Thread tool angles

[Bryan]

Hands up who grinds rake on threading tools? My text book says not to because the angle will be wrong. Having turned a few rough threads, I wanted to find out just what effect rake would have, and if it could be compensated for. Not being maths-savvy enough to calculate it, I drew it instead. I made a 3D model of a 60 deg 1/2 x 13 tpi UNC thread, drew a plane inclined at 16 degrees, and measured the angle of the point. It comes to 59.9 deg. To heck with a tenth of a degree I say!

You may notice my thread model is made of segments rather than true curves, and this might change the result. But it's the best I could do. If someone else can model it better, or calculate it, go your hardest. For the record I did try to also model a fine thread to see if it made any difference, but I'm having some trouble with Google Sketchup. It can be a bit, er... sketchy. Anyway I intend to try grinding up a 60 deg tool, inclined at whatever, and see what happens. Maybe try a direct comparison.

[pipeclay]

I grind rake on my tools depending on application and material.

[nadroj]

Nice effort Bryan.
I don't find however that the lack of back rake is a problem, possibly because threading is done at such a slow speed?

Jordan

[old_fella]

I never grind it on a threading tool as it is a form tool and you usually dont grind a rake on a form tool and that is what i was taught at tafe doing my fitting ang machining apprenticeship. But alot of people do and would probably help if u were to be cutting threads with a large pitch, and i dont think a 10th of a degree would matter just cut it a bit deeper