Thread: Z axis spindle load problem

So my old QT-8 is almost rebuilt, she's running fine making parts.

Still have one nagging issue.

The Z axis servo load is always at least 20%, if it is moving at all it's at least 50%, spikes to over 150% if it's in rapid, cutting it's 20% to 200%, on and off. Does not seem to matter if it's a .05 OD turn in aluminum or a 1" drill.

The axis moves fine with the power off I can turn the screw with two fingers. Backlash is .0002, as small as I can reasonably measure. The drives x and z were just repaired at Mitsubishi last month it did not fix this issue which I've had since I got the machine.

The z axis resolver has already been replaced as well.

Any ideas?

Is there some way I can just turn the load meter off? I'd settle for that.

Nervis, I can only give you a few reassurances, and maybe a few suggestions.

First we are running two mazaks, one always has 35% load on the Z, thats the mill, no counter weights.

Our lathe, a QT-20 normally spikes 150-200% on rapids. Also last summer while I was on vacation our lathe suffered a nice crash. Realigned the turret, the headstock and found the X to be out from the Z about .003 over 4 inches, so we started ripping stuff apart to make an attempt to get them a little more square. After our attempts, we did get it within a thou over 4" but the static load on the X went from 2-3% to 5-7%. I'm sure the slides are now not perfectly(I hate that word, it makes me sound like a carpenter) parallel, but she still runs like a champ, and i could still turn the ballscrew VERY easily by hand.

One other possibility, on our Fadal, we were getting a large following error and a nasty hum out of the X axis at idle. A few turns on the pots on the driver board and it calmed it down, now I don't know if the Mazaks are the same or not, they really just don't break that often, but it might be something to consider. The motor was just fighting itself to hold position.

good luck.

Thanks for the reply. I'll tweek on the gain pot a bit tommorw and see what happens. I do also get a whine now and again from the motor like you describe.

trs-50B droop + gain
go to
diagnosis screen
hit "adjust" soft key
droop
should be as close to -0- as you can get it with axis at rest
set droop with "offset" variable resiter
found in a row of about 5 vr's towards bottom of drive.
gain
with machine in "jog mode" --button with up and down squigly line between home and handle buttons
and feed set to about 150%
move axis back and forth watching gain value,
should be as close to 33 as you can get it when axis is moving
adjust gain with variable resister marked "gain" in same row of vr's as droop vr
disregard change in droop value when axis is moving.
the adjustments on both these vr's are so small that if you actually feel the thing turn you've adjusted it a mile.
not sure if this will help your problem
have you ever megged motor
may be dirty and need sent for cleaning
i have also been told by mazak that these load meters can get out of adjustment
not sure how to correect that problem
a peck cycle on a drill will spike these load meters to the moon
one big suspect on an older machine for axis binding is the way covers.
send the machine home what's the load
now in handle .001 move the machine of home just a few clicks
does load meter drop.
look for bent or damaged cover components

Whippin boy, Thanks for all that advice I'm going to try it all. Except the "megged" motor....what does that mean?

My droop fluctuates from 20-21 back and forth at rest.

Also the motor is dirty as hell. Lots of gooey 20 year old coolant and hydraulic oil on it. I did not think goop on the outside would make a difference.


A while ago you mentioned a place that could repair and clean a motor, was that Reid machine?

Is it difficult to remove that z axis motor?


Dave

dirt on outside presents mostly a cooling issue
it's not a good thing but
i don't believe it would gives problems discribed.
driesilker elec.--630-469-7510
are factory authorized mits repair facility
they have the stuff to completly set up your servo
i'm sure there are others
i would definatly try to get that droop and gain adjusted.
what i have been told is motors like this will build up junk inside that will lower there insulation value (resistance to ground)
that is what a megger checks
any motor shop can check this but not all are set up to properly check your resolver and motor setup
link below gives some info on "meggers" and also some availible models
http://www.mcmaster.com/ctlg/DisplCtlgPage.asp?ReqTyp=CATALOG&CtlgPgNbr=690&Ctl gEdition=&sesnextrep=610222009279958&ScreenWidth=1 024&McMMainWidth=812&ToolsetID=ToolPageFlip&Toolse t Act=
pulling -z- motor sucks but is easy
2 canon conectors
four shcs holding motor itself
and a flexible coupling that connects motor shaft to ball screw
loosen all the 10mm(?)hex heads on couple and give it a little rap to break compression rings loose
loosen couple first
remove 4 shcs
it's in your lap
the suck part is where its at

while your in there you may want to look at thrust bearings.
not cheap but good time to replace if needed

OK, got the gain and droop adjusted as you said. My z axis load does not go above about 150% now running the same program.

Thanks for the help!

Dave