Wow!  68V to your stepper motor controller?  That seems a bit much.  Most drivers operate in the range of about 24 - 48V.  Using too high a voltage can create issues too.  From looking at earlier pictures you posted, it looks like we have similar stepper controllers so you definitely need to look at that.  Additionally, coming off of a transformer you are getting AC voltage.  There should be some sort of rectifier at least and regulators, etc. involved as well.  Recommended is to use a full DC power supply the puts out the required 24 or 48V DC.

Stephen "Highspeed" Kruse

P.S.  I know I'm a late comer to the discussion and only briefly perused through the thread so forgive me if I've missed something or repeating information already supplied.

EDIT:  I just saw the post that your stepper drivers are AC power rated, so this my comments may be totally irrelevant.

Thanks the the input mate, every comment helps trust me.

My drivers are rated between 36 - 8- VAC (although it doesnt mention a DC voltrage range of 50 - 110 VDC, so not sure if it operates in AC and DC)

http://www.leadshine.com/UploadFile/Down/MA860Hm.pdf

Ok, yes.  Mine are the M542 and utilize only DC at up to 50V.  Yours are rated quite substantially and can use either AC or DC looking at that document.  So that eliminates this as a potential source of the issue.  Just something I saw and am glad you had the documentation for it.

Stephen "Highspeed" Kruse

Hello RussH,

Your drivers are fine with this voltage, they are rated from 18 - 80VAC or 24V - 110VDC. Your mains voltage is a little higher then usual so your driver voltage is also a little higher but well within specs for your drivers. Pulses on the scope look fine, no worries about the ringing at the beginning of the pulse.

Try to reduce the current through the motors by changing the dip switch settings I posted earlier. Try with SW1: OFF, SW2: OFF and SW3: ON. This should reduce your current to 3.7A and peak current 4.45A.

Keep your acceleration low to start with and see what happens. If this works fine, increase your acceleration and speed back to the normal settings step by step until you feel OK with it.

G21

Thanks, I will give it a go.

Thought I would mention, I found a label on one of the steppers yesterday. They have a part number of 86bygh450b-06d-15j
Not sure it this helps at all.

Copied and pasted your motor numbers in ebay and came across another CNC'er loosing steps with these motors it appears his problem was mechanical, have a look at his thread although he doesn't say he has solved the problem
http://www.cnczone.com/forums/mach-software-artsoft-software-/154503-z-axis-losing-steeps-2.html

Hi Jim,

I took the motor and coupling off the ball screw today, and ran the spindle head up and down its slides 3 times by manually turning the ball screw. It was fairly easy to turn (could do so with just a finger grip), and didnt feel any sudden change in resistance during its travels.

Any update here? Been quite a long time now.

Curious if you figured it out.

G21