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  • A form tool for gearcutting

    New thread.

    From reading Brian's post it seems as if he's gone about making a flycutter type form tool because the button method is too over whelming or not understood. Personally I can't see why if someone is able to make a model engine they can't turn two buttons to a specified diameter a specified distance apart.

    Anyway it seems to me that the button method can be bypassed and the relieving also done if you can accurately machine the correct radii onto a form tool as opposed to grinding it on by eye.

    We still need the button specifications though and these can be found In Ivan Laws book on page 115, for a given size we need diameter, distance apart, and infeed written down on a piece of paper, no CAD drawing needed.

    Now you can buy off the shelf tapered end mills in various tapers, J&L sell then in 1, 3, 5, 7,10 and 15 degrees per side in various diameters.

    http://www.mscjlindustrial.co.uk/CGI...TEM=TEM-10030B



    Here's a 10 degree one on a 3/8" shank.



    I keep these in for milling insert pockets for lathe and boring tools, 10 degrees is too much for what we need but it will do as an example.

    We put a piece of gauge plate / tool steel [ soft ] in the vise and using a washer bored / drill to the button diameter the hight is set, note we are working on the tool upside down.



    Now centralise the cutter on the blank and then take a cleanup pass across the end to give front rake. Set the dials or DRO to zero.

    Now move over half the centre distance and feed in the amount of infeed, that's one side of the cutter done.
    Repeat on the other side, literally a 5 minute job.

    That's the cutter done, we now have this.



    Top view.





    This clearly shows side rake and front rake of the radii, because of the 10 degree angle it removed a lot of the tooth form at the lower end which has weakened to form but as it was the only tapered cutter I have in the crib it was pressed into service to prove the concept.

    At this stage [ with a correctly formed cutter ] it needs hardening and tempering and is ready to cut.

    This can be used for fly cutting in a holder in the mill or as a shaper tool in a shaper or slotter. It's exactly the same as the button method but without the step of making buttons etc.

    [EDIT] Instead of holding a blank in the vise there is no reason that you could not do these two operations to a rotary cutter with 4 or 5 pre gashed portions on it doing each arm in turn at one side offset and then repeating on the other side.

    .
    Last edited by John Stevenson; 06-20-2010, 06:22 PM.
    .

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




  • #2
    Well Done in My Opinion

    Sir John

    I believe you did an excellant eplanation of making a form cutter.
    it was a brilliant way of making a gear or spline with limited equipment.
    I learned an economical way of making a form cutter.

    Because of the chance I BBS site it has kindled the Idea of starting a home work shop in my garage. I like to tinker.
    I would like to obtain Ivans Law Book but the price jumped ten fold.

    Cheers
    Leesr

    Comment


    • #3
      [QUote] Instead of holding a blank in the vise there is no reason that you could not do these two operations to a rotary cutter with 4 or 5 pre gashed portions on it doing each arm in turn at one side offset and then repeating on the other side.

      I'd like to see the setup for this. Otherwise 2 thumbs up for this way of cutting a single flycutter with the conical mill.
      Last edited by 914Wilhelm; 06-21-2010, 12:26 AM.

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      • #4
        Wilhelm,
        If I get chance tonight I'll do a dummy setup with a piece of steel but I am busy in the shop.

        It is only a proof of concept in that all the machining and necessary angle can be put on accurately using either the dials or a DRO.

        Takes the uncertainty out of it and it's actually very quick. That whole setup took literally 10 minutes and this included pictures, a rotary cutter will take longer as you have the blank to make.
        .

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



        Comment


        • #5
          Well, Ya done a Hob, a form cutter now a flycutting "Cleaver", what's next?? Hacksaw and file??

          Regards Ian.
          You might not like what I say,but that doesn't mean I'm wrong.

          Comment


          • #6
            Nicely done - again

            A very good exercise in lateral and creative thinking John.

