What's new
What's new

VMC Multiple X axis / ballscrew problems

poxino

Aluminum
Joined
Jan 11, 2017
hello guys!

I tried to look through this forum, I couldn't find a similar thread about this.

So I bought another 2nd hand OKK VMC, Boxway , 16im control.
On the parameter's book, there is a section mentioning Softscale, I am not sure what that is and if is affecting the x-axis.
The machine configuration is head moves along the x-axis, and on z up and down, then the table moves on Y back and forward.

ATC, Spindle, and Z and Y axis seem quite good as well as the overall condition, but I think there are several problems with the X axis.

There were no noticeable noises until I machined a boss and came out of round by 0.004/0.005".
When the machine is off there was a play on the ballscrew , I could turn by hand a few degrees clockwise/counterclockwise.
Measured the backlash on X , it was with a clock and I made it around 0.004"/0.005".
We measured the slop on the ballscrew it was about 0.002".

I had my engineer in, and he thought Thrust bearings needed to be replaced, we replaced them with exactly the same ones and the problem was identical.

We then measured the housing bearings which seemed to be 0.008" deeper than the bearing thickness, we shimmed this and got almost no play/no slop on the ball screw.
I then measured the backlash and we are around 0.0025/0.003" which is still a lot, now Also, I am not sure why, perhaps because we shimmed the bearing, the machine is making a vibrating noise possibly coming from the motor, which it does not make me very comfortable to make further tests.
I am going to have the screw refurb, hopefully, this will fix the problem, but I am not totally sure.

To make this even more confusing, there is a high value on the x-axis backlash comp from the factory, something like 135, although these numbers they can be high numbers on higher resolutions motors/machines.
This machine has also several highspeed machining options like g05 p10000 and so on.

I have the original test report of the machine from the factory, and all the tests seemed between 0.00015/0.00025".

Also on the boss I machined, although there were big marks where the x-axis changed direction, the finishing looked still really good.

I hope someone can point me in the right direction.
 
Had similar problem with my Hitachi VMC..
Ended up finding an OEM ballscrew which we installed.
But, like you had high comp figures on x, dropped value to match Y ( which had zero slop) and holes became round. (y)

Noise from motor...everything back together right?
Shimming bothers me a bit. Assume bearings are retained by a cap? Did the screw turn ok after shimming or was it really tight?

Marks on part.....loose mechanical and/or high comp
 
Last edited:
Hello , yes everything seemed back toghether right.

Also, the visual screw condition is very good and shiny, I can not see any pitting at all , also the screw turns by hand really smoothly.

I am trying to have this screw refurb maybe, or do you think I need a new screw>

The cutter comp on the other axis is something like 10/20, and I would say they seem good on the table.
I am thinking maybe there could be something wrong on the motor bearing side of it???

It seems like there are multiple problems together which makes this more difficult to resolve.

It also make this vibrating noise (if I can say it this way ), only when works in G2/G3 , movements in rapids are fine, no noises, as well as movements with the handwheel, no noises.

Also, maybe another important detail , ( I haven't tried this on y and Z) , but the machine always have the same backlash amount, regardless I put 0 or whatever number on the backlash comp parameter.
 
Any chance that you took out .008 at the thrusts, had a .004 comp, and now your comp is making you worse?
(like Tech just said)

(you snuck in there, so that Q isn't as worthwhile)


To check lash in the screw, I have mag'd the incidator to the carraige, and put my probe down into thescrew thread, trying to stay as high as possible (more vertical than horizontal) and then turn the screw. Maybe even leave it stopped, and get a rigging bar to pry the axis one way, and then the other.


-----------------------

Think Snow Eh!
Ox
 
Hello,

thanks for the fast replies.

After shimming , the backlash on the screw is about 0.0001"/0.00015" (3/4 microns).
I can have that amount of backlash jump around 0.003" now on the table , regardless I put 0 or 135 on backlash comp parameter.
 
Never had to do it......... I thought I read where there was a separate feed and rapid setting of comp?
Might have been Fanuc? I may be wrong about this?
 
Yes on Fanuc control there is generally two separate parameters for feed and rapid backlash.
Screw turns very smoothly by hand.
 
