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Possible Error in Dimensions in Solidworks Parts Library?

Discussion in 'Suggestions' started by Troubled1, Apr 1, 2016.

  1. Troubled1

    Troubled1 New
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    I was assembling a system in Solidworks based on a 40x80mm C-Rail and ran into an issue where something is not lining up properly.

    When I mate my wheels so they are tangent to the V portion of the rail, then the mounting holes for the wheel assemblies are not concentric with the wheel hubs.

    In the attached picture, I show the distance between the mounting holes on the V-Slot gantry plate, and the distance between the centers of the corresponding locating features on the wheel assemblies. The distance is also such that even turning the eccentric adapter as far as it will go should not be able to correct for it.
    upload_2016-4-1_15-58-10.png
    Am I doing something wrong here, or might there perhaps be a dimension error in the library parts?

    Thanks!
     
  2. Giarc

    Giarc Master
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    I ran into a similar issue with the c beam using the 99.7mm dimension. I used a 5mm bit to drill the original holes and the fit was too tight. I did not notice until I tried to assemble everything. I redrilled my holes with a 6mm bit and all is well. I then made the spacing slightly larger for the rest of the plates prior to cutting.
     
  3. Rob Stehlik

    Rob Stehlik Journeyman
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    I have a similar actuator here and I can confirm that the 99.7mm hole spacing does indeed work for an 80mm wide extrusion. The wheels fit, and the eccentric adjustment is enough. I took the gantry plate off and measured the hole spacing just to be sure, and got 99.72mm.

    So we know the parts work in reality, now I think the question becomes how best to assemble them in Solidworks? Even though using a tangent mate to line up the wheels with the V-slot seems the most intuitive, I would actually recommend doing it a different way. Mate the Right plane on the gantry plate to the Top plane of the C-beam. This will center the gantry plate along the C-beam. Then mate the wheels to the gantry plate, and mate the Right plane of one of the wheels to the centerline of the V-slot. This can be done with a 10mm distance mate from the top surface.

    I know that's probably as clear as mud, but take a look at the Nema 23 leadscrew Driven Actuator in the assemblies part of the library to see what I mean. Using planes to mate things instead of tangencies is generally more reliable. You will notice that with the gantry plate perfectly centered over the linear rail, both of the wheels seem to intersect the V-slot, but in reality the eccentric adjustment will take care of this.
     
  4. Troubled1

    Troubled1 New
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    Thanks Rob - I'll have a look at the assembly.

    When you assemble, is there enough eccentric motion to detach the wheels from the rail? Intuitively, one would think that the design would be such that the eccentric adapter would have the same range of motion inwards and outwards. In practice, however, I guess you would rarely, if ever, need to move the wheels much farther away than the nominal.

    Thanks again!

    Tal
     
  5. Rob Stehlik

    Rob Stehlik Journeyman
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    Once you loosen the screws the wheels come right off, so the amount eccentric adjustment doesn't really effect whether or not you can remove the wheels from the rail.
     

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