Hello guys.
Some answers here.. 8 wires to the round Servo/stepper, wired in 4 pairs I notice.

Some pics attached

Ooop that was to big for my screen

You have stepper motors.   Can't spot your drives though.

Thanks fdos, that discounts the accumulation of error pulses causing it, and leaves me with good old mechanical backlash on the x axis, and it doen't matter what the drives are.

Photo attached of screws at base of z axis

Cheers

Looks like you have standard Acme screws.   If there are two nuts on each you might be able to take out some of the backlash.  There are ways of doing it with one nut too.

Sometimes the drive does matter, some are sensitive to direction change timing.   

Where in the uk are you.  I assume you are over here!

You could check to see how much backlash you have either with a dial gauge or even a fine pen  mounted on you z axis.   you appear to have a fair bit of slop there, so that methos would show it.

Wayne...

Sunny Buxton in Derbyshire Wayne.

Art and Hood have suggested ways of measuring the backlash, which I have yet to do.
Considering, like you say, the amount of backlash, I expected to be able to feel it in the machine, but rocking the thread from the end does seem to move the zaxis instantly. this leads me to want to investigate the stepper/thread interface. I seem to remembr reading years ago that things like a short length of tubing can be used to form a crude clutch in case of a crash, and I am wondering if there is something like this that has malfunctioned. Either this or there is some direction change timing problem like you say. Also there is the problem of apparently losing steps quite badly,...I'm starting to think mechanical rathr than electronic.

thanks for your help.

Where are you Wayne?

James,
I'm down on the Notts Derby border M1 J25.
Do you want me to pop up and take a look one night?

John S.

I far enough away in Poole dorset

Also check the bearings at the end on the screw,  backlash can be created there.   Normally these bearings are back to back angular contact bearings with some preload of them.

Wayne..

John S Thanks, thats a fantastic offer.
I'll have a go myself before I ask you to put on your snowsuit and head up into the hills. -The suggestions from the guys on the forum have given me loads of leads, so I'll follow them up as far as I can.

thanks again.

Jim

John I need my lathe finished if you are looking for work

If you guys can't find the problem try sherline mode. this will give a very long step pulse and could help the drive (Whatever they are)