UNSTABLE Z-AXIS

[bestrada11]

LATELY I HAVE BEEN NOTICING A HEAVY FRONT EDGE OF CUT WHEN FACING OVER LARGE RUNS OF X SIMILAR TO AN ADJUSTABLE HEAD OF A KNEE MILL BEING OUT OF ADJUSTMENT. BUT SINCE I HAVE NO ADJUSTMENT ON MY HEAD MYSELF AND THE GENTS AT MILLTRONICS WERE ASSUMING SOME KIND OF WEAR ON THE GIB. BUT ITS GOTTEN PROGRESSIVLY WORSE STARTING OUT AT BARELY NEGLEGIBLE TO SOMEWHERE AROUND 5 THOU. (.005) SO TODAY IM RUNNING A FACING PROGRAM ON A LARGE FLAT PANEL AND WATCHING THE BALL SCREW AND IT IS EVER SO FAINTLY JUMPING IN ROTATION. SO WHEN I PUSH UP ON THE QUILL I FEEL THE SERVO TRY TO COMPENSATE KINDA TWITCHY. AND WHEN RUNNING THE FACE PROGRAM ALSO KINDA TWICHY. THERE IS A DULL WHINE COMING FROM THE SERVO CARDS. THE WHOLE TIME I HAVE HAD THE MILL I ASSUMED THIS IS NORMAL. BUT AS I LISTEN VERY CAREFULLY THE TWITCH OF THE BALL SCREW CHANGES THE SOUND OF THE WHINE. I DONT KNOW IF THIS IS ONLY THE Z CARD MAKING THE SOUND OR IF ITS COMING FROM ALL EQUALLY BUT ONLY THE Z IS CHANGING THE SOUND WITH THE TWITCH. THESE ARE SERVO DYNAMICS SD1525-10 CARDS AND HAVE ADJUSTMENT POTS AVAILABLE. CAN SOMEONE TELL ME IF THIS IS SOMTHING I CAN "TUNE IN"

[Brian L]

Search the net for a manual for your drives..... mine are slightly different, but I found the manual online. Yes, they can be tuned... the procedure is detailed in the manual, Milltronics should also be able to send you the documentation for the procedure too.

[70cyclone]

i would pull the motor brushes and clean and/or replace them
you can also swap cards and see if the 'twitch' moves to another axis

[bestrada11]

ok i took the prior advice. i also am working with mark at milltronics and he has sent me some very valuble info on cleaning the tach brushes and armature. heres what has happened so far and where im still at i will list all major steps and advancements in info buy number.
1. swapped y and z axis servo cards. this did nothing for isolating the problem the y is still ok and the z still has the twitch while machining.
2. i noticed that the twitch is directly linked to a high pitch ring that is emitted from the machine. this ring is only on when the servos are activated or energized. so when the E stop is pushed the servo cards or off and so is the sound. this sound is also coming from the motor itself.
3. mark at mill tronics sent me a write up on cleaning the tach of the motor from the back cap. i followed this procedure and the sound was reduced but not eliminated. also the twich still exists.
4. after all the above steps, i ran a facing program on my fixture plate im making. and the twich i have noted is directly connected to a change in force put upon the quill so basically over a long stretch of .010 removal of aluminum the position is fine but mid run my end mill passes over a stainless steel insert that puts a higher load on the spindle the ball screw for the z axis starts to twitch like the servo amp is fighting to keep it in position. i first thought that maybe it was just tool drift around the stainless insert but after the mill had passed the insert the drive continued to compensate(?) and the twitch is visible in the depth of cut.
5. i have a procedure for adjusting "following error" so basically it calls for writiung a program for one axis running at 100 feed rate and to moniter the error display on the screen. i have not done this adjustment that calls for the error to be at .050 which mine is at .074 because there is a part of the procedure im not sure of where it asks to zero and then reset the gain velocity parameter im not sure exactly what steps to follow while doing this and running the 100 feed rate program and adjusting the servo card.

im sorry this is so much info im just trying to give all the stuff i have at my fingertips on the hope that someone can point me in the right direction!!!

