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grinding/making form tools

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  • grinding/making form tools

    I need to cut some gear shaped "teeth" (but not gears) sections on a disk. About the only way I can do it with my equipment is to make a form tool, to shape and them mount it in an arbor, perpendicular to the axis of the mill (vertical) and cut the "teeth" that way.

    If I leave the tool flat on top it will hammer the part like crazy but if I grind some top relief (it is actually on the side when cutting) so that it cuts better it will change the shape of the tool and the profile of the finished part will be wrong. Grinding the sides at an angle that will give the proper profile with "top" rake applied would be, for me, strictly trial and error IE: a lot of extra work to get it right if I can do it at all.

    It's the same as grinding a threading tool, flat top OK, with relief no longer 60 Deg. Do I leave it flat on top or is there a better way.

    Any solutions?????
    The shortest distance between two points is a circle of infinite diameter.

    Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

    Southwestern Ontario. Canada

  • #2
    Unless it's a large form tool putting top rake on will alter the shape but probably not enough to be able to measure it unless you are a micron fanatic.
    .

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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    • #3
      Grind the top relief first, then the side/front profiles. Doing this with a T&C grinder isn't difficult, but doing it by hand takes a lot of care and is very much of a trial and error operation. The final shaping should be done by hand with stones (like filing the surface) and will be quite tedious. You will need something to serve as a gauge.

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      • #4
        Just an alternative, but depending on how much you have to cut and how large a headache you have/are getting, you can always
        send it out to a WEDM shop and they can wire the correct shape with appropriate relief for less dollars than the headache is worth.

        Granted, I own a machine, but I have made many a form tool this way. It's at least worth a call to a local shop to find out. ( unless you just want to learn to do it )

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        • #5

          Circular form, radial top, 0.060" eccentric or so, proper form & clearances.

          Les H.
          The Impossible Takes Just A Little Bit Longer!

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          • #6
            As you mentioned, a form tool needs to be flat on top to produce an accurate form. The hammering can be dealt with by using as rigid a setup as possible and taking small cuts. You can also make a multi-toothed cutter to lessen the chip load on each tooth. Basically it involves rotating the cutter off center a bit while cutting the form to provide relief, and indexing it from tooth to tooth. It's a common method of making gear cutters for clockmaking.

            Making Multi-Point Gear Cutters

            Tom
            Tom's Techniques

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            • #7
              This is just a one off item, it just has to make 5 cuts and then the job is done, so I want to keep it as simple as possible. Its for my own project so shipping it for EDM is out also. The best solution seems to be go slow and cross the fingers.

              The profile accuracy isn't that important so I may grind a slight relief.
              The shortest distance between two points is a circle of infinite diameter.

              Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

              Southwestern Ontario. Canada

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              • #8
                Rough out the openings before you try to mill it, remove as much material as possible by hacksaw or saber saw, nasty file or what ever you have.

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