Hi everyone,

I'm new to CNC machining and a friend and I have bought a chinese cnc machine from ebay ( like this one http://www.ebay.co.uk/itm/2907045318...#ht_2396wt_934 from the same seller) I don't really know exactly what model it is, there are no numbers on it or anything (I know, I know apologies for being a useless n00b)

I've been using the machine on and off to make various bits and pieces and am running into problems with the z axis, every now and again (but often enough to be problematic!) the Z axis will ram down by about 10mm, usually snapping the bit and wrecking the piece. I have run the same g-code and it has worked fine, so I am assuming it's not a problem there.

I had a look through the forum and found this post :
www.mycncuk.com/forums/showthread.php/1395-
Z-Problem but it's from 2009 and wasn't resolved. He was having the same problem as me.

I've tried tightening the coupler which seemed pretty tight anyway, so I am assuming the motor is over running for some reason.

I guess by looking around the forum that it's probably the controller? The problem is I really don't know what I am looking for to test/replace/fix it. I don't even know which one of the controllers it is! Is it a controller or a driver that I mean (there are 3 of them with dip switches on)?

Any help and general advice (links to other posts etc.) would be very gratefully received. I can't leave the machine to do its thing without hovering a few mm from the stop button!

Thanks.