Question re G76 threading code

andypugh wrote: I don't actually understand what you don't understand.

Q is a virtual compound slide angle. The thread forming tool necessarily has to be perpendicular to the work, or it won't form a thread.

Thank you for being so patient Andy You have just lit the light bulb for me. with the "Q is a virtual compound slide angle" I could not get my head around whether to physically set the compound on the slide to 29.5 or linuxcnc does it with the Q setting thus keep the physical compound at 0.

Thanks again.

I was getting confused because I have not seen a CNC lathe with a compound slide.

(I have converted two manual lathes and removed the compound in both cases to increase stiffness)

andypugh wrote: I was getting confused because I have not seen a CNC lathe with a compound slide.

(I have converted two manual lathes and removed the compound in both cases to increase stiffness)

Ah I see my bad. I am in the process of removing the compound as you say it is not necessary.

I am sorry to open an old thread "but"

I would like some help with the G76  I,J and R commands

My small lathe cuts threads ok but on bigger threads and coarser pitches I would like to makes more passes.
This is the code I use for m10 thread
G0 X10 Z10
G76 P1.5 Z-12 I-0.1 J0.1 R1 K1.5 Q29.5 L0  H1

what controls the number of passes?

From the manual   linuxcnc.org/docs/2.8/html/gcode/g-code.html#gcode:g76

I- - The thread peak offset from the drive line. Negative I values are external threads, and positive I values are internal threads. Generally the material has been turned to this size before the G76 cycle.


 

R and J together control the number of passes, and then H spring-passes are added on top.

Fot coarser threads you can probably use the same J as you do already but set R to 2 so that the increments get progressively smaller.

andypugh wrote:

R and J together control the number of passes, and then H spring-passes are added on top.

Fot coarser threads you can probably use the same J as you do already but set J to 2 so that the increments get progressively smaller.

Thanks. But did you mean J to 2 or R to 2

I did read some ware (but can't find it again) that is was something like J/R that would make more passes !!

Edited. I did mean R.

Why not try threading some air and counting the passes?

andypugh wrote:

Edited. I did mean R.

Why not try threading some air and counting the passes? 
Yes of course I will.

Thanks for the input.


 

I = 0.1 R = 1 gives 10 passes

I = 0.1 R = 1.2 gives 16 passes

I = 0.1 R = 2 gives too many to count