Bridgeport 1000 vmc retrofit with y axis surface finish issues


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Thread: Bridgeport 1000 vmc retrofit with y axis surface finish issues

  1. #1

    Default Bridgeport 1000 vmc retrofit with y axis surface finish issues

    I am in the process of finishing up a retrofit of a 1998 bridgeport 1000 vmc. I replaced the stock servos and drivers with dmm servos and drivers. Its controlled by centroid acorn board. Ive got everything working on it and I cannot seem to figure out how to get the surface finish of my aluminum parts to have a smooth finish along the y axis travel. Doing a simple square box profile cut shows slight tool marks along the y axis of the part. I originally thought it was a tuning issue with the servo but I've tuned a made test cuts and no tuning seems to make it better or worse. I dont know if it's a ballscrew issues or the end bearings going out. The table on the machine is pretty heavy and I really can't get any noticeable play in anything. The video below will show an indicator on the end of the y ballscrew as its doing the test cut. Then I show the y axis of the part and then the x axis. The y axis definitely has something going on with it but I need some help determining where to start looking.
    Thanks

    https://youtu.be/dyJ_mmkPF70

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  2. #2
    Community Moderator Jim Dawson's Avatar
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    Default Re: Bridgeport 1000 vmc retrofit with y axis surface finish issues

    It almost looks like the X axis is bouncing a bit. Increasing the feed speed and step over might help. When I want a really nice surface I do a spiral down finish cut to compensate for my somewhat loose X axis.

    Jim Dawson
    Sandy, Oregon, USA


  3. #3

    Default Re: Bridgeport 1000 vmc retrofit with y axis surface finish issues

    I'm completely new to machining. I got the machine for a good deal and could pass it up. So you think the issues is the x axis? The test part im cutting is square and the x axis looks great compared to the y axis finish. Changing feeds and speeds and more engagement doesn't make it any better.



  4. #4
    Community Moderator Jim Dawson's Avatar
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    Default Re: Bridgeport 1000 vmc retrofit with y axis surface finish issues

    The unevenness that you show in the video can really come from a lot of different places. Yes, it could be the Y axis ball screw or thrust bearings. But it could also be loose gibs, X axis ball screw or thrust bearing, or even the spindle bearings. And I say spindle bearings because I had a problem that only showed up on a Y axis move, and it went away when I had my spindle rebuilt.

    Another possibility is servo motor tuning. I can feel some vibration in my Y axis and sometimes I see the same type of pattern. Put your fingers on the table when making a cut, and try to feel what is happening.

    Jim Dawson
    Sandy, Oregon, USA


  5. #5

    Default Re: Bridgeport 1000 vmc retrofit with y axis surface finish issues

    The spindle has already been rebuilt one time on the machine. I think it was back in 2012 or so. I dont have the paperwork with me right now. But... the maxhine had set a few years at different machine shops because it had an electrical issue that no one could figure out. Hopefully its not the spindle. Ive tuned on those servos for hours and hours literally. If the table is vibrating what would that point to? Its hard to do any manual moving of the table or measuring by pushing and pulling on anything because the size of the table and weight just doesn't move easily. I can tighten up the gibs easily and rule that out real quick. I could put the indicator on the end of the x axis ball screw and see if i have any movement. Im just trying to narrow down where to look. I have this machine at my house in my shop. Its only going to be used for making home project type stuff. But.. the surface finish is enough to make you aggravated...at least for me it does.



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    Default Re: Bridgeport 1000 vmc retrofit with y axis surface finish issues

    Quote Originally Posted by Raceman17 View Post
    The spindle has already been rebuilt one time on the machine. I think it was back in 2012 or so. I dont have the paperwork with me right now. But... the maxhine had set a few years at different machine shops because it had an electrical issue that no one could figure out. Hopefully its not the spindle. Ive tuned on those servos for hours and hours literally. If the table is vibrating what would that point to? Its hard to do any manual moving of the table or measuring by pushing and pulling on anything because the size of the table and weight just doesn't move easily. I can tighten up the gibs easily and rule that out real quick. I could put the indicator on the end of the x axis ball screw and see if i have any movement. Im just trying to narrow down where to look. I have this machine at my house in my shop. Its only going to be used for making home project type stuff. But.. the surface finish is enough to make you aggravated...at least for me it does.
    How many flutes is the cutter it looks like it is at every flute contact, the Y axis on these machines have a lot of weight on it so a big portion of this is caused by slipstick, what size servo are you using on this machine

