Mitering with a lathe- Mtbr.com
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  1. #1
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    Mitering with a lathe

    Hi guys long time lurker first time poster.
    So I have previously built one kids bike for. My son. I used a cheap east wood tube notcher and starret constant pitch hole saws. Im now looking to up my game with his next frame and then onto my own. I have a small single phase lathe like a 9 inch and an even smaller one that i keep contemplating turning into a permanent tube mitering machine. Has any one else used a lathe successfully for mitering if so wat was the set up? Ive googled and googled but am yet to see a set up that looks much good.
    Last edited by Peter Jefcoate; 03-28-2019 at 10:02 PM. Reason: Spelling

  2. #2
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    Lots of people have done this, though a lathe that small might be tough to get to work well.

    Basically, you need to replace your tool post with a tube holder. There are lots of ways to do that, of course. Then chuck up your hole saw, set the angle you want, and miter away.

    The most difficult part, IMO (and I've only played around with it, I miter on a big knee mill) is making sure you're mitering on center - you'll need to design your tube blocks sized to put the tube on center, or else shim things up as needed (ie, if you're using Paragon blocks).

    It will certainly work, though if you've had good luck with your tube notcher you might not need to use the lathe.

    -Walt

  3. #3
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    The tube notcher works okay i suppose. I just gave a spare lathe id like to use. I guess if I used vee blocks I should be able to shim it to center and be done..

  4. #4
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    Have a look on google images for “lathe milling attachment”. I almost went that route. There are pretty inexpensive options in eBay. You get your angle adjust from rotating the body on the lathe carriage and most have a height adjustable vise. You could just shim up (in height) a drill press vise and get/make some tube blocks. My first full frame was for my son too, now I’m hooked! Best of luck.

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    I inherited a 6x24 mini lathe with the milling attachment and found it not that great for mitering tubes - too much flex between the end of the tube, the tubing block, the milling attachment, and the cross slide.

    I'd say try to rig up something that lets you clamp the tubing block directly to the cross slide in place of the top slide. You might even want to see if you can clamp directly to the carriage.

    The catch on a 6x24 is that there's not much room to work with to keep the tubing block on center. You can do it with the milling attachment because it's offset to sit in front of the carriage, but that offset turns into flex.

  6. #6
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    Quote Originally Posted by Noah240t View Post
    Have a look on google images for “lathe milling attachment”.
    I’ve attempted this. Like Dr Welby, I’ve found it’s not nearly stifff enough. (At least on a mini lathe)
    I make bikes. www.feldybikes.com

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    If you could mount the tube notcher to the lathe carriage and shim it on center it might not be too bad - you'd be able to set a good tool speed and have a controlled way to feed the tube.

  8. #8
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    So the lathe in question is a vintage grayson ,british made. Think my plan is to make a vee block clamp directly on the carriage. The carriage is tee slotted, so i should be able to rig something easy enough.

  9. #9
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    Something like this would help with rigidity. https://www.votawtool.com/magnetic-v...vise-jaws.html

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  11. #11
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    Quote Originally Posted by Noah240t View Post
    It's a nice bit of kit (I have a set of them) magnets would make them better yet.
    I ncredibly
    M yopic
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    A ssholes

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    The Votaw ones have magnets embedded. Probably why they are more expensive. Wouldn't be hard to recess a couple magnets and epoxy them in.

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    Quote Originally Posted by Peter Jefcoate View Post
    So the lathe in question is a vintage grayson ,british made. Think my plan is to make a vee block clamp directly on the carriage.

    You don't want a V-block for mitering thin walled bicycle tubing. With only 4 points of contact and space around it the tube will chatter and walk. Use tubing blocks

  14. #14
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    Quote Originally Posted by m-gineering View Post
    You don't want a V-block for mitering thin walled bicycle tubing. With only 4 points of contact and space around it the tube will chatter and walk. Use tubing blocks
    I've not done any mitering with a lathe, but I have had reasonable luck on a 2 axis CNC Bridgeport. I turned down aluminum slugs that I slipped into the tubes before clamping them with v-blocks. This allowed me to tighten the vise properly without crushing or distorting the tubing. I had no issues with insufficient clamping force on the tubing when using this technique.

  15. #15
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    Quote Originally Posted by CallumRD1 View Post
    I've not done any mitering with a lathe, but I have had reasonable luck on a 2 axis CNC Bridgeport. I turned down aluminum slugs that I slipped into the tubes before clamping them with v-blocks. This allowed me to tighten the vise properly without crushing or distorting the tubing. I had no issues with insufficient clamping force on the tubing when using this technique.
    Straight gauge tubes?
    I make bikes. www.feldybikes.com

  16. #16
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    Both straight gauge and internally butted, making sure that my plug and v-blocks were on a constant thickness portion of the butt in that situation. I haven't tried this with anything resembling a tube with a tapered OD.

  17. #17
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    Makes sense
    I make bikes. www.feldybikes.com

  18. #18
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    The votaw and bikefabsupply.com ones are similar to what's used on the Anvil mitering fixtures and seem to work fine in my experience. I agree that machinist v-blocks wouldn't work well for mitering thin walled tubes.

  19. #19
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    Is your 6x24 a Craftsman/Atlas 618? I have one and, while it may not be the best machine in the world, it's quite capable if you work within its limitations (which may or may not include mitering; I've never tried myself since I've also got larger machines).

    To improve rigidity -which is something a small machine will always be lacking- I suggest you to avoid holding the hole saw using the chuck and get a MT2 arbor inserted into the spindle instead.

    Quote Originally Posted by Walt View Post
    The most difficult part, IMO (and I've only played around with it, I miter on a big knee mill) is making sure you're mitering on center - you'll need to design your tube blocks sized to put the tube on center, or else shim things up as needed (ie, if you're using Paragon blocks).
    My first thought was to replace the entire tool post with one resembling a V-Block lying sideways and with the center line matching the spindle's. This way, it'll will always keep the tube centered vertically, no matter the diameter. No shimming, nothing too time consuming.

    You use the compound's built-in scale to setup the angle.

    If you put conical washers on the screws, allowing the clamp to tilt, it may even miter uneven tubing.

    (I only drew 2 sides but you could use all four)



    I'd assume the long V clamp would be enough to secure the tubing but if you're unsure, you can always buy one of those square 5C blocks and hold the tube with a collet. They go up to 1-1/16" if I remember correctly.
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  20. #20
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    Hi all. Lon from Nova here. One of the slickest tricks I've ever seen for supporting thinwall tubes that distort and especially SHAPED tubes was to use Bondo. Bondo? that's right BONDO.

    Start by using some mold release on the inside of the tube.

    1) mix up Bondo in a paper cup-enough to occupy the volume required for the miter
    2) push the tube in and let it set at the depth required for the miter.
    3) the the Bondo gels, pull the tube out and knock off the external stuff
    4) you can clean the tube with lacquer thinner to get the rest off.

    Miter the tube at will. Knock the chunk of out with whatever size tube is longer the the tube you mitered.

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