squeezing the last bit of accuracy on a BP V2XT cast Iron
Close
Login to Your Account
Likes Likes:  0
Page 1 of 3 123 LastLast
Results 1 to 20 of 44
  1. #1
    Join Date
    Jan 2007
    Location
    Central FL
    Posts
    906
    Post Thanks / Like
    Likes (Given)
    8
    Likes (Received)
    22

    Default squeezing the last bit of accuracy on a BP V2XT cast Iron

    This here is a retrofit and I did all the new electronics with machmotion controller 750 Watt closed loop servos. They have a calibration app where I put a DTI in my quill set it to zero off a 4" gauge block and then command a move( 4.007"), then I input into the screen what the move actually was, and that tells the machine how many steps per inch on that axis. Servos have like 10,000 PPR or something like that and between lead pitch and pulley ratio 10 rotations equals an inch. Now my problem is that throughout the axis' I have different steps per inch. One spot in X it can be 100,070 in another it can be 100,550 and so on and so on. OK, the machine is from 1991 ( last 5 years sitting in my garage collecting dust), but it is supposed to have NSK ballscrews and I also changed the regular bearings some stupid maint guy threw in there to thrust bearings when I originally retrofitted it back 5 years ago. I had decent accuracy back then only electronic problems, now with the machmotion system, electronics are better, but mechanically speaking I am getting different steps per throughout my axis motion. I haven't even started on backlash. ON Z axis I am getting like .0025" difference between 2" move and 4" move. driving me nuts. I was going off a parallel laying across the table. If I get screw mapping on this thing, you guys think I can rely on the knee to go down .25" increments and map that in the controller. Thanks for all the help.
    Sincerely,
    C. Wizman
    Last edited by madmachinst; 07-14-2021 at 02:01 PM.

  2. #2
    Join Date
    Aug 2014
    Location
    bainbridge island
    Posts
    1,411
    Post Thanks / Like
    Likes (Given)
    307
    Likes (Received)
    350

    Default

    The variability sounds more like backlash.

    Variations in friction,etc, change where the table settles within the backlash. (Which isn't a hard value either, but depends on how hard you push on the screw)

  3. #3
    Join Date
    Jan 2007
    Location
    Central FL
    Posts
    906
    Post Thanks / Like
    Likes (Given)
    8
    Likes (Received)
    22

    Default

    But I am only going in one direction. Zeroing the DTI on a gauge block by jogging onto it. commanding the app to move the axis .007" beyond the length of the gauge block and entering that dimension I get. say DTI shows only .0055 after zero then I enter 4.0055 ( If zeroing on 4" gauge block). So my question is how has that got anything to do with backlash? I am already taking up backlash when I jog onto the gauge block.

    Now, regarding variations in friction and where the table settles in backlash. You think with an arduous warm up cycle and my manually activating the lube pump while that is happening that will help? Been so long since I took out the ball-screws, but do the ball-screws get their lube from the lube pump or do I have to move the covers and lube them manually?

  4. #4
    Join Date
    Jun 2008
    Location
    VA
    Posts
    809
    Post Thanks / Like
    Likes (Given)
    210
    Likes (Received)
    326

    Default

    Might be a servo tuning issue, any overshoot would have that effect if it was less than the total mechanical backlash. How much backlash do you have? I'd look at your tuning, the drives on my retrofit have a utility that will plot the command vs position and show the curve resulting from a step input, a little overshoot is ok as that is required for critical damping (min settling time) but if you have mechanical issues being underdamped might work better but can introduce following errors when profiling.

  5. #5
    Join Date
    Mar 2006
    Location
    Vershire, Vermont
    Posts
    2,760
    Post Thanks / Like
    Likes (Given)
    1929
    Likes (Received)
    919

    Default

    Maybe cosine error in DTI readings?

  6. #6
    Join Date
    Jan 2007
    Location
    Central FL
    Posts
    906
    Post Thanks / Like
    Likes (Given)
    8
    Likes (Received)
    22

    Default

    Quote Originally Posted by Nmbmxer View Post
    Might be a servo tuning issue, any overshoot would have that effect if it was less than the total mechanical backlash. How much backlash do you have? I'd look at your tuning, the drives on my retrofit have a utility that will plot the command vs position and show the curve resulting from a step input, a little overshoot is ok as that is required for critical damping (min settling time) but if you have mechanical issues being underdamped might work better but can introduce following errors when profiling.
    these are autotuned servos. seller Just told me to hook em up and let the servos do their thing. Now I am fixing on writing a program where the axis make the table move in diamond motion for a while as the diamonds get smaller and smaller to try and get the axis warmed up. If there were any buttons I should press on the drivers to get the set up to autotune would have been great to run that now. I'll get back to them on that and pray I don't get back a stupid response from them. I paid the bigger bucks expecting service otherwise I could have bought from Arturo.