There is, and I just had that up on my 'piter screen yesterday.


--------------------

Think Snow Eh!
Ox
 
Assign the measured backlash at cutting feed (A) in parameter No.1851 and that at rapid traverse (B) in parameter
No.1852.


If you look at the pic associated with that text in the manual, it shows it pretty good.
Not sure if that helps here tho?


ÇÇÇÇÇÇÇÇÇÇÇÇÇ
ÇÇÇÇÇÇÇÇÇÇÇÇÇ
ÇÇÇÇÇÇÇÇÇÇÇÇÇ
ÇÇÇÇÇÇÇÇÇÇÇÇÇ
ÇÇÇÇÇÇÇÇÇÇÇÇÇ
ÇÇÇÇÇÇÇÇÇÇÇÇÇ
ÊÊÊÊÊÊÊÊÊÊÊÊÊ
ÊÊÊÊÊÊÊÊÊÊÊÊÊ
ÊÊÊÊÊÊÊÊÊÊÊÊÊ
ÊÊÊÊÊÊÊÊÊÊÊÊÊ
ÊÊÊÊÊÊÊÊÊÊÊÊÊ
ÊÊÊÊÊÊÊÊÊÊÊÊÊ
ÇÇÇÇÇÇÇÇÇÇÇÇÇ
ÇÇÇÇÇÇÇÇÇÇÇÇÇ
ÇÇÇÇÇÇÇÇÇÇÇÇÇ
ÇÇÇÇÇÇÇÇÇÇÇÇÇ
ÇÇÇÇÇÇÇÇÇÇÇÇÇ
ÇÇÇÇÇÇÇÇÇÇÇÇÇ
ÊÊÊÊÊÊÊÊÊÊÊÊÊ
ÊÊÊÊÊÊÊÊÊÊÊÊÊ
ÊÊÊÊÊÊÊÊÊÊÊÊÊ
ÊÊÊÊÊÊÊÊÊÊÊÊÊ
ÊÊÊÊÊÊÊÊÊÊÊÊÊ
ÊÊÊÊÊÊÊÊÊÊÊÊÊ


Yeah, that didn't copy/paste too well...




4. DESCRIPTION OF PARAMETERS B–63010EN/01
90
1851 Backlash compensating value for each axis
[Data type] Word axis
[Unit of data] Detection unit
[Valid data range] –9999 to +9999
Set the backlash compensating value for each axis.
When the machine moves in a direction opposite to the reference position
return direction after the power is turned on, the first backlash
compensation is performed.
1852 Backlash compensating value used for rapid traverse for each axis
[Data type] Word axis
[Unit of data] Detection unit
[Valid data range] –9999 to +9999
Set the backlash compensating value used in rapid traverse for each axis.
This parameter is valid when RBK, #4 of parameter 1800, is set to 1.
More precise machining can be performed by changing the backlash
compensating value depending on the feedrate, the rapid traverse or the
cutting feed.
Let the measured backlash at cutting feed be A and the measured backlash
at rapid traverse be B. The backlash compensating value is shown below
depending on the change of feedrate (cutting feed or rapid traverse) and
the change of the direction of movement.



I was loading params in mine the last cpl of days and chasing a problem, and I noticed that the values in 1860 and 1861 (?) would change. But those params aren't even in the manual! I called Fanuc and they said that those will change and self fill, and to never mind those. LOL!

So this 1851 /1852 is right above where I was looking ... just happened to be.

I did git it going then...





----------------------

I am Ox and I approve this post!
 
Last edited:
Ok.... well..... if there is only a tenth or so backlash on the screw, no movement of the screw itself, back/forth... it's retained tight., and the X axis is not loose on the ways, and the Z axis is not loose on its vertical ways.....???...

there isn't anything mechanical left concerning lost movement.
Mechanical I can do, so I will bow to others with more knowledge on the Fanuc side.... :D
 
I haven't checked if the z axis is tight on the ways , but we checked the x axis and there was 0.0004" slop on the ways so he adjusted that.
I can check the Z axis but I don't think it would call that much difference.
This will be a difficult one to resolve I think
 
Hello guys!

