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Flexible Coupler causes axis play?

Discussion in 'General Talk' started by Steve B, Feb 15, 2015.

  1. Steve B

    Steve B Veteran
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    I'm part way through the first of my 2 builds and I am curious about the flexible couplers that are used between the motor and the leadscrew. With very little force, I am able to move my axis about 1mm in each direction, extending and compressing that coupler. My concern is that while cutting, this will not have the necessary holding force when making cuts in rigid material in the direction of the axis.

    Of course, I could just wait until I finish the machine and try it out, but figured there may be some feedback on the issue if anyone else has experienced issues. Should I consider rigid couplers? Or, should I put the flexible coupler behind the motor plate and use a bearing to hold the leadscrew? I wanted the coupler on the inside of the motor plate, to keep the motor mounted as close to the plate as possible. A photo of my configuration is attached.

    2015-02-12 13.01.51.jpg
     
  2. Tweakie

    Tweakie OpenBuilds Team
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    Ideally, the leadscrews should always be supported between bearings and to take high loadings the motor end of the screw usually has an angular contact thrust bearing. As you have discovered, relying on the coupler or the motor's bearings is probably just fine for light loadings (laser, 3D printer, etc.) but not really suitable for router operation.

    Tweakie.
     
    Joe Santarsiero likes this.
  3. Tweakie

    Tweakie OpenBuilds Team
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  4. Steve B

    Steve B Veteran
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    As I was wiring the post, I realized I would need to support both ends. I have started the change and got the Z and X axis done, it's much much better. My Z axis is so short, I am only supporting the motor end. I'll post back later with pics. But, unfortunately work has me away from the workshop for a week.
     
  5. PeteW

    PeteW New
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    My flexible coupler I got yesterday has two grub screws (on the motor side, two on the other end) set at 90 degrees to each other. My motor shaft doesn't have any flats machined onto it. Without anything mechanical connection to the motor or the "output" of the flexible coupler, I cannot get it to run true. The motor shaft on its own runs perfectly straight. When when the grub screws are tightened to the motor shaft they push the shaft away from the coupler slightly, so that the coupler now sits a bit skew on the motor shaft. The motor shaft (NEMA 23 with 6.35mm shaft) and 6.35mm coupler seem a reasonably good fit when simply slid onto each other, but the coupler has only a short section that is milled for the motor shaft side. So some play is inevitable, and exaggerated. And I've not been able to reduce the play.

    I think I'd be able to get a much better motor coupling if the coupler had 4 grub screws per end, rather than just two. (I might try to get the engineering shop to cut two new threads in the coupler opposite the existing grub screws.)

    I have bearings, and I guess it doesn't really matter if the coupler itself is a bit skew on my shaft (after all, that kind of play is what it is supposed to be compensating for), but I wasn't really expecting my coupler to become a primary site of misalignment in the build.
     
  6. Giarc

    Giarc Master
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    I drilled additional holes into my shaft couplers then into the shaft a bit, and did the same to the acme screw side. I tapped these holes with an m4 tap. Now they connect and should not be able to shift or slip. I don't have any play that I can see. I have two on each end of the coupler now.
     
    GrayUK likes this.

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