Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Buy or build a cutting jig

  1. Oct 22, 2014 #1

    DaveC426913

    User Avatar
    Gold Member

    I need to make a lot of precision cuts in brass tubing for a project I'm working on. I'm using a Dremel with a cutoff wheel and a vise. The Dremel is strapped to my workstation via a set of wooden tracks so it can slide to and fro, enabling me to cut the tubing in the vise.

    It's not accurate enough. I need sub-millimeter precision.

    I am considering re-making a jig using metal tracks so it's more rigid, but the effort may be prohibitive, since I'd need ways of securing and releasing it, and that adds complexity.

    My question is: does something similar exist (or something I can adapt)? I'm happy to start with a base and modify it as-needed. I'd Google it, but I'm not even sure what I might call it, except "jig".

    vice.png
     
  2. jcsd
  3. Oct 22, 2014 #2

    phinds

    User Avatar
    Gold Member
    2016 Award

    Dave, if you don't get a good answer here, try the WoodWorkingTalk forum. There are a lot of people there who do metalwork as well and although I quit that forum it utter disgust at their gross over commercialization, there are a lot of helpful folks there. Even the woodworkers might have a good idea for a home-brew jig.
     
  4. Oct 22, 2014 #3

    DaveC426913

    User Avatar
    Gold Member

    Thanks. I had thought of asking you, but I assumed you only worked in wood.
     
  5. Oct 22, 2014 #4

    phinds

    User Avatar
    Gold Member
    2016 Award

    Which IS the case. I wouldn't know how to reliably get the tolerances you're looking for, but again, the folks at WoodWorkingTalk and WoodBarter would likely have good ideas.
     
  6. Oct 22, 2014 #5

    Baluncore

    User Avatar
    Science Advisor

    Fine engraving or machining is often done using a pantograph arrangement. The pattern can easily be ten times larger than the object being machined. I have one pantograph here that is used to engrave the surface of small circular cylinders from much larger patterns. The pattern and the work are mounted at different ends of the same shaft. The cutter is controlled by the follower through the adjustable ratio pantograph. google 'pantograph' for many possibilities.
     
  7. Oct 22, 2014 #6

    berkeman

    User Avatar

    Staff: Mentor

    Is there a reason you are using a Dremmel tool cutoff wheel instead of a traditional plumber's copper pipe cutter?

    cutting-copper.jpg
     
  8. Oct 22, 2014 #7

    phinds

    User Avatar
    Gold Member
    2016 Award

    Perhaps you missed where he said he is looking for sub-millimeter precision. Hard to think you could get that w/ a pipe cutter.
     
  9. Oct 22, 2014 #8

    berkeman

    User Avatar

    Staff: Mentor

    I guess that's true, but you could cut it slightly long and grind it down to spec maybe...
     
  10. Oct 22, 2014 #9

    phinds

    User Avatar
    Gold Member
    2016 Award

    Yeah, but then you need a jig to get the grinding to come out even and the right length. Better to do it all w/ one jig, one cut.
     
  11. Oct 22, 2014 #10

    Baluncore

    User Avatar
    Science Advisor

    If you only need to cut the end square and to the right length then using a lathe will give an accurate square cut. For length I would make a simple collet with an adjustable screw as the rear stop. I would make if from steel with only one slot so the three jaw lathe chuck tightens the collet onto the tube to be cut. Eccentricity of the collet is not important for square cuts. The lathe could then be used to finish the second end, flush with the end of the collet.
     
  12. Oct 22, 2014 #11

    DaveC426913

    User Avatar
    Gold Member

    So ... I'm gettin' a metal lathe now?

    What's that? A solid G-note? Second-hand? oo)
     
  13. Oct 22, 2014 #12

    DaveC426913

    User Avatar
    Gold Member

    Something like these would do. But I doubt they're affordable.

    IMG_0753_zps5726756f.jpg


    post-acramill.jpg
     
  14. Oct 22, 2014 #13

    Baluncore

    User Avatar
    Science Advisor

    What range of diameters and lengths do you require?
     
