Can we have a tutorial on theadmilling using G41

Hi Can we please have a tutorial on Threadmilling using G41 instead or the software offset.
we are struggling to threadmill a M20 x 2.5 thread using a solid threadmill tool is 14mm dia, 3 fluted, with 14 threads.
The issues we have is that the cutter move out into the hole wall before it starts to raduis to thraed tooth depth, (if would be helpful to use side roughing and do spring cuts).

“The Threading and Tapping Handbook” by Horst Witte and Peter Brett. This book contains instructions for tapping and contains information on program control of tapping. “A Guide to CNC Programming” by Peter Smid. This book covers all aspects of CNC programming and includes the basics on tapping and using G-code to control tapping.

Hi AnnetWang,
Not sure what you are going on about, nothing you say is in anyway relavent to THREAD MILLING.
I have thread milled on load sof different CNC machines over the years, using either basic ISO programming, (G-Code), or using inbuilt thread milling cycles on the machine.
The issue that I am having with BobCad is that when the tool first move out, before it starts to arc into the start of the thread, it clashes with the side wall of the hole, thus sometimes leaving a dent in the thread.
see the pictures

It may be that you lead in or lead out radius is too big judging by the non-helical dents leftover. I’ve always found success with a small circular lead (somewhere around .025" R on a hole this size), bottom up and side roughing. On smaller holes I’ve even gone as little as .004" leads. Hope this helps.


thread test.bbcd (179.6 KB)

Hi Eric,
Thanks for the help with ThreadMilling
Just a quick question, why are you using tool to the right, (which would be G42), instead of using tool Left, (which would be G41).
Your Thread Mill program still works.

Your right but that is what they wanted at the mills.