How can I modify G76 to make it actually useful for internal threading?

Is it possible to modify G76 so it actually stays on the drive line when doing retract path?
I have been using G33 for internal threading ever since because with G76 with every cutting pass you end up retracting further away for the driveline, so when you have small clearance between tool holder and bore diameter you end up running tool holder into the work after few retract passes 
so now for whatever reason I want to use G76, can I modify source code to make that work properly?
 

radom wrote:

Is it possible to modify G76 so it actually stays on the drive line when doing retract path?
I have been using G33 for internal threading ever since because with G76 with every cutting pass you end up retracting further away for the driveline, so when you have small clearance between tool holder and bore diameter you end up running tool holder into the work after few retract passes 
so now for whatever reason I want to use G76, can I modify source code to make that work properly?

 

If you can post the code As I can check it on my lathe.

I don't see any problems with G76.

linuxcnc 2.8.2
TR40x10 thread,
30mm bore 
G7 G21
g0 x30 z0
g76 p10 z-60 i0.1 j0.4 k11
screenshot
goes 5.5mm into the cut per side and almost the same amount over driveline on the retract 
 

Re:-
g76 p10 z-60 i0.1 j0.4 k11

I think it should be G76 P10 Z-60 I-0.1 J0.4 K10

Figure 3. G76 Threading

• Drive Line - A line through the initial X position parallel to the Z.
• P- - The thread pitch in distance per revolution.
• Z- - The final position of threads. At the end of the cycle the tool will be at this Z position.

NoteWhen G7 Lathe Diameter Mode is in force the values for I, J and K are diameter measurements. When G8 Lathe Radius Mode is in force the values for I, J and K are radius measurements.

• 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.
• J- - A positive value specifying the initial cut depth. The first threading cut will be J beyond the thread peak position.
• K- - A positive value specifying the full thread depth. The final threading cut will be K beyond the thread peak position.

no, I'm cutting internal thread

I may not understand but I think the retract drive line is moved
parallel to the cut driveline to equalize the sync time available
before the tool starts cutting.

Ok I found solution for my problem,
11 years ago
www.mail-archive.com/emc-developers@list...ge.net/msg04863.html
now only if I knew how to recompile the source

radom wrote:

Ok I found solution for my problem,
11 years ago
www.mail-archive.com/emc-developers@list...ge.net/msg04863.html
now only if I knew how to recompile the source

Thank you I did not know it was doing that as I do not do much internal threading with tight bore.

Please post the answer here if you can.

took me awhile to compile run-in-place build but I finally got it
G76 P10 Z-60 I0.1 J0.4 Q14.5 K11
still don't understand what's the point of this safe_x+depth-end_depth
before and after