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Thread: Cutting shape out of tube stock

  1. #1
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    Cutting shape out of tube stock

    I'm trying to figure out how to cut a shaped hole in brass tubing like this:

    il_fullxfull.1259446821_dq9a.jpg

    I'm guessing I can just dremel it - but the dremel will only be able to do so much. Also, I'll probably use slightly thicker tubing.

    Thanks!

  2. #2
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    One other thing - this example may have been made with flat sheet that would then have been rolled. However, I've seen others online that use spent bullet casings, so I'm guessing there is a way to work with tube stock.

  3. #3
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    What tools do you have? A CNC machine would be nice.
    What's the size of this?
    I've cut curved and straight lines in mild and stainless steel with the plasma cutter, making a tip guide of the shape.
    You can cut sheet brass and aluminum with a carbide-tipped Forstner bit, but best clamped between two pieces of wood. I think I could cut a large diameter hole in a brass tube by turning a wood rod to fit snugly inside then using a shaped piece of wood on the outside. Not hand held! Once the circle hole is cut the straight sides would be easier, saw, milling machine, etc.

    I once cut a bunch of curves on steel propane tank using a fine-toothed blade in a saber saw.

    But I agree, making it from flat stock then rolling and soldering/brazing might be simpler.

    JKJ

  4. #4
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    Size - small. 1/2" diameter MAX, hobby-sized brass tube.

    If I went with flat stock, I could certainly CNC the shape out - but would have to figure out how to roll it (dapping set? I've seen some that will do cylinders on Amazon).

    I'm not opposed to "soldering up" a tube, it will just make interlocking pieces a bit more tricky. I was already planning on (low-temp) soldering bottom and top caps.

    I'm wondering if there is a simple hand-powered way to do this (ie, supposedly soldiers made these sorts of things - what would they have had access to? A machine shop?). I'm thinking a dremel with a cutoff wheel will be too sloppy, although I would be able to chuck it in a vice using a wooden dowel like you suggest.

  5. #5
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    It depends how many you want to make. If it is just one, hold it horizontally on a stick and file across finishing one end with a square edge file and the other end with a round file. If you are making a lot of them, do all the cut outs at intervals on the length of tube before you cut each piece to length. Maths is your friend here. Soldiers did them by hand. Cheers

  6. #6
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    Quote Originally Posted by John Pariseau View Post
    Size - small. 1/2" diameter MAX, hobby-sized brass tube.
    Yikes, so tiny! From the picture I was imagining it 2" or so in diameter. I'd have to think more about that.

    I've made things from round and square hobby store brass tubing, all sized so one slides perfectly into the next size up. Solders easily. The times I've cut slots with round ends I drilled a hole first then cut the slot, but it was always on flat stock. I'd hate to try rolling such small stock by hand! Although that's the way tubing in brass insturments was made according to a How It's Made segment I saw years ago! (but without any slots!)

    I wonder if it could be done on the milling machine, maybe plunge with an end mill for the hole then cut the slot, perhaps switching to a smaller end mill. (Rather than mill off the end of a short piece, maybe just make a long slot with rounded ends and,cut in half to make two at once!) This would make angles on the sides unless the tube was rotated before each cut. Or the head angled a few degrees. Or just clean up by hand.

    I've never seen one of these but from the picture it looks like the outer shell rotates to close. It might be possible to slide the small tube inside first, lock them together with a bit of solder on one end, then mill them together. The two tubes would tend to stiffen each other. If I can find the time I might try this - I keep a box of tubing stock. I don't think it would be this week though, unless a miracle occurs!

    Is there a specific name for these things?

    JKJ

  7. #7
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    OK, a miracle happened. I didn't have 1/2" but I had a piece just over 3/8", another that slid inside, and a piece of rod inside of that to keep it from collapsing in the vise. I soldered the two tubes together in one spot and taped the brass rod to the tubes. The 3/8" end mill was too big, but it worked ok for the test. The rod broke loose from the tape and should have been tack soldered too but I didn't break out a torch, just used an electronics soldering iron and rosin core solder.

    brass_slot2.jpg brass_slot1.jpg

    Forgive the terrible cell phone pictures.

    The rod broke loose from the tape, should have been soldered too, but it worked ok sliding with the end mill.

