I am configuring a lathe using a Mk3 board and PlanetCNC software. I believe that I have correctly connected and configured everything, but I cannot get the spindle to synchronise for screwcutting. Each pass starts in a different place.

I am using a 100PPR spindle encoder, belt-driven from the spindle via 1-1 pulleys. I have AB and index pulses connected to the CTRL port.

When I turn the spindle slowly by hand, the spindle speed is shown in the display (so I believe that the encoder AB pulses are correctly wired) and I see the Index LED on the IO panel flash once per rev.

The speed display appears to be correct - spindle speed shown is within a few percent of the set speed. On the "Spindle" settings page, I have set PPR=100, Index PPR=1, and debounce to 0. I have tried "Spindle RPM" and "Sync Signal" with all combinations of "From Index" and "From Encoder" without this making any difference.

I have tried to read through the "Settings" section of the manual (copy which came with the software distribution dated 2022/07/25) but I see that there are at least one or two parameters in the Settings dialogue that are not described in the manual. Specifically, under Settings->Program Options->Speed, there is an entry for "Sync Speed" and I have no idea what that does or if it is relevant here - but it sounds as if it might be!

I particularly want to use this CNC lathe for screwcutting so I am getting very frustrated...

Thanks in advance for any help or comments,

Brian

(In case it is relevant, I am generating toolpaths using Fusion 360 and the PlanetCNC turning post-processor. This appears to generate G33 commands for threading.)