I was away for while then came back.

So , nothing resolved so far.

We checked Z axis as , well , no movement.
I had the ballscrew assembly refurbished , re-balled, new thrust bearings as well.

I believe at this point there is no more mechanical backlash , however , when I try to test it with a clock , there is still 0.08mm backlash along x axis , which makes the machine unusable to me.

What seems more strange is this , after powering up the machine , if I try to jog the machine with the handle wheel regardless it's the smallest or biggest division the machine moves fine , I don't notice much backlash, maybe 0.01mm , maybe less , however, after moving 4/5 divisions back and forth, the machine starts to jump about 0.08mm when changing directions along x axis this seems very strange.

We then made a further test , my engineer swapped the wires on the amplifier on the back of the machine swapping x for y and viceversa, and that "jump" problem transferred to the Y axis , and X axis was working as it should.... so I believe there is no much wrong with motors/ballscrew/servo tuning and so on???

We sent amplifier for testing but testing company said amplifier is absolutely fine, we had infact no alarms.

Another strange thing is , the machine doesn't make any difference when changing/altering 1851 backlash parameters.

This will be another expensive and frustrating experience for me , if anyone has any suggestions please let me know.

I will keep this thread posted with updates.
 
and that "jump" problem transferred to the Y axis
Well...... if you swapped the electronics and the problem moved and X was OK........ its not mechanical.

Just talking out loud here.......lol......but........
When you change comp do the numbers change and remain at what you entered?
Or after power down/power up do they go back??
Sorry I cant help more.......
 
How about running the Ballbar test ? Lot of information in just few minutes.
I would run it twice on 2 different feed rates to get even more information.

Stefan
Cogito Ergo Sum
 
Check the jumpers on the amplifier. Compare the placement of them on the X and Y amplifiers. We had an issue with a machine jumping and making vibrations while the Y-axis was moving. Initially we thought bearings and ballscrews too, turns out two of the jumpers were in the wrong orientation and it wasn't set for the number of pulses the encoder uses. It was reading for more pulses than were actually being generated. If you send the amplifier out, they won't find anything because, it is working the way its designed to, just not the way it is supposed to with your specific machine.
 
Hello guys!

I was away for while then came back.

So , nothing resolved so far.

We checked Z axis as , well , no movement.
I had the ballscrew assembly refurbished , re-balled, new thrust bearings as well.

I believe at this point there is no more mechanical backlash , however , when I try to test it with a clock , there is still 0.08mm backlash along x axis , which makes the machine unusable to me.

What seems more strange is this , after powering up the machine , if I try to jog the machine with the handle wheel regardless it's the smallest or biggest division the machine moves fine , I don't notice much backlash, maybe 0.01mm , maybe less , however, after moving 4/5 divisions back and forth, the machine starts to jump about 0.08mm when changing directions along x axis this seems very strange.

We then made a further test , my engineer swapped the wires on the amplifier on the back of the machine swapping x for y and viceversa, and that "jump" problem transferred to the Y axis , and X axis was working as it should.... so I believe there is no much wrong with motors/ballscrew/servo tuning and so on???

We sent amplifier for testing but testing company said amplifier is absolutely fine, we had infact no alarms.

Another strange thing is , the machine doesn't make any difference when changing/altering 1851 backlash parameters.

This will be another expensive and frustrating experience for me , if anyone has any suggestions please let me know.

I will keep this thread posted with updates.
I have had a bad amp doing similar things although It wasn't throwing any alarms. Swapped the Amp and the problem went away. In my mind If the problem moves with the Amp. Well you've found your Issue.
 
Hello guys!

Thanks for the replies , I will pass these opinions/suggestions to my engineer, hopefully I will have other updates tomorrow.
 
Well...... if you swapped the electronics and the problem moved and X was OK........ its not mechanical.

Just talking out loud here.......lol......but........
When you change comp do the numbers change and remain at what you entered?
Or after power down/power up do they go back??
Sorry I cant help more.......
The parameters values change , however I don't see any real change in machine behaviour.

The values remain whatever I change after power down/power up
 








 
Back
Top