    I think this method would work OK with a better sized end mill and tube and with a little manual cleanup.

    Oops, farrier is here, gotta run

    JKJ

    Quote Originally Posted by John K Jordan View Post
    Yikes, so tiny! From the picture I was imagining it 2" or so in diameter. I'd have to think more about that.

    I've made things from round and square hobby store brass tubing, all sized so one slides perfectly into the next size up. Solders easily. The times I've cut slots with round ends I drilled a hole first then cut the slot, but it was always on flat stock. I'd hate to try rolling such small stock by hand! Although that's the way tubing in brass insturments was made according to a How It's Made segment I saw years ago! (but without any slots!)

    I wonder if it could be done on the milling machine, maybe plunge with an end mill for the hole then cut the slot, perhaps switching to a smaller end mill. (Rather than mill off the end of a short piece, maybe just make a long slot with rounded ends and,cut in half to make two at once!) This would make angles on the sides unless the tube was rotated before each cut. Or the head angled a few degrees. Or just clean up by hand.

    I've never seen one of these but from the picture it looks like the outer shell rotates to close. It might be possible to slide the small tube inside first, lock them together with a bit of solder on one end, then mill them together. The two tubes would tend to stiffen each other. If I can find the time I might try this - I keep a box of tubing stock. I don't think it would be this week though, unless a miracle occurs!

    Is there a specific name for these things?

    JKJ

  8. #8
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    Cool! This gives me some hope. I did an initial test with a small CNC on some flat brass stock (endcaps). Worked like a charm. I'm going to 3D print a jig to hold the tubes in position on the bed, and mill each separately. I'm hoping that the print will index the tubes precisely, using double-sided tape to hold them in position to the PLA. Another option would be to print in slots for zip-ties, but that makes removal difficult.

    I'm a little concerned about how well this will hold, but I'll be watching it closely in the event it breaks free (hand on the e-stop). Will post some pics once I make some real progress, going to try and do my first trial this week. Alternatively I can get access to a milling machine and can run two different bits along the length... but the CNC will make things go quicker if I can get the process down.

    Also... I considered milling them together instead of separately but I'd like to have the inner shell disappear when the two are aligned. Alternatively, I could file away at the inner shell once milled, but... not that I'm against work, but I need to make 5 of these by the end of December.

  9. #9
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    Here's a preview of the final product - I've already made the bases, caps will be hammered on a dapping block:

    Render.png

  10. #10
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    Curious as to what they are for ???

  11. #11
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    Fill tube with cerometal or machinable wax. Hold it down with 5c block or a vee block. then use endmills of several sizes.. you will have to melt the filler out then file the square corners.
    Bil lD.

  12. #12
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    Quote Originally Posted by Ed Aumiller View Post
    Curious as to what they are for ???
    They don't have a name per-se, but could be considered a "pocket shrine" or "french pocket shrine". General google searches should turn up things like:

    https://www.pinterest.com/pin/406309197607944174/
    https://www.pinterest.com/pin/462181980483706830/
    https://www.pinterest.com/pin/566257353142783886/

  13. #13
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    I 3D printed a guide block to hold two tubes, will run them off today and post results. I don't have any wax or cerometal, but like the idea of filling the tubes if this doesn't work out.

  14. #14
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    Quote Originally Posted by John Pariseau View Post
    ... I don't have any wax or cerometal, but like the idea of filling the tubes if this doesn't work out.
    To hold in the vise without distorting is the reason I put the two tubes together with the brass rod inside. If I didn't have the right size solid rod I was going to turn a wooden dowel to fit.

  15. #15
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    It worked! Though... horrible chatter part of the way through the tube:

    Jig:

    IMG_0395_resized.jpg

    "Finished":

    IMG_0399_resized.jpg

    I'm using a tiny CNC mill with a tiny (1/8") bit. I'm tempted to plunge all the way through the material and mill it in one go, but I don't think the machine will be able to safely cut through the metal in one pass. Either the tape won't hold, or the machine won't have the power to cut through the brass. Other than some rough/poor cutting prior to plunging though the tube all the way, I'm really happy with how this turned out. I'm going to switch to a ball nosed mill to see if that makes a difference.

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