Arch, I forgot that the newest SmoothStepper plug-in included the ability to use a standard encoder for the spindle. So using the A or B channel should work fine. Encoder signals can get swamped with noise from the spindle motor. I had this happen when I added a VFD and three phase motor to a piece of test equipment that was previously working fine. The noise from the motor/VFD was enough to confuse the National Instruments controller. The solution was to fit a differential encoder which was powered by an isolated power supply.

If you have access to an oscilloscope you can check the quality of the signal getting to the SmoothStepper. This will let you know if noise is an issue.

The other things to look for are how stable your spindle speed is and how much you are trying to cut in a single pass. You can start up the spindle and watch the RPM display in Mach while you apply some load. Is it easy to slow the spindle down? Then take a really light threading pass, just enough to scratch the surface. Does the pitch stay consistent?

Jeff,
Thanks for the information.
Strangely I get pretty stable RPM on DRO at 348 RPM +/- 1 . Also there is almost no change in RPM while cutting. Cutting depth is about just 0.1 MM  per pass so that should not be a problem. As I have pointed, I have set my Encoder input with " Spindle Index Prescale" =1000 as shown in SS Plugin setup. But when I undertake multipass threads, the pitch drifts and at the end of several passes say 20, it is hard to find clear threads..
I have a VFD connected to spindle running at full RPM. I will try to see if noice is my issue. But in that case, I should not be getting a stable RPM on DRO. Suggestions are requested.
M Vyas.

A few stray pulses from a VFD will not effect the RPM reading much but could effect the threading timing. You can try adding some noise filtering to the index pulse in the SS config screen. You might also want to post this on the Warp9 forum so Greg from Warp9 will be sure to see it.

Jeff do you know if the newest plugin resolves the Step/dir spindle issues that have been present since the start?
I looked at the site but no changelog on the plugin page so no idea what has been done in them.
Hood

I'm not sure about that Hood. I'll be talking to Greg today so I'll ask him

Ok thanks. Last time Greg skyped me he said he was going on holiday and would try and get it sorted but never heard back from him again so just presumed he didnt/couldnt. Maybe he did manage after all.
Hood