Hi Nick,

Many thanks for your thoughts - certainly something along those lines would be a good plan I think.

I guess I was just sceptical that this tweaking of settings should be required for a C7 screw. Maybe what I have are out of spec - or indeed maybe they aren't actually C7 screws? The guy I acquired the machine from just remembered that they were from Marchant Dice and that they were "not precision ones". Marchant Dice currently only go down to C7, so I have just emailed them to see if they have ever supplied lower spec screws like C10. If that was the case then I have an explanation, and the steps per mm tweaking could be a legitimate way forwards.

We'll see what Marchant Dice have to say....

Cheers
Graeme