Progress! You may remember a while ago I tried extending the encoder cables with some CAT5 cable I bought which turned out to be the cause of an earlier issue. I used the same cable to make up the RJ45 cables that link the encoders to the drives.

I have no idea why I didn't replace these earlier when I had the other issue, but swapping them out for some bought patch cables has stopped the motor juddering..

I stripped back the outer insulation of a piece of the cable from the reel and every now and then there is a break in the conductor but the insulation remains in tact! which I can only assume was enough to make a contact when I tested the cables but mounting it on the machine must have given it an intermittent connection.

Now back to the tuning!