---
title: "Production of screw threads"
subject: "Workshop Technology"
chapter: 11
key: "semester_2/workshop_technology:thread-production-methods"
source: https://www.bctengineer.com/q/semester_2/workshop_technology/thread-production-methods
site: BCT Engineering
---

# Production of screw threads

Workshop Technology · Chapter 11: Screw Threads and Gear Manufacturing Methods

- Asked in: year not given, 5 marks
- Video: [Screw threads methods of producing threads](https://www.youtube.com/watch?v=bLnsP5tPAcA) — Saroj Mohanty
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/workshop_technology/thread-production-methods
- Whole chapter: https://www.bctengineer.com/md/semester_2/workshop_technology/chapter-11

## Question

Describe the methods of producing screw threads by (a) machining, (b) rolling and (c) grinding. Why are rolled threads stronger?

## Short answer

Threads are machined by single-point cutting on a lathe, taps and dies, or milling; rolled by pressing between hardened dies causing plastic flow; ground with a formed wheel for accuracy on hardened parts. Rolled threads are stronger because grain fibres follow the contour, cold working raises strength 10–20%, and surface compressive stress improves fatigue life.

## Answer

#### (a) Machining methods
- Single-point cutting on a lathe: a tool ground to the thread form is moved by the lead screw; flexible but slow, used for single parts.
- Taps and dies: hand or machine cutting of internal and external threads.
- Thread milling: a single-form cutter traverses along the thread, or a multiple-form cutter on a thread milling or CNC machine cuts the full thread length in about one revolution of the work.
- Self-opening die heads, thread chasing and thread whirling for production work.

#### (b) Thread rolling
The blank is pressed between hardened dies carrying the thread form, and the metal is made to flow plastically (cold working) to form the roots and crests, with no chips.
- Dies: flat dies (one stationary, one reciprocating), or two or three cylindrical rolls fed radially.
- Very fast (hundreds of parts per minute); used for bolts, screws and studs.

#### (c) Thread grinding
A grinding wheel dressed to the thread form (single-rib or multi-rib) is traversed along the rotating job. It gives high accuracy and a fine finish and can produce threads on hardened parts: lead screws, taps, gauges, ball screws. Centreless thread grinding is also used.

#### Why rolled threads are stronger
- The grain fibres follow the thread contour instead of being cut across.
- Cold working increases the hardness and surface strength (tensile strength rises by about 10 to 20%), and the smooth surface with residual compressive stress greatly improves fatigue life.
- There is no material waste.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which describes single-point thread cutting on a lathe?
   A. A tool ground to thread form is moved by the lead screw; flexible but slow
   B. Dies press the thread without chips
   C. A threaded wheel grinds the thread
   D. A hob generates the thread
   Answer: A. The lead screw feeds the form tool, which suits single parts but is slow. (Key point: Single-point thread cutting)

2. How does thread rolling form a thread?
   A. Chips are removed by a tap
   B. Hardened dies press the blank so metal flows plastically, with no chips
   C. A grinding wheel cuts the form
   D. The blank is heated and cast
   Answer: B. Cold working by dies makes the metal flow into roots and crests without chips. (Key point: Thread rolling process)

3. What is thread grinding especially suited for?
   A. Mass production of ordinary bolts
   B. Soft aluminium screws
   C. Accurate, fine-finish threads including hardened ones such as lead screws and gauges
   D. Internal threads in castings
   Answer: C. Grinding gives high accuracy and can cut hardened threads. (Key point: Thread grinding)

4. Why are rolled threads stronger than cut threads?
   A. They have more material removed
   B. Grain fibres follow the thread contour and cold working hardens the surface, improving fatigue life
   C. They are heat treated afterwards
   D. They have sharper root corners
   Answer: B. Uncut grain flow plus work hardening and compressive stress improve strength and fatigue life. (Key point: Why rolled threads are stronger)

## Related in other subjects

- [Screw thread production and change gears](https://www.bctengineer.com/question.md?key=semester_4%2Fmanufacturing_and_production_processes%3Ascrew-thread-manufacturing-change-gears) — Manufacturing and Production Processes, chapter 11
- [Power screw threads, standards and materials](https://www.bctengineer.com/question.md?key=semester_7%2Fmachine_design_ii%3Ascrew-thread-types-standards-stress) — Machine Design II, chapter 8
- [Grinding wheel specification and selection](https://www.bctengineer.com/question.md?key=semester_4%2Fmanufacturing_and_production_processes%3Agrinding-wheel-designation-selection) — Manufacturing and Production Processes, chapter 8
- [Screw jack with square thread](https://www.bctengineer.com/question.md?key=semester_7%2Fmachine_design_ii%3Ascrew-jack-square-thread-numerical) — Machine Design II, chapter 8