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  • #16
    Not getting into the weeds with regards to tube sizing, it could be possible to fixture a tube such that the two pads are.machined first, then said pads are used as datums for the second setup where the full length pad is mowed. You would have to have sufficient wall thickness to account for any loss of material due to tube distortion along its length.

    Be mindful of the standard tube tolerances for straightness and twist. Depending on the specific flavor of tube, they can be rather generous, so you may need to ask your vendor to cherry pick you a real good piece.
    -paul

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    • #17
      If you can't make it perfect, make it adjustable.

      Weld connectors to the rectangular tubing if necessary, then bolt the frame together. Leave the bolt holes (or slots) oversized to be able to tweak (shim) them flat and square, to the limit of your ability to measure. Bolt your rails to the flat and square frame, and plan for another round of tweaking to get the rails straight, level and parallel.
      SE MI, USA

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      • #18
        Originally posted by psomero View Post
        Not getting into the weeds with regards to tube sizing, it could be possible to fixture a tube such that the two pads are.machined first, then said pads are used as datums for the second setup where the full length pad is mowed. You would have to have sufficient wall thickness to account for any loss of material due to tube distortion along its length.

        Be mindful of the standard tube tolerances for straightness and twist. Depending on the specific flavor of tube, they can be rather generous, so you may need to ask your vendor to cherry pick you a real good piece.
        Paul
        I maybe at a bit of a loss here...which may not be saying allot...
        from what I'm understanding in your reply and after doing a search for Parker I'm confused...
        Am I to assume that there are different MFG out there that offer this type of extrusion and 8020 is just another vendor who supplies or Mfg.'s the extrusion?
        So, if I understand you then the other MFG's you offered will hold tighter tolerances and not be afraid to give their tolerances?
        And some of the MFG's offer a low-cost solution to this type of Extrusion?
        I kind of assumed that all the extrusion was MFG by one MFG out there and then the vendors acquired it and it was then offered in real world application...
        So just because so many others use it and its reasonable (Key word here) may not be the best solution if one wants to hold tighter tolerances?
        Thanks
        Paul

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        • #19
          having assembled larger plasma cutting machinery, (20' x 10') I am with some of the fabricate and shim methods suggested above. It was made with 4 x 4 square tubing with linear rail bolted to it and shimmed true. Tolerance is also subject to the accuracy and adjustability of the X and Y carriages. I am a bit hazy as to how you have enough material on square tubing wall thickness other than xxxx wall to achieve what you are seeking to accomplish anyway. The 80/20 stuff is good to work with but gets expensive really quick. Jim

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          • #20
            Originally posted by jmm03 View Post
            having assembled larger plasma cutting machinery, (20' x 10') I am with some of the fabricate and shim methods suggested above. It was made with 4 x 4 square tubing with linear rail bolted to it and shimmed true. Tolerance is also subject to the accuracy and adjustability of the X and Y carriages. I am a bit hazy as to how you have enough material on square tubing wall thickness other than xxxx wall to achieve what you are seeking to accomplish anyway. The 80/20 stuff is good to work with but gets expensive really quick. Jim

            Ain't that the truth
            Paul

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            • #21
              JB Weld is the wrong epoxy to use for something like this. Self leveling epoxies are made for just this purpose.

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              • #22
                Originally posted by Texasbowhunter View Post

                Paul
                I maybe at a bit of a loss here...which may not be saying allot...
                from what I'm understanding in your reply and after doing a search for Parker I'm confused...
                Am I to assume that there are different MFG out there that offer this type of extrusion and 8020 is just another vendor who supplies or Mfg.'s the extrusion?
                So, if I understand you then the other MFG's you offered will hold tighter tolerances and not be afraid to give their tolerances?
                And some of the MFG's offer a low-cost solution to this type of Extrusion?
                I kind of assumed that all the extrusion was MFG by one MFG out there and then the vendors acquired it and it was then offered in real world application...
                So just because so many others use it and its reasonable (Key word here) may not be the best solution if one wants to hold tighter tolerances?
                Thanks
                Paul
                Misumi sells surface milled aluminum extrusions.

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                • #23
                  Originally posted by elf View Post

                  Misumi sells surface milled aluminum extrusions.
                  Thanks
                  I'll email them and get the cost of materials and such
                  Paul

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                  • #24
                    Interesting reading here - in particular mounting methods / joints and that linear rails may not be as straight as you'd hoped.

                    https://my.mech.utah.edu/~bamberg/re...e%20Design.pdf
                    Last edited by jcge; 07-19-2022, 02:01 AM. Reason: spelling

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                    • #25
                      Originally posted by Texasbowhunter View Post

                      Paul
                      I maybe at a bit of a loss here...which may not be saying allot...
                      from what I'm understanding in your reply and after doing a search for Parker I'm confused...
                      Am I to assume that there are different MFG out there that offer this type of extrusion and 8020 is just another vendor who supplies or Mfg.'s the extrusion?
                      So, if I understand you then the other MFG's you offered will hold tighter tolerances and not be afraid to give their tolerances?
                      And some of the MFG's offer a low-cost solution to this type of Extrusion?
                      I kind of assumed that all the extrusion was MFG by one MFG out there and then the vendors acquired it and it was then offered in real world application...
                      So just because so many others use it and its reasonable (Key word here) may not be the best solution if one wants to hold tighter tolerances?
                      Thanks
                      Paul
                      That is correct. 8020 is one of a multitude of manufacturers of aluminum extrusion profile and IMO, an overpriced and poorly performing option in a lot of ways.

                      It is certainly possible to put linear rails on extrusion and get good dimensional results, but it can take some design and assembly tricks to make it work how you need it to.

                      What are you trying to achieve first off? Specifically what is the end use and how precise are you hoping to make it?
                      -paul

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