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A rounding over fixture for small parts

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  • A rounding over fixture for small parts

    Making model engines requires frequent rounding over of the ends of linkages, clevises, etc..
    I made this jig to simplify this operation.

    Top view. The part to be rounded pivots on a central pin which can be changed to suit the size of the hole in the part. The two stops are absolute essentials since the cutter (For safety, I use a rotary file rather than an endmill.) has a tendency to grab the work and pull it out of one's hands. The main bar of the stop is repositionable and can be swung into rough location. Setscrews in the end of the main bar then allow the secondary bars to be slid in and out for fine adjustment.



    A view of the underside. The big block is grasped in the milling machine vise. Through the big block is a threaded rod with a hole into which the various pivot pins fit. Tightening the nut on the threaded rod locks the pivot pin into a V-groove in the main block to keep the pivot pin vertical.



    Another view of the bottom showing the pivot pin holding arrangement.



    In use, the fixture is clamped in the mill vise. A rotary file, held in a collet, is lowered into the slot seen in the other pictures. The y-axis is used to advance the work into the spinning file a few thou at a time. After each advance the work is swung back and forth between the stops to remove material.



    If you make one of these, exercise care in its use. Your hands will be close to the spinning collet and rotary file. For extremely small pieces, I solder the part to a larger piece of metal to use as a handle or else use a small hand vise to grip the workpiece.
    Last edited by mklotz; 04-14-2013, 01:32 PM.
    Regards, Marv

    Home Shop Freeware - Tools for People Who Build Things
    http://www.myvirtualnetwork.com/mklotz

    Location: LA, CA, USA

  • #2
    Darn, Marv, I need one of those yesterday! But you can be sure I'll have one tomorrow if needed. Thanks for the great idea!
    Mel
    _____________________________________________

    I would rather have tools that I never use, than not have a tool I need.
    Oregon Coast

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    • #3
      Neat idea Marv. I end up using my 10" rotary table and it's getting heavier each time I lift it! That's a nice idea because those little radius cuts make a project complete to me.
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      • #4
        I sure enjoy looking at a good problem solver,
        Nice solution Marv.

        Have you tried a multi-flute end mill cutter to see how it compares to the rotary file ?

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        • #5
          Originally posted by Ken_Shea
          I sure enjoy looking at a good problem solver,
          Nice solution Marv.

          Have you tried a multi-flute end mill cutter to see how it compares to the rotary file ?
          I have and that's why I use the rotary file. I'm in no rush and the file leaves a nice finish.
          Regards, Marv

          Home Shop Freeware - Tools for People Who Build Things
          http://www.myvirtualnetwork.com/mklotz

          Location: LA, CA, USA

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          • #6
            That is an interesting fixture, and simple enough to make. I need one, having used a bolt or stud in a the vise too long.

            The rotary file is a good safety tip. End mills are scary when fingers are in close proximity. The mill will suck them in, not just neatly clip a piece off.

            The other danger with an end mill is the strong pull they have to raise the part when milling. Unless the part is firmly clamped, it can be pulled out, damaging the work or tool.
            Jim H.

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            • #7
              Use a down cutting end mill.

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              • #8
                Nice little fixture, Marv.

                I had a thought though. Why isn't this a task better suited to a belt or disc sander? I'm looking into building a full-on 3 wheel belt grinder like the knife guys make. I'm thinking a fixture similar to this one use with one of those would sure be sweet. The same could be done for your disc grinder or even your trusty tool grinder.

                Those belt grinders can sure cut fast. I've been watching some videos on YouTube and that's what finally got me off the dime to start putting one together.

                Cheers,

                BW

                PS Here are a couple of those videos:

                http://www.youtube.com/watch?v=BYllaxuzMk0

                http://www.youtube.com/watch?v=jy_guBBaUTU

                That's a KMG grinder from Beaumont Metalworks. Looks pretty straightforward to fabricate.
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