Fasal z- axis stutter

pcasanova · Jun 30, 2020

3016 97 ac fadal. powered up about a month before was used last. cs the machine and everything seemed normal. got a tool and when the spindle lowered over a tool the z- had
what seemed like a mechanical stuttering as it went down over the tool. still got to the tool no alarms. so jogged up and down .01 dial set and jogging smoothly no problems in either direction. but spinning the wheel fast down and stuttering would show. spin up no issues.

A little more background, the machine is on a phaseperfect. A few months ago I turned the rapids to 100% always had them set at 50%. and when the rapid on z happened the machine wasn't happy with it threw an alarm and the z position was off. cs the machine and seemed normal. It seemed to run normal after that just set back to 50% rapid, I figured a power issue and went on with life.

It was late but had a spare amp so I tried it and nothing changed. Oiled the z just to make sure it was a lubrication issue. the thrust bearing was replaced about 2 years ago, the tech checked the ballscrew and said it was fine, work had replaced it not even a year before deciding to replace the machine.

Anyone ever deal with this? trying to figure mechanical or electrical?

Bobw · Jun 30, 2020

Its a gain setting on either the axis control card or the amp itself.

Its in the manual on how to do it, and what following error you are
shooting for. Though the following error they say to shoot for
doesn't always seem to work, or you can't always get there.

macds · Jun 30, 2020

Or maybe the thrust bearings are shot again?
My buddy has a 4020 that shuddered like a bastard in Z. We did the thrust bearings, and it cleaned it right up.

Bobw · Jun 30, 2020

macds said:
Or maybe the thrust bearings are shot again?
My buddy has a 4020 that shuddered like a bastard in Z. We did the thrust bearings, and it cleaned it right up.

Had that happen on a little POS accuslide on the Z. Smooth as silk in one direction, and thought
the machine was going to jump off the floor in the other direction. After about 5 minutes of that
it turned into a one way bearing.

pcasanova · Jun 30, 2020

Bobw said:
Its a gain setting on either the axis control card or the amp itself.

Its in the manual on how to do it, and what following error you are
shooting for. Though the following error they say to shoot for
doesn't always seem to work, or you can't always get there.

ok first thing I checked bl, was set at 8 and had to change by 3 to 11 to comp out. then ran the program in the procedure for setting
the amp and the following error was 302 the procedure called for. So guess looking at the thrust bearing. with a .0011 of bl, should I
just get a new screw assembly with the nut?

Delw · Jul 1, 2020

pcasanova said:
3016 97 ac fadal. powered up about a month before was used last. cs the machine and everything seemed normal. got a tool and when the spindle lowered over a tool the z- had
what seemed like a mechanical stuttering as it went down over the tool. still got to the tool no alarms. so jogged up and down .01 dial set and jogging smoothly no problems in either direction. but spinning the wheel fast down and stuttering would show. spin up no issues.

A little more background, the machine is on a phaseperfect. A few months ago I turned the rapids to 100% always had them set at 50%. and when the rapid on z happened the machine wasn't happy with it threw an alarm and the z position was off. cs the machine and seemed normal. It seemed to run normal after that just set back to 50% rapid, I figured a power issue and went on with life.

It was late but had a spare amp so I tried it and nothing changed. Oiled the z just to make sure it was a lubrication issue. the thrust bearing was replaced about 2 years ago, the tech checked the ballscrew and said it was fine, work had replaced it not even a year before deciding to replace the machine.

Anyone ever deal with this? trying to figure mechanical or electrical?

bad axis motor can do it also as well as your drives not being tuned for the correct ball screw.
I run power company 3 phase, however if your convertor isnt putting out correctly that can cause it as well.
one way to find out is just rapid one axis at a time at 100%

do the 45 degree test at different feed rates and make sure your following errors are the same and dont bounce. doesnt make any difference what the number is as long as they all match and DONT bounce alot. 1 or 2 is ok anything over that tune it or replace the resolver.

macds · Jul 1, 2020

pcasanova said:
ok first thing I checked bl, was set at 8 and had to change by 3 to 11 to comp out. then ran the program in the procedure for setting
the amp and the following error was 302 the procedure called for. So guess looking at the thrust bearing. with a .0011 of bl, should I
just get a new screw assembly with the nut?

You almost need to pry up on the head to check actual lash in the screw\thrust bearings.
Bring the head down to the table with an indicator in a drill chuck on the table. Youll likely have slop in the head straps thatll show this way as well.... how does the spindle tram to the table?
Couple blocks of wood on the table a pry up on the head casting.
But Im pretty sure youll see way more than .0011.

Is this an extended Z machine? Is the motor coupling ok?

pcasanova · Jul 1, 2020

Delw said:
bad axis motor can do it also as well as your drives not being tuned for the correct ball screw.
I run power company 3 phase, however if your convertor isnt putting out correctly that can cause it as well.
one way to find out is just rapid one axis at a time at 100%

do the 45 degree test at different feed rates and make sure your following errors are the same and dont bounce. doesnt make any difference what the number is as long as they all match and DONT bounce alot. 1 or 2 is ok anything over that tune it or replace the resolver.

I did think motor resolver, but z+ zings away, just the z- direction. turned the rapids to 25% to calm the z- movement and only when it lowers over the tool is it shuddering, guessing that part of the cycle doesn't look at machine over rides.
I did the test program fadal had for the procedure and all x,y,z were pretty spot on at 302, it would randomly deviate by to 303 here and there, and can rapid x y no issues.

macds - I'm assuming the mount and tram are in. again a month ago when I last used it, it ran fine. no it's not extended.
but I talked to the plant manager and I was mistaken on the ballscrew replacement was done like 5 years ago. but the tech who put everything together showed me the ball nut and still had preload so he said it was fine, then showed me the thrust bearing (which luckily i did have on hand) was bad so he replaced it. they did check the tram and ran a dial and it didn't vary over +/- .0005 over the entirety of the table. I'll check the thrust bearing tomorrow, but would there be a chance the bearing would hold height but lock up in the other direction?

macds · Jul 1, 2020

pcasanova said:
I'll check the thrust bearing tomorrow, but would there be a chance the bearing would hold height but lock up in the other direction?

Check the tram by putting indicator in spindle and clocking table, like squaring head on bridgeport.
Yes, the head weighs quite a bit, so itll hold height (until you cut, or apply upward force with a pry bar) then it'll float. Make sense?

pcasanova · Jul 14, 2020

Just to follow up figured out the problem. installed new ballscrew assembly same issue, swapped y and z servo and issue went away. didn't bother to even mount the motor to the y to see if the issue followed. Now rebuild the bad motor or get a new?

triumph406 · Jul 14, 2020

pcasanova said:
I did think motor resolver, but z+ zings away, just the z- direction.

If it has resolvers then it's a DC machine, so could it be a DC machine rebuilt in 97?

If it's a DC machine then what your describing could be caused by a dirty tachometer. it's about 1-2" past the resolver. Clean it's commutator and it will be ok.

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