G76, Troubleshooting needed!

Stuttering could be a mechanical or PID resonance. Is this a servo or stepper machine?

(My first stepper lathe stuttered awfully, but LinuxCNC was rapidly improved to avoid that)

Do you want to make left-handed threads in M4 mode?

I can't say I have tried it. You might just have to experiment with air cuts. What does a negative pitch give you?

Hi Andy.

Agreed it could be resonance but i'm pretty sure it's not the case this time, i've never heard anything like it in my lathe until i started running the G76.

To exclude the chance of resonance i tested a code like this:

G0 X20 Z80 M4 S1200
G33 Z40 K1
G0 Z80
G95
G1 Z40 F1

this makes the lathe to first run the spindle synchronized motion with 1200rpm and a feed of 1 rev/turn
after it does the exact same move again without the spindle synchronized motion but still with 1200rpm and feed of 1 rev/turn

And the difference is clear with G33/ G76 it's stutters very bad and without it it's super smooth.
If i drop the rpm to 400 the feed is smooth with G33 and if i increase the rpm to 1400 it's also smooth but at certain rpm's it's bad!
How do i solve this? is there any filter for the encoder input that could be applied? or are there other ways?

You can check this link to my onedrive with a movie clip of it:
G33 Test video

And regarding M4/M3 threading, will i do left hand threads everyday, no absolutely not but i'm sure i will make them from time to time.
So both M3 and M4 threading would be nice have.
How would i solve that?

Br Victor

What type of encoder do you have?

Have you tried plotting the encoder position?

Hi,

I don't really know what brand of encoder it is, i'm still using the one that was mounted originally on the Emco lathe at the factory.

It's not a quadruple but i have one 150ppr signal and one 1ppr signal.

there are some info here:
emcocncretrofits.wikia.com/wiki/Spindle_encoder
The encoder on the link does however have 360ppr but i suppose there might have been variations from year to year during manufacturing.

Could you elaborate what plotting the encoder position is?

Br Victor

I mean using halscope to see if the encoder position or velocity are noisy

Ok! I will check tomorrow and make a screenshot!

Br Victor