Faking a 1/2" whitworth thread

[bob ward]

I try to do all my machining in metric, but I couldn't avoid having to cut a one off 1/2" 12 TPI whitworth thread. And I didn't have the proper 55° insert.

55° threading inserts are 10 for $100, and not sold singley at the local supplier, so they were out of the question, and I haven't turned my mind to grinding HSS yet.

Then I had a brainwave. I cut to 90% of the required thread depth with a 60° insert, and finished the thread with a 1/2" whitworth die nut. Worked like a charm.

 

[Lew Hartswick]

Theres always, grinding a high speed steel bit.
...lew...

 

[kvom]

As my shop instructor said last week, the main advantage of a single point thread vs. a die-cut thread is that the single-point is concentric, whereas a die might not be started straight. He went on to say that partially cutting a thread with the lathe to ensure concentricity, and then finishing with a die would be entirely satisfactory.

You probably didn't need to cut anywhere close to 90% to get the result you wanted.

 

[Hexbasher]

i was cutting BSP and BSPT threads all this week at work in manifolds....

 

[Bogstandard]

Bob,

Instead of having to use a 55deg tool, you could have cut the thread as a 60 deg. UNC standard, they are very close to whitworth and are used in the same context.
Course threads for soft metals and materials.
They are not compatible over a long run (IE they won't fit each other) but it is a thread that can be used instead of, and also vice versa.

John