Threading problem

Rick and Chris - I am fairly certain the belt isn't slipping, it's pretty tight and there is almost no resistance on the encoder.

CNCBasher - I think you are on to something with the scale.

I did a test, turning the spindle by hand over 10 revolutions I get the scale at 4134 PPR rather than the 4096 - this obviously is the small mismatch between my encoder pulley and the spindle pulley.

Any ideas how to alter the hal file. I tried just changing the encoder scale to 4134 but that didn't seem to make a difference as I think the index pulse would need to be scaled too?

Basically the math seems that 1 revolution of the spindle = (4134/4096) = 1.00928 revolutions of the encoder.

Chances are the pulleys on the encoder and spindle are not identical.

Exactly - I can adjust the scale to account for it but how do i adjust for the index being off a bit in Hal?

Adjusting the scale will NOT work. You MUST have a positive 1:1 ratio spindle to encoder.
At least the index pulse must be 1:1.
Please save youself a lot of trouble and get a timing belt or gears.

Joe - Thanks for that - it really confirmed what I was thinking.

So I kept the quadrature encoder as it is and adjusted the scale to 4114 (up from 4096) based on 20 hand revolutions of the spindle and dividing the spindle count by 20.

I added this for the index pulse:



and as you can see the results are much better:



Here's the video as well.



Thanks for everyones help!

Looks great.
May I suggest starting your thread at Z.100" or even Z.200" to be sure everything is up to speed at the actual thread.