            A 5* "tilt" - as per Ivan Laws book - will not only allow a top/back rake if needed - as well as providing a 5* front clearance but will not materially affect either the cutter or the gear tooth profile. That 5* back rake will make cutting a lot easier - and faster - with a lot less tool wear.

            It would not be difficult to finish the profile with a good die grinder.

            Comment


            • #7
              Brilliant John you've even simplified Ivan Law's method.
              Alan

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              • #8
                One of those forehead slapping "why didn't I think of that" moments.

                Comment


                • #9
                  There is one serious disadvantage with this method is that it's fine for gears for small engines etc but once you get up in the gear size, as in DP and number of teeth the buttons increase in size.

                  Take a 60 tooth 16 DP gear.
                  Ivan states you need 15.07 / DP so 15.07 / 16 = 0.941"
                  So you are looking for a 1" tapered cutter. Well they make them but at a price, however it's often possible to get cutters at auctions very cheap BECAUSE they are not standard / normal.

                  If fact looking in a drawer this morning for something I spotted a No4 morse taper reamer - that will make some big gear cutters

                  Like most things it's not the answer to everything it's just one part of a puzzle.

                  .
                  .

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



                  Comment


                  • #10
                    if I have this correctly figured, the only reason the cutter is tapered is that it allows setting the proper size to equate with the button. it has a side benefit of providing relief, but that might be provided another way by tilting head or workpiece.

                    It would be unlikely for a standard end mill to be the proper size. But in case one was, it seems that there would be no objection to using it, so long as it was set off-tram, or the workpiece was, in order to provide relief.

                    because it is not tapered, it would not cut away so much of the material below the edge.

                    So....

                    When you get to larger sizes, it seems that you might be able to use a boring head to generate the circular form. You 23.9mm would be of a suitable size for that.
                    1601

                    Keep eye on ball.
                    Hashim Khan

                    Comment


                    • #11
                      I have a material question:

                      What kinda cutters and toolbit are you using here?

                      You mention tool steel, but what alloy is that exactly?

                      Is there any way to mill hardened HSS? Maybe with carbide? Cermet?
                      Everyone seems to say its impossable(Read as: Very hard) to harden HSS yourself due to the exact temp requirements, but is there anyone that will do it cheaply for one offs?
                      Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                      • #12
                        Wrong thread...
                        Last edited by dp; 06-21-2010, 12:39 PM.

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                        • #13
                          Originally posted by John Stevenson
                          There is one serious disadvantage with this method is that it's fine for gears for small engines etc but once you get up in the gear size, as in DP and number of teeth the buttons increase in size.

                          Take a 60 tooth 16 DP gear.
                          Ivan states you need 15.07 / DP so 15.07 / 16 = 0.941"
                          So you are looking for a 1" tapered cutter. Well they make them but at a price, however it's often possible to get cutters at auctions very cheap BECAUSE they are not standard / normal.

                          If fact looking in a drawer this morning for something I spotted a No4 morse taper reamer - that will make some big gear cutters

                          Like most things it's not the answer to everything it's just one part of a puzzle.

                          .
                          Hey JS

                          for a fly cutter
                          why not use a radius dresser to obtain the approx radii required for the Involute form, dress the grinding wheel?

                          Cheers
                          Leesr

                          Comment


                          • #14
                            Originally posted by J Tiers
                            ...the only reason the cutter is tapered is that it allows setting the proper size to equate with the button. It has a side benefit of providing relief, but that might be provided another way by tilting head or workpiece.
                            But by doing so, you are not now cutting a circular arc, rather a portion of an ellipse.

                            If you don't have a sufficiently large tapered cutter, it might be possible to set up the blank form tool on a rotary table and "circular-mill" it.

                            Comment


                            • #15
                              pencil grinding or pencil milling

                              we do pencil grinding using small sank type grinding wheels. the profile is dress with a dresser that approximates the involute.
                              the same can be used with small center cutting ball nose, end or profile mill cutter.

                              Cheers
                              Leesr

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