Acme Threading Questions

yooper

Registered
Registered
Joined
Jul 8, 2013
Messages
35
I have a jet lathe and when I cut 60 degree threads I have to set my compound to 59 1/2 degrees. Now I want to cut acme threads the videos and such say to set the compound to 14 1/2 degrees ( this would be for USA machines) can someone tell me what the compound SHOULD be set to? Thanks Rick
 
They have a 29° included flank angle, so the 14°30' is half of that, same as the 30° is half the angle of a UN thread. Some people use 29°30', so to go the same route on the Acme, you would go 14° even.
 
To answer the unasked question, in general practice make it a rule to set the compound 1/2 the specified angle minus 1/2 º (approximately) off of square to the long axis of the part being threaded, regardless of the numbers on the saddle.
 
When I cut Acme threads I use a parting tool the width of the bottom flat or just slightly smaller and finish the sides with the compound set parallel to the ways of the lathe and a tool ground one size smaller than the desired thread pitch setting that tool to the root of the thread and advancing it forward and backward until I have cleaned up the sides and cut the thread to the desired dimension. This method will allow you to cut larger acme threads with much less tool pressure resulting in less chatter and better finishes.
 
Do you need the number 75.5? That's 90 - 14.5, like the 90-26.5 gave you 59.5.
 
I just use the cross slide for all my threading works great
In old books you will find setting the compound to 29 1/2 deg was use for direct reading so if you move the compound .001 the cut take off 0.001 off the diameter.
This was use for lathes have direct reading dials
This method is also use for tool post grinders for taking off 0.000,1 off the diameter.

Dave
 
Back
Top