    Mactec54


  7. #7

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    Quote Originally Posted by mactec54 View Post
    How many flutes is the cutter it looks like it is at every flute contact, the Y axis on these machines have a lot of weight on it so a big portion of this is caused by slipstick, what size servo are you using on this machine
    I'm using 3 flute carbide yg1 endmills. The servo on the x and y axis is a 1.3kw dmm servo.



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    Default Re: Bridgeport 1000 vmc retrofit with y axis surface finish issues

    Quote Originally Posted by Raceman17 View Post
    I'm using 3 flute carbide yg1 endmills. The servo on the x and y axis is a 1.3kw dmm servo.
    The servo should be fine try a 5 or 6 flute for a finish pass no more than .005" cut and see if it is still the same slow feed as well

    Mactec54


  9. #9

    Default Re: Bridgeport 1000 vmc retrofit with y axis surface finish issues

    Shouldn't the finish be the same on all axis reguardless of the x or x axis? My x axis is fine. Why would u have to change paramaters just for one axis to come out good?



  10. #10
    Community Moderator Jim Dawson's Avatar
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    Default Re: Bridgeport 1000 vmc retrofit with y axis surface finish issues

    Quote Originally Posted by Raceman17 View Post
    Shouldn't the finish be the same on all axis reguardless of the x or x axis? My x axis is fine. Why would u have to change paramaters just for one axis to come out good?

    It could be mechanical or electrical. Problems like this are a bit hard to track down sometimes. As Mac said, slip/stick can cause this along with a number of other possible causes. If you get the same result loading the tool more, then the problem could be a loose X axis. Feeling the vibration of the table when cutting is one pretty good way to get an idea of what is moving. Your fingers are pretty sensitive to direction of movement, even very small movements.

    Jim Dawson
    Sandy, Oregon, USA


  11. #11

    Default Re: Bridgeport 1000 vmc retrofit with y axis surface finish issues

    Ok. Im on vacation for a few days and not at the shop. I will definitely report back on what ive tried it will be next weekend at the earliest. Thanks all for the suggestions.



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    Default Re: Bridgeport 1000 vmc retrofit with y axis surface finish issues

    Quote Originally Posted by Raceman17 View Post
    Shouldn't the finish be the same on all axis reguardless of the x or x axis? My x axis is fine. Why would u have to change paramaters just for one axis to come out good?
    You may have to in your case, your machine is far from new, and there are many things that can cause this what is the Gain setting you are using

    Mactec54


  13. #13

    Default Re: Bridgeport 1000 vmc retrofit with y axis surface finish issues

    Main and speed are both around 30ish. Integration is set at 5. I was messing with it the other day moving them up to try to make the servo more rigid to see if that was the issue with tuning.



  14. #14

    Default Re: Bridgeport 1000 vmc retrofit with y axis surface finish issues

    Today i tightened the gibs on the machine to the point where the servos would fault out. There still is the wavy surface finish issues on the y axis. Tightening the gibs did not provide any better surface finish. How can I check the end bearings for play? I moved the carriage close to the front of the machine and placed a prybar between the y axis bearing block and the lower portion of the table. I put the indicator with a ball bearing on the end of the y axis ball screw. Prying the table away from the bearing block i may have got between .0003-.0005" of travel on the end of the ball screw. Its really had to tell because the table and screw just slightly moves with the force. You can feel the servo fighting back against the force. If i just run the table back and forwards i get about .0002" sweep on the indicator when it changes directions.



  15. #15
    Community Moderator Jim Dawson's Avatar
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    Default Re: Bridgeport 1000 vmc retrofit with y axis surface finish issues

    Do the same thing, but put the indicator on a non-moving surface and indicate the table. Pry in both directions and look at the readings. Then do the same thing in the X axis.