  15. Oct 22, 2014 #14

    DaveC426913

    User Avatar
    Gold Member

    I am cutting 12" stock hollow brass tubing (from a hobby shop) between 1mm and 10mm in diameter.

    I want to cut lengths between 1mm and 40mm. It is these 1mm lengths (one might call the final product a ring) where I have trouble with my homemade jig. Even a small amount of play gives me lousy raggedy-edged pieces that I have to spend precious time grinding to a flat end.

    I misrepresented the sub-millimeter accuracy. It's not that it needs to be accurate - it just needs to be steady. (i.e. my 1mm rings could be 1.2mm, no big deal, but they need to have a clean, flush, flat cut, not ragged).
     
  16. Oct 22, 2014 #15

    DaveC426913

    User Avatar
    Gold Member

  17. Oct 23, 2014 #16

    Danger

    User Avatar
    Gold Member

    I can't believe that you're still too cheap to buy your wife real jewellery after all of these years.

    You didn't mention which kind of cut-off wheel you use. I don't know if they make a metal one large enough to handle a 10mm tube without having it rotated. I assume that you mean the K7 style that uses a fibreglass disk. If you require a deadly flat end for the tube, bear in mind that those disks diminish in thickness as well as diameter while in use. I would recommend a 3-jaw chuck arrangement for holding the tube, such as you might scavenge from a scrapped 1/2" electric drill. You could also buy such a thing as a separate part from a mechanical repair shop. It shouldn't run more than about $20.
    Hmmm.... come to think of it, you could just clamp the whole drill down on a slab of plywood with pipe straps... then you could rotate the piece if necessary without losing zero... hmmm.....
     
    Last edited: Oct 23, 2014
  18. Oct 23, 2014 #17

    DaveC426913

    User Avatar
    Gold Member

    Ar ar ar.
    I've been using the standard ceramic cutoff wheels.
    With a new wheel, I can juuust get a 10mm cut without needing to rotate. But it's not something I can count on sicne I'm not about to put a new wheel in every time.
    No. What's that?

    No, just flush and not ragged. (I gotta de-burr it, but it is very wasteful of time and material if I have to d it a second time.)

    Diameter is a no-brainer but It had not occurred to me that it would diminish in thickness. I wonder if that is part of my problem! By the time I'm almost finished a single cut through, it often seems like I've already gone off true. I've been attributing that to the bending of the brass as the cut proceeds.

    A simple flat vise works fine. I've got one like this:
    http://www.fine-tools.com/york307791b.jpg [Broken]

    Yes. Got the drill clamped to my worktable. The issue is being able to slide the work through the Dremel (or the Dremel through the work). This is what I need the tracks for. Tightly-controlled movement with virtually no play.
     
    Last edited by a moderator: May 7, 2017
  19. Oct 23, 2014 #18

    phinds

    User Avatar
    Gold Member
    2016 Award

    Have you looked at Incra jigs?
     
  20. Oct 23, 2014 #19

    DaveC426913

    User Avatar
    Gold Member

    Not yet. Thanks.
     
  21. Oct 23, 2014 #20

    Baluncore

    User Avatar
    Science Advisor

    Machining principles suggest that you should avoid sliding the cutting disk across the tube. Instead, rotate the tube. If the tube rests in a 'V' it can held in place and rotated by hand. The position of the tube can be controlled by the flat end of a square bar that also rests in the 'V'. The cutter then has two positions, firstly; clear above the tube and secondly; cutting the first mm into the tube. The tube is then rotated in the 'V' while being held against the square stop until the part between the cutting disk and the stop is separated. The process can then be repeated if needed with the same setting. By having a 10 mm AF square bar as the stop, rings of all sizes will be cut square. Careful control of pressure against the stop at the end of the cut will keep the end of the stock tube square, ready for the next ring.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Buy or build a cutting jig
  1. Building a venturi (Replies: 1)

  2. Building a Quadcopter (Replies: 12)

Loading...