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Cutting The Modified Square Thread-Brake rod (Part 4).

  Cutting The Modified Square Thread-Brake (Part 4). 


Me aged: 53
Software Engineer
Machinist, with zero tolerance to mistakes..

Simple Idea: Making a Tap from a Threaded Rod

Hello everyone—just sharing a simple idea I’ve been trying.

Instead of scrapping a brake rod, I decided to practice screw cutting and then use the best threaded piece to make a tap. The goal is to create a matching internal thread for a nut. The brake rod has been completed (As above) but this has taken a few practice goes before committing to this. The results of which I am very pleased with and the square threads look the part as compared to just cutting a metric thread of say 8mm. 

What I did

  • Cut an external thread on the rod
  • Used a 4 mm ball-end cutter to make three flutes
  • Offset the cutter slightly to give a bit of rake
  • Cleaned up the edges with a file
  • Case hardened the tool

The idea behind it

If the external thread is correct, turning it into a tap should produce a matching internal thread.

What to expect

It should work for light use, it will be used for just one go at the brake nut in bronze. The rounded flutes and basic relief mean it’s not as effective as a proper tap, but good enough for this job.

I planned to use a new 4 mm ball-end cutter as purchase, to machine three straight flutes, offset slightly from the centreline to create a positive rake—about 0.008" (around 3% of the tap diameter).

After cutting the flutes, I would clean up the edges with a Swiss file to sharpen them and add a bit of relief. Then I’d case harden the finished tap.

The offset will create a positive rake, though it’s slightly conservative because I forgot to add on half the width of the tool initially. (A slight boo boo).

Finally from Co-pilot: 

Bottom line

Drill 19/64" (0.2969") /  7.5mm    to cut a 3/8‑12, 10° alternative thread in bronze.



Did it work?

It cut the start of a thread, it was hard going and I almost gave up but once I was 2/3 of the way up the tap things started to improve. The tap was by no means sharp but the result was a reasonable suggestion of the thread in the bronze. However the proper shaft did not fit after, my idea of making 3 taps in one was hopeful. I believe the next step is to make a kind of plug tap, to further enhance the thread it have already started.  More opportunity to practice screw cutting and a change from routine machining.     


Feel free to leave a comment !!     stephen.meredith1@gmail.com

If you have any questions while reading these blog updates—I'm always happy to reply.



Until Next month, stay safe, make swarf and be the best you can be.
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