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Thread: How do you mill an arch/curve

  1. #1
    Join Date
    Aug 2002
    Posts
    7,907

    Post How do you mill an arch/curve

    How do you mill an arch or curve without a rotary table can it be done? I would like to mill a couple of curved slots,to make a slanting saw fence which can be tilted and this needs two curved end pieces at the ends into which the fence can be sloped.
    Please excuse my typing as I have a form of parkinsons disease

  2. #2
    Join Date
    Dec 2004
    Posts
    656

    Post

    i've been thinking of this for a while...

    what's come to my mind (i think i've seen it once) is make some sort of assembly with a big arm and a pivot. have one end be the handle and then have the part clamped down on the other side. drill two holes where the endpoints of the slot'll be, then make really light cuts (like .025") and feed the arm through the arc by hand. i wonder if that'd work at all...
    -paul

  3. #3
    Join Date
    Apr 2001
    Location
    Maine
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    6,714

    Post

    If you can have a pivot hole, you can set up a pivot pin on the milling machine table with a nut to hold the piece down, and swing the workpiece AGAINST THE CUTTER ROTATION by hand. Be doggone sure you don't do anything remotely resembling climb milling though, or the workpiece will climb right out of -- or through -- your hand and cause general havoc. I'm not sure I would try this stunt in a closed slot.

    For a closed slot, set up the pivot pin etc. but drill closely-spaced holes along the curved slot, then clean out the webs in between the holes with plunge cuts with a center-cutting end mill. Then clean up further, if necessary, with further plunge cuts, CLAMPING THE WORK DOWN IN ALL CASES. When the curve is pretty smooth, touch it up with a file to take off the last humps.
    ----------
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  4. #4
    Swarf&Sparks Guest

    Post

    Surely with a lathe, you can knock up some kind of rotary table jig to do the job?
    I know it's another "make something to make something" job, but these jigs have a way of finding other uses
    Rgds, Lin

  5. #5
    Join Date
    Dec 2002
    Posts
    786

    Post

    If you need a radius, it can be cut with a boring head.
    Michael

  6. #6
    Join Date
    May 2003
    Location
    52N 122W Western Kanuckistan
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    Post

    "How do you mill an arch or curve without a rotary table can it be done?"

    Certainly. CNC.
    Free software for calculating bolt circles and similar: Origin now settable to bottom left! All values positive. Click Here

  7. #7
    Join Date
    Feb 2004
    Posts
    1,017

    Post

    What !!!!!!!

    Are you trying to say you haven't bought a rotary table yet. Take that chastity belt off your sporan and buy one.

    They come in handy for cutting curves.

    Allan

  8. #8
    Join Date
    May 2002
    Location
    Beaumont, TX
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    7,251

    Post

    If you don't mind the time it takes, any curve can be milled via an X-Y step approach. Kinda a poor man's CNC.

    Use Excel or some other spreadsheet to make up a table of values and then increment from one to the next with X-Y movements that are only one or two thousanths. It takes a while and for a slot, you need to use a smaller cutter and do the two sides separately, always moving away from the work with the first axis movement (X or Y) and back to it with the second (Y or X). Use a cutter that has as large of a radius as possible to help smooth out the steps.

    Any curve can be done this way, it is just very tedious.

    Paul A.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

  9. #9
    Join Date
    Mar 2001
    Location
    LA, CA, USA
    Posts
    641

    Post

    Do a little trig to lay out a series of points along the midline of the curved
    slot. Successively align these points under the mill and drill with a drill
    diameter equal to the slot width - or use a center cutting endmill to drill if
    the holes overlap. Use a small file to remove the cusps resulting from the
    succession of holes.

    Regards, Marv

    Home Shop Freeware - Tools for People Who Build Things
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    Regards, Marv

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  10. #10
    Join Date
    Sep 2004
    Posts
    2,979

    Post

    Use mastercam and go to full scale size. Develop ypore slot lay it out onto the metal. Drill holes and use the time honoured cnc manual mill machining teqnique. Just move those dials slowly to follow the contour, use a undersized endmill and hand finish to correct shape. Try clamping both parts togetheer so they are identical. Grind file and have fun.

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