illustrations are not included in the reading sample
CHAPTER VII. RECOMMENDATIONS
Based on the results obtained during the project, it is considered essential that improvement actions not be limited solely to the pilot study conducted, but rather become a systematic and ongoing practice within the workshop.
7.1 Consolidate the Statistical Process Control (SPC) system using attribute- .
Establish a formal mechanism for monitoring the threading process, continuing to use the NP chart to track the number of nonconformities per batch and utilizing the data obtained as a basis for operational decision-making. This recommendation is particularly relevant in the workshop’s current context, where NPT GO/NO-GO gauges are not yet available; therefore, until these instruments are incorporated, the attribute-based approach must be strengthened as the primary means of controlling variability and responding promptly to process deviations. At a later stage, once more precise measuring instruments are available, it will be advisable to transition to variable SPC using X-R charts to achieve more accurate control over the depth and effective diameter of the thread.
7.2 Rigorous standardization of lubrication.
Since the results of the diagnostic analysis and pilot test show that friction and temperature are critical factors in the development of defects, particularly in what is known as “burnt thread,” it is proposed to maintain an operational standard of 0.5 liters of lubricant per 100 threads, with compliance recorded on a mandatory checklist before and during the operation. This measure not only helps stabilize the process but also extends the service life of the dies, reduces the risk of cracks, and minimizes thermal variation between batches. Lubrication, therefore, must cease to depend on the operator’s individual judgment and become a standardized, verifiable, and auditable parameter.
7.3 Standardize staff training and establish a Standard Operating Procedure (SOP) .
Research shows that part of the process variability is associated with differences in operating methods, the order of steps, die head adjustment, and comb inspection. Therefore, it is necessary for all operators to receive documented and standardized training, focused not only on the correct use of the machine but also on the interpretation of defects, acceptance/rejection criteria, the importance of statistical control, and the application of Kaizen practices. The SOP must clearly outline the operating sequence, critical process parameters, inspection points, and corrective actions for deviations. Additionally, it is recommended to periodically audit compliance with this procedure to prevent the process from reverting to reliance on individual habits or informal knowledge passed down among operators.
7.4 Maintain the pre-threading checklist and the Poka-Yoke for minimum distance between the head and the press.
The study demonstrated that a minimum distance of > 7.5 cm eliminates the recurrence of the defect known as “worn thread,” so this condition must be established as a mandatory requirement before starting any batch. The checklist must include, at a minimum, verification of lubrication, critical distance, condition of the dies, deburring, part alignment, and availability of master gauges. The advantage of this approach is that it transforms a one-time corrective action into a permanent preventive practice, reducing the likelihood of defect recurrence and improving the overall reliability of the process.
7.5 Formal log of dies and head adjustments.
The wear of these tools and configuration changes directly influence threading quality. It is recommended to record the installation date, estimated number of parts produced, visual observations of the cutting edge, and adjustments made, in order to correlate process performance with the actual condition of the tool. This information would allow for the establishment, in the medium term, of technical criteria for replacing dies based on the number of parts produced, visual condition, or the recurring occurrence of specific defects. In this way, maintenance would shift from being reactive to a more preventive and controlled approach.
7.6 Formal response plan for increases in non-conformities.
When the process shows signs of an increase in defects, the recommended procedure should be: halt the batch, review the critical parameters (distance, lubrication, comb condition, and cleanliness), validate the adjustment using at least three consecutive conforming parts, and document the corrective action taken. This response plan strengthens operational discipline and prevents the workshop from continuing to produce non-conforming parts when the process already shows clear signs of instability.
7.7 Systematic monitoring of cycle times by batch and by operator.
Identify waste and consolidate improvements under the Kaizen approach. The results show that activities such as head readjustment, lack of prior comb preparation, and certain repetitive inspection practices generate wasted time and increase operational variability. Therefore, measuring cycle times and analyzing them regularly will allow for the detection of opportunities for improvement in method, sequence, and work preparation, thereby reducing significant differences between operators.
7.8 Clear behavioral rules and layout improvements.
Notable among these are the prohibition of cell phone use during operations, the placement of materials at an ergonomically convenient distance, and training in safe postures and efficient movements. These recommendations have a dual effect: on the one hand, they reduce errors resulting from distraction; on the other, they promote a more fluid, safe, and consistent operation.
Additionally, it is recommended to implement the 5S methodology in the work area, with periodic audits of order and cleanliness, tool availability, and proper material arrangement, so that the work environment does not contribute to process variability.
7.9 documentation, traceability, and the sustainability of improvements.
All SPC formats, checklists, logs, SOPs, and records of corrective actions must be kept up to date and accessible, not only as evidence of process control but also as a basis for internal audits and continuous improvement. In turn, it is advisable to assign a person directly responsible for the monthly monitoring of indicators, the review of operational compliance, and the updating of procedures as new findings accumulate. In parallel, given that the process involves lubricants and metal waste, it is also recommended to manage their disposal responsibly and, where feasible, evaluate more environmentally friendly alternatives, aligning process improvement with sustainability criteria. In this way, the recommendations will not only strengthen the quality of the threading but also contribute to the sustainability of the improvement over time and the professionalization of the workshop.
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