Just restart Mach after you change it.
Hood

Thanks Hood. Just checked and it is already set at that.
GB

Did you try reducing your Vel and Accel a wee bit. If it is just on the top end of your motors capabilities  it may fail sometimes on certain moves.
Hood

Hi Hood,

Yep - I did that earlier - I reduced it by 10% and the accel by 20% - that was the question I was going to ask about the motor's capabilities at the top end. I know that steppers have good torque at low speed but really drop off at the top end. I ran the machine yesterday and had the same problems again on one certain move. Hair out time!! So, I'll go in the workshop now and turn the motors down by 25% and see if that cures the problem. I'll report back. Thanks for your continuing help!!

GB

Hi Again,
Just turned the motors down by 25% from original speed - were orig 2000mm/min - 5mm pitch screw - now at 1500mm/sec - Acceleration was 125mm/sec/sec now down to 105mm/sec/sec but still no different still stalls the motor momentarilly - looses almost 3mm on  and 8-9mm fast jog at one place only. Went through fine on one run then on second run the dreaded stall!!!! Is there a test I can do on the motors or some way of monitoring what is happening?
GB

Is it always at the same point on the axis?
Is it just one axis?
Hood

Hi Hood,

Yes - it is on the one axis and not necessarily in the same place, although it is a similar move on different programmes - and not in the same direction. Have checked and double checked everything mechanically and changed everything that can be changed electrically.

Now your last comments about stepper speeds/acceleration started me thinking - I related back to my mechanical days in motor racing and looked at what made engines stall -worked fine and accelerated good but with wheel spin on a quick take off - fitted fatter tyres and the clutch slipped - fitted heavier clutch - and the engine stalled. Ease on the quick take up on the clutch and cure the problem.
Acceleration! That must be the answer.
So I turned down the motors even further to 1200mm/min and the problem became rarer - only every so often. So acceleration it must be - turned the acc down to 85mm/sec/sec and the problem has dissappeared - then if it's just acceleration then the jog speed is not so critical - turned the jog speed up in increments and am back to 2000mm/min but with longer acceleration time and - wow! I just completed 6 jobs in the last hour!!!

Well done Hood - you've (it seems - so far!??) hit the nail on the head. I have a load of work to get on with on monday so I'll see what transpires. I'll let you know. And all the other bits I fitted or software setting that have been altered have all been to the good, so that's fine.

Many thanks for sticking with me on this one.
Regards,
GeoffB

Hopefully you got to the bottom of it
Hood

Hi Hood,

Wow, wow, wow and WOW!!!! Just done 2 days of milling with some complicated programmes - some taking a couple of hours to go through - and many fast jogs and not a beat missed! Looks like this is (dare I say it?) the final answer. Been looking at why the motor stalled onn the X axis and not the Y and thinking (and measuring) the saddle and gib lengths and the X one is about 15% longer than the Y, so the drag on the X would be marginally greater, so the motor was probably right on the edge of the acceleration and that one got it! Whatever, looks like I now enjoy going in the machine shop to do jobs (that have been mounting up!) instead of not daring to look at the miller, never mind working on it, in case it played up!

Anyway, many, many thanks for all your help.

GeoffB