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Nesting hollow tubing

  1. Mar 13, 2017 #1

    DaveC426913

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    I am currently building a gadget out of brass hobby tubing, like this:
    https://www.onlinemetals.com/mercha...40_w_tmP3ZkAuFQDxpnFe9cWYJVBs8YT8saAt1F8P8HAQ

    I need about 12 sizes that all nest inside each other. Brass tubing does this nicely, but it is not easy to cut to the precision I want. So i'm looking for alternates.

    Is there anywhere I could get something similar in another material? (I know there's copper and aluminum but probably not in so many sizes). What about styrene plastic?
     
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  3. Mar 13, 2017 #2

    Baluncore

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    It might be easier to find a better way of cutting brass than to find an alternative material.

    I have plugs, (some made from sleeving tube), that fit neatly inside the tube I want to cut. Then I hold the internally supported tube in a slow turning lath and cut it with an abrasive disk that rests on the tool post.
     
  4. Mar 13, 2017 #3

    DaveC426913

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    I've made a jig that holds my Dremel with a cutoff wheel. I can nest the tubes inside each other and cut through a bunch at time. But I only get 95% through before it comes off, leaving a burr. Then I've got to grind a 2mm burr off a 1mm tube.
     
  5. Mar 13, 2017 #4
    Try supporting and clamping the tubes on both ends on a common base. There should be less tendency for it to break away before you cut all the way through.
     
  6. Mar 14, 2017 #5

    Baluncore

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    Maybe cut the tubes a couple of mm long with a crooked and rough end. Use a linishing machine to finish one end square. Then use the same technique to square the other end and set the length against a stop.

    Or; insert a round steel bar in the tube. Then use a small tube cutter on the thin walled, internally supported, tube.
     
  7. Mar 14, 2017 #6

    DaveC426913

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    Yeah, I've been working through these things.
    One of the confounding factors is that I've got to make twice as many ring spacers as I do tubes. A ring spacer is a tube 1mm long.
     
  8. Mar 14, 2017 #7

    Nidum

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    Use a brass or aluminium bar with a selection of drilled holes . Put tube through near size hole , cut off against face of block and fine finish against face of block .

    Make tool from tang end of file to clear burrs in bore .
     
  9. Mar 14, 2017 #8

    DaveC426913

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    An interesting idea. Thanks.
     
  10. Mar 14, 2017 #9
    Good idea - even better if you can fill the tube with something, like maybe hardwood or plastic, to keep from crushing it while cutting.

    Brass is soft enough, you might even be able to do something like that with the brass chucked in a drill, like a mini-lathe, and cut it with a razor knife held against it while it spins (wear good safety googles!).
     
  11. Mar 14, 2017 #10

    Baluncore

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    I have no idea what product value or quantity you make. If you cannot justify tooling-up, then consider sub-contracting the machining to an instrument manufacturer.

    Maybe it is time to consider non-conventional cutting techniques. The following possibilities are not restricted to brass.

    1. You might consider something like wire EDM on a small scale. Or consider a spinning shim disk EDM instead of wire. Second hand Ram EDM machines are cheap and could be modified for cutting tube. There would be no cutter force, just the arcing.

    2. Lasers for cutting are getting cheaper from China. Rotate the tube slowly while cutting.

    3. Next consider a water-jet cutter loaded with an abrasive. Again rotate the tube.
     
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