  7. #7
    Join Date
    Jan 2007
    Location
    Central FL
    Posts
    906
    Post Thanks / Like
    Likes (Given)
    8
    Likes (Received)
    22

    Default

    Quote Originally Posted by neilho View Post
    Maybe cosine error in DTI readings?
    will reinstall the DTI and try to keep the stylus as close to parallel to gauge block as possible. Thanks guys, keep em coming.

  8. #8
    Join Date
    Jan 2007
    Location
    Central FL
    Posts
    906
    Post Thanks / Like
    Likes (Given)
    8
    Likes (Received)
    22

    Default

    after running table on warmup program for 50 minutes I moved the covers on the ballscrews and they were shiny and it didn't seem they were wet/lubed. is removing the table a necessity to check those lines and see if there is a clog? Y axis I take it I just remove the box holding the motor pulleys and belts and then the way covers come off.

    Also seemed like my X axis belt starting to tear. I'll post pics and see if you guys think it can last a few more miles.

  9. #9
    Join Date
    Jun 2008
    Location
    VA
    Posts
    809
    Post Thanks / Like
    Likes (Given)
    210
    Likes (Received)
    326

    Default

    Usually it’s the metering orifices than clog, you can take the oil lines off the manifold and see if oil comes out. Both of my boss and the v2xt had bad metering orifices. They can’t generally be unclogged and are $16ea from McMaster, you can probably find them cheaper. You have to unhook the lines from the ballnut and blow them out. If those are clogged, the ways are probably also not getting oiled and that means taking the table off…

  10. #10
    Join Date
    Jan 2007
    Location
    Central FL
    Posts
    906
    Post Thanks / Like
    Likes (Given)
    8
    Likes (Received)
    22

    Default

    BTW here is the progress I have been making in video, I really [email protected] @ making videos, but that is what it sounds like and runs like. All observations highly appreciated.
    https://youtu.be/9gpITCJxcKo
    https://youtu.be/97ytxrFVkQs

  11. #11
    Join Date
    Jan 2007
    Location
    Central FL
    Posts
    906
    Post Thanks / Like
    Likes (Given)
    8
    Likes (Received)
    22

    Default

    pictures of ball thread. I went back and forth with table a few times and hit lube, but the screws in my opine seemed dry. Here are pics. The cover for the crews OTOH were soaking. Worse case scenario if I need to make some parts on this thing before I can afford to send it over for planned on returcite, rescrape, rebearing reballscrew, and re do lube system. I'll just move table over to one side completely push the cover aside give it a lube with some kind of spray product, then do the other side. Suggestions on what I should use? Every 2 hour will be enough?
    Attached Thumbnails Attached Thumbnails 1-oil-trough.jpg   2-torn-belt.jpg   3-oil-screw-cover.jpg   4-overall-screw.jpg   5-overall-screw.jpg  


  12. #12
    Join Date
    Jan 2007
    Location
    Central FL
    Posts
    906
    Post Thanks / Like
    Likes (Given)
    8
    Likes (Received)
    22

    Default

    rest of pics.
    Attached Thumbnails Attached Thumbnails 6-screw-specific-point.jpg   7-screw-specific-point.jpg   8-ballnut.jpg   9-ballnut.jpg  

  13. #13
    Join Date
    Jan 2007
    Location
    Central FL
    Posts
    906
    Post Thanks / Like
    Likes (Given)
    8
    Likes (Received)
    22

    Default

    Quote Originally Posted by neilho View Post
    Maybe cosine error in DTI readings?
    I can rule that one out. have the needle almost perfectly parallel to gauge blocks.

  14. #14
    Join Date
    Jan 2007
    Location
    Central FL
    Posts
    906
    Post Thanks / Like
    Likes (Given)
    8
    Likes (Received)
    22

    Default

    Quote Originally Posted by johansen View Post
    The variability sounds more like backlash.

    Variations in friction,etc, change where the table settles within the backlash. (Which isn't a hard value either, but depends on how hard you push on the screw)
    Now, say I took a torque wrench 1/4" drive and tried to rotate the ballscrew to move the table. I understand from prototrak they say no more than 15 in lbs. So basically if it takes less than that to smoothly move my axis', You think I can safely rule that out? At this point I just want to know what is causing my problems. if I get more than 15 in lbs, then I'll start loosening stuff. Now, before the servos where on there I could rotate the axis' by wrist muscles only ( me no tough guy). I am wondering when I reintroduced the servos maybe the belts ended up getting too much tension? Had to redesign servo adapter plates, maybe that did it?

  15. #15
    Join Date
    Mar 2006
    Location
    Vershire, Vermont
    Posts
    2,760
    Post Thanks / Like
    Likes (Given)
    1929
    Likes (Received)
    919

    Default

    You mention that the x axis belt is tearing. I've known that to cause inconsistent angular spindle position on a lathe. Or are you having problems with the y axis, too?