ok i took the prior advice. i also am working with mark at milltronics and he has sent me some very valuble info on cleaning the tach brushes and armature. heres what has happened so far and where im still at i will list all major steps and advancements in info buy number.
1. swapped y and z axis servo cards. this did nothing for isolating the problem the y is still ok and the z still has the twitch while machining.
2. i noticed that the twitch is directly linked to a high pitch ring that is emitted from the machine. this ring is only on when the servos are activated or energized. so when the E stop is pushed the servo cards or off and so is the sound. this sound is also coming from the motor itself.
3. mark at mill tronics sent me a write up on cleaning the tach of the motor from the back cap. i followed this procedure and the sound was reduced but not eliminated. also the twich still exists.
4. after all the above steps, i ran a facing program on my fixture plate im making. and the twich i have noted is directly connected to a change in force put upon the quill so basically over a long stretch of .010 removal of aluminum the position is fine but mid run my end mill passes over a stainless steel insert that puts a higher load on the spindle the ball screw for the z axis starts to twitch like the servo amp is fighting to keep it in position. i first thought that maybe it was just tool drift around the stainless insert but after the mill had passed the insert the drive continued to compensate(?) and the twitch is visible in the depth of cut.
5. i have a procedure for adjusting "following error" so basically it calls for writiung a program for one axis running at 100 feed rate and to moniter the error display on the screen. i have not done this adjustment that calls for the error to be at .050 which mine is at .074 because there is a part of the procedure im not sure of where it asks to zero and then reset the gain velocity parameter im not sure exactly what steps to follow while doing this and running the 100 feed rate program and adjusting the servo card.

im sorry this is so much info im just trying to give all the stuff i have at my fingertips on the hope that someone can point me in the right direction!!!

ok i took the prior advice. i also am working with mark at milltronics and he has sent me some very valuble info on cleaning the tach brushes and armature. heres what has happened so far and where im still at i will list all major steps and advancements in info buy number.
1. swapped y and z axis servo cards. this did nothing for isolating the problem the y is still ok and the z still has the twitch while machining.
2. i noticed that the twitch is directly linked to a high pitch ring that is emitted from the machine. this ring is only on when the servos are activated or energized. so when the E stop is pushed the servo cards or off and so is the sound. this sound is also coming from the motor itself.
3. mark at mill tronics sent me a write up on cleaning the tach of the motor from the back cap. i followed this procedure and the sound was reduced but not eliminated. also the twich still exists.
4. after all the above steps, i ran a facing program on my fixture plate im making. and the twich i have noted is directly connected to a change in force put upon the quill so basically over a long stretch of .010 removal of aluminum the position is fine but mid run my end mill passes over a stainless steel insert that puts a higher load on the spindle the ball screw for the z axis starts to twitch like the servo amp is fighting to keep it in position. i first thought that maybe it was just tool drift around the stainless insert but after the mill had passed the insert the drive continued to compensate(?) and the twitch is visible in the depth of cut.
5. i have a procedure for adjusting "following error" so basically it calls for writiung a program for one axis running at 100 feed rate and to moniter the error display on the screen. i have not done this adjustment that calls for the error to be at .050 which mine is at .074 because there is a part of the procedure im not sure of where it asks to zero and then reset the gain velocity parameter im not sure exactly what steps to follow while doing this and running the 100 feed rate program and adjusting the servo card.

im sorry this is so much info im just trying to give all the stuff i have at my fingertips on the hope that someone can point me in the right direction!!!

[ZZZZ]

Try the Following Error procedure you got from Mark, .074 is too much. It would be a good idea to do all 3 axis while you are at it, if Z is that far off, X and Y may be off too.

The Gain Velocity Parameter change is only necessary on Cent 6 (grey cardcage) machines, if yours is a Cent 5 (black cardcage) machine, ignore that part of the procedure.

If you have a Cent 6, get into Level 3, go to the end of the AXIS parameters, find the Gain Velocity Parameter, note the values there, set them to zero, and escape back to the Main Menu. Home the machine to make the changes active, and then do the Following Error tests. Re-set the Gain Velocity Parameters back to their previous values when your are finished.

I'd also check the backlash to see if the axis may be floating a little.

[bestrada11]

Good info ill do that and when I'm done I will check the backlash I'm assuming I do this with an indicater and dependant on what I find what do I do? Is it the backlash compensation? I just did that at work on pc based knee mill we have it just basically compensated on directional changes for backlash.

[ZZZZ]

Use the procedure you got from Mark, .074 is too much.

The Gain Velocity Parameter change is necessary only on the Cent 6 (light grey cardcage) machines. If you have a Cent 5 (Black cardcage), ignore that part of the procedure.

If you have a Cent 6, get into Level 3, go to the end of the AXIS parameters, find the Gain Velocity Parameters and note their values, Change them to zeros and escape back to the Main Menu. Home the machine to make the changes active and do the Following Error procedure on all 3 axis. Re-set the Gain Velocity Parameters back when you are finished.

Now would be a good time to check and re-set Backlash as well.

[bestrada11]

Right but u keep mentioning backlash and mark never supplied procedure for backlash. So I'm wondering what u were asking me to do. I was asking if it was basically what I had done at work?

[ZZZZ]

Ask Mark to send you the document Procedure to set or adjust backlash.doc for the technique.

[bestrada11]

Can you suggest any other documents it would be good to have I'm compiling a pretty informative manual for this machine.