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Thread: How to cut a sq. hole in UHMW

  1. #1
    Join Date
    Mar 2001
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    Southern Oregon
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    1,149

    Default How to cut a sq. hole in UHMW

    Maybe this will be of some interest.
    I needed to replace some plastic bushings in my tractor seat. I check to see what the price would be to replace them $10.40 apiece. I bought a 2X24 inch of UHMW for $10.00.
    The bushings would be 1.5 OD with a shoulder of 2inch and the ID would be a square hole of 1 inch.

    Turning the OD and drilling the ID was a snap. Cutting the square hole took some thinking. So this is what I did I clamped the UHMW in the mill vice using two V blocks.

    A morticing bit with out the drill was placed in the mill and used like a borch cutting out the corners. This did not work too well as the UHMW moved under the pressure of the chisel.


    For the second attempt, I left the ID as drilled and cut the bushings apart and made a pot chuck to hold the 1.5 inch end. The pot chuck was split down one side.

    The pot chuck was placed between the V blocks and mill vice was closed putting pressure on the pot chuck, clamping the UHMW in the pot.


    The center of the ID of the UHMW bushing was found with a dial indicator than it was just a matter of moving X and Y directions 20 thousands or so and using the quill to shove the morticing chisel through the UHMW untill I had my 1 inch square hole.

    The bushing with the blue was the orginal, I did leave the shoulder on the new ones some what larger than the orginal ones.
    Don\'t ask me to do a dam thing, I\'m retired.
    http://home.earthlink.net/~kcprecision/

  2. #2
    Join Date
    Mar 2004
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    St. Louis, Missouri
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    56

    Thumbs up

    The corners of the original have a radius,
    why not just use an end mill to cut the hole?
    It looks good all the same.

  3. #3
    Join Date
    Jan 2003
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    On the Oil Coast,USA
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    16,872

    Default

    Mortising chiesel was the first thing I thought of when I saw your post

  4. #4
    Join Date
    Dec 2005
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    4,448

    Default

    I machined some uhmw today, .. I Discovered turning on the flood or the coolmist helps the finish..

    It works better using wood tooling. Perfect carving medium for casting consistient grain structure.

    I got some more to make...

    Ya see the laser crosshairs on my old mill? It allows quick on/off of the vise now.. I may write down the location of the vise, move mill table, then bolt vise down to intersecting lasers. It ain't as perfect as the camera crosshairs John S came up with.. but it ain't bad for a quick bracket for a 41 chevy truck.
    Excuse me, I farted.

  5. #5
    Join Date
    Aug 2006
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    Hesperia, CA
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    Default

    Not wanting to hijack the thread, but what is UHMW? I'm looking for something cheap to figure out workholding and and process for parts I'll be making when that lathe comes home.

    I realize I won't learn a thing about feed and speed for good finishes on the various metals I'll be using this way, but I won't be wrecking a bunch of expensive material either! Holding it right and knowing what I want to do next come first.

    $10 for a 2 x 24 stick? McMaster gets over $40 for that much 6061.

    SP

  6. #6
    Join Date
    Jun 2006
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    Near DC
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    Default

    UHMWPE (Ultra High Molecular Weight Polyethylene) is slippery stuff, and it cuts a bit cheesy. If I'm sorting out a tricky bit and want to do it in something that's easy to machine, I use Delrin.

    Mmmmmmm...Delrin!

  7. #7
    Join Date
    Dec 2005
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    You left out, it is self lubricating, meaning it is excellent for slides and friction prevention in between moving parts..

    Clamping it.. I have put it into a chuck, started turning it have the tool bite in, and it fly across the room. It is pretty hard to hold down.

    Cutting sliders? a real good miter trim saw works wonders. After the first cut you can determine the loss on the blade, then compensate with your fence for length.
    Excuse me, I farted.

  8. #8
    Join Date
    Aug 2006
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    Wow. Slippery huh?

    But ya know, I just went thru the entire McMaster/Carr plastics section and UHMW seems to be the cheapest material there. PVC was close but I already know what junk that is! If I can hold that UHMW still I oughta be able to hold the real deal.

    BTW, Delrin was $60 for 2x24 round. That's more than 6061.

    SP

  9. #9
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    Mar 2001
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    Southern Oregon
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    Clamping it.. I have put it into a chuck, started turning it have the tool bite in, and it fly across the room. It is pretty hard to hold down.

    David you are right I had to walk across the shop to retieve the one made on the second attempt. I did not want the chuck jaws too tight, as it was it was not tight enough.

    why I did not use an end mill? It was becuase I did not have a small end mill that would match the radius and extend all the way through the hole.
    Don\'t ask me to do a dam thing, I\'m retired.
    http://home.earthlink.net/~kcprecision/

  10. #10
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    Default

    Nice work. I like working with plastic, especially acetal. UHMW isn't bad either and I have big slabs/blocks of that.

    What's a borch?
    Free software for calculating bolt circles and similar: Origin now settable to bottom left! All values positive. Click Here

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