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IndustryArena Forum > MetalWorking Machines > Bridgeport Machines > Bridgeport / Hardinge Mills > Bridgeport 1000 vmc retrofit with y axis surface finish issues
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  1. #1

    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

  2. #2
    Community Moderator Jim Dawson's Avatar
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    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

    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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    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

    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.

  6. #6
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    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
    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.

  8. #8
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    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

    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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    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

    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.

  12. #12
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    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

    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.

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