    Jim Dawson
    Sandy, Oregon, USA


  16. #16

    Default Re: Bridgeport 1000 vmc retrofit with y axis surface finish issues

    Here's a video... i readjusted the gibs then did the test. The indicator is on the y saddle and I'm prying againt the bearing block. The issue im having is that the ball screw is slightly moving when i pry. The servo fights the movement and for the most part goes back to the original position. Do the gibs need to be locked up to check the movement in the ballscrew? At the end of the video the servo faults out because of to much force.

    Here's the video.




  17. #17

    Default Re: Bridgeport 1000 vmc retrofit with y axis surface finish issues

    So today I guess I was bored... i starting looking around and was looking at the lubrication lines. I noticed that the lube feed line where it connects to the machines main distribution block at some time over the past few months of running had a kink right in the line where it went into the manifold. This got me looking closer and I decided that I needed to remove the table off the machine to make sure all the oil passages are clean and the oilers aren't plugged. There are several oilers buried under the table so I pulled the table off and have it sitting on the shop floor. Ive got to clean/replace a few lines and check all the oilers. Several of the passages going to the gibs were full of gunk. I dont think they were completely blocked but they weren't clean either. Now I'm trying to decide if I wanna try to pull the saddle off and see if all the oil passages are clean. I dont have an overhead hoist and my engine hoist won't fit between the machine base to get it over the saddle to pick it up straight. Idk I have to look at it some more to see what i can come up with.

    When I bought the machine it had been sitting for several years probably over 5 years.. so the oil passages may or may not be clean. The machine is oiling though but im not certain its oiling to the correct amount. Ive got the lube layout drawings so I can follow that easy but knowing if the passages in the castings are clean is a different story. I know the table has a few plugs that I'm assuming are used to check to see if oil is flowing to that location. On a side note the plastic liners with the oil grooves cut in them look pretty good. There is some scratches on one end of the table liners where there was some light corrosion on the way.



  18. #18
    Member cncmakers001's Avatar
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    Default Re: Bridgeport 1000 vmc retrofit with y axis surface finish issues

    Quote Originally Posted by Raceman17 View Post
    Here's a video... i readjusted the gibs then did the test. The indicator is on the y saddle and I'm prying againt the bearing block. The issue im having is that the ball screw is slightly moving when i pry. The servo fights the movement and for the most part goes back to the original position. Do the gibs need to be locked up to check the movement in the ballscrew? At the end of the video the servo faults out because of to much force.

    Here's the video.
    So maybe change a bigger torque motor will help.

    http://cncmakers.com/cnc/controllers/CNC_Controller_System/CNC_Retrofit_Package.html


  19. #19
    Community Moderator Jim Dawson's Avatar
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    Default Re: Bridgeport 1000 vmc retrofit with y axis surface finish issues

    You really need to lock the ballscrew when doing this test. It doesn't tell you much if the ballscrew turns.

    Jim Dawson
    Sandy, Oregon, USA


  20. #20

    Default Re: Bridgeport 1000 vmc retrofit with y axis surface finish issues

    I've went over the table lube plumbing lines and cleaned them out and checked all the oilers. There were a few that were not pumping oil. Now that the table is off the machine I can look at the ballscrew on the x axis easily right now. Ive locked the x axis ball screw and put the indicator on the ball nut mount. If I grab the nut and try to move it back and forth with as much hand pressure as I can i get about .0005 or so movement. I dont know whats acceptable or if this is an accurate test. Something else i did was with the x axis ballscrew locked down i am able to grip the ballscrew with a rag and turn as hard as i can with hand pressure. I get about .0002 movement on the ballnut mount. If i just grab the ballscrew and flex it up and down by hand pressure i get about .0005 movement as well. Any suggestions would be appreciated. Here is a video of the movement.




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Bridgeport 1000 vmc retrofit with y axis surface finish issues

Bridgeport 1000 vmc retrofit with y axis surface finish issues

Bridgeport 1000 vmc retrofit with y axis surface finish issues