  16. #16
    Join Date
    Jan 2007
    Location
    Central FL
    Posts
    906
    Post Thanks / Like
    Likes (Given)
    8
    Likes (Received)
    22

    Default

    Quote Originally Posted by neilho View Post
    You mention that the x axis belt is tearing. I've known that to cause inconsistent angular spindle position on a lathe. Or are you having problems with the y axis, too?
    Whne you say problems you mean repeatability or tearing belts. Belt only tearing on X axis. It only happened with those long rapid moves seen in video. Maybe the other axis just as bad only didn't tear because their motions are not that long on rapid?

    Be honest with you, all of them are giving me problems. Like I originally said, I had to make new servo adapters to go from the old SEM DC servos to the new rectangular AC servos. I should have made the bolt holes for the bolts holding the plate to "box" ( I don't know what they call those things where pulley and belts go in) rectangular so I could adjust belt tension. I tried rotating
    2-torn-belt.jpg
    basically it is the pulley attached to X axis servo , with a flat screw driver. It took more than just my wrist to do it. Took more like my arm. Not a lot of force, but took some force. Will get a 1/4" torque wrench to that and the other axis' to see how much it takes. Then will remove belts, and try rotating things with torque wrench ( don't know how will do the quill) and see if the belt tension was excessive. If so will try to see about slightly longer belt of same manufacture. Joe Pie from advanced innovations told me might be the belts and I will seriously pursue that.
    Last edited by madmachinst; 07-21-2021 at 05:13 PM.

  17. #17
    Join Date
    Aug 2019
    Country
    UNITED STATES
    State/Province
    Texas
    Posts
    146
    Post Thanks / Like
    Likes (Given)
    17
    Likes (Received)
    19

    Default

    I have one of the old Boss Bridgeports. Even though it's old, I cannot detect any backlash with the ball screws. Once the weighs are lubed, moving the bed is effortless. If you have different distances with equal turns, then it has to be a backlash error...due to broken ball screws or defective parts. Have you checked to make sure you do have ball screws?

  18. #18
    Join Date
    Jan 2007
    Location
    Central FL
    Posts
    906
    Post Thanks / Like
    Likes (Given)
    8
    Likes (Received)
    22

    Default

    Thats what the pictures show. I got a quote to regrind all my ballscrews $1750. I just don't know how to remove the Z axis.

  19. #19
    Join Date
    Mar 2006
    Location
    Vershire, Vermont
    Posts
    2,760
    Post Thanks / Like
    Likes (Given)
    1929
    Likes (Received)
    919

    Default

    Quote Originally Posted by madmachinst View Post
    Whne you say problems you mean repeatability or tearing belts. Belt only tearing on X axis. It only happened with those long rapid moves seen in video. Maybe the other axis just as bad only didn't tear because their motions are not that long on rapid?

    Be honest with you, all of them are giving me problems....
    Yes, I meant that a torn belt resulted in repeatability problems. Tensioning a timing/cog belt properly is quite an exercise, esp if you take the mfgers recommendations seriously.

    Seems to me if all axes are having a repeatability problem, and there's only one torn belt, it's less likely that belts are the problem. Did you change belts?

    Has the oil metering problem been addressed?

  20. #20
    Join Date
    Jan 2007
    Location
    Central FL
    Posts
    906
    Post Thanks / Like
    Likes (Given)
    8
    Likes (Received)
    22

    Default

    Quote Originally Posted by neilho View Post
    Yes, I meant that a torn belt resulted in repeatability problems. Tensioning a timing/cog belt properly is quite an exercise, esp if you take the mfgers recommendations seriously.

    Seems to me if all axes are having a repeatability problem, and there's only one torn belt, it's less likely that belts are the problem. Did you change belts?

    Has the oil metering problem been addressed?
    Haven't addressed oil metering problem cause I don' have the time to tear it apart. All the belts have different tension since I have had to make adapter plates to mount the new servos. Y has known .003" backlash, But I am not dealing with backlash yet. I just want a repeatable steps per inch. Mathematically should be 10,000 steps per rotation on servo times 5 rotations per inch leadscrew times ratio 2:1 on pulleys = 100,000 steps per inch in system. using app on machine I get numbers more like 99,894 on Z 100,090 on X and those are just averages. Different points on screw giving different numbers with variations as much as 250 steps at different locations.

    BTW, it is just the edge of the belt that is torn off, say about 1/16 of inch on about 1" wide belt. have no way to measure stretch on belt cause manual says with 7lb pull should be about 1/4" deflection. Fine can measure Z and Y but X once I take cover off, servo and pulley are removed and no way to measure belt. Servo and pulley permanently attached to the cover.


Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •