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Gear shaping reality

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  • Gear shaping reality

    Well, Atlas #1 is finally making bevel gears for Atlas #2. So I have a little experience to go with the theory that shapers make gears.

    I don't recommend the process particularly.

    The real issue is the downfeed. Everything is pretty much fine except that. You want to lay back on the downfeed. You want to REALLY lay back on the downfeed.

    After you get a large tooth gear with a toothspace cut well down, you may have a cutting length (measured along periphery of the cutter) getting up towards 0.3 inch or even more.

    Two issues come up.

    1) Chatter. Too much downfeed will cause a chattered cut. Too much may be as little as 0.001 ! (Yes, the Atlas is adjusted with the shims to the factory spec per manual on the ram slides)
    REALLY too much might cause worse problems, of course. That "really" too much might be 0.0025 or so at the end of the cuts for that toothspace.

    2) Adjustment. It is hard to set a downfeed of 0.001, at all, let alone with the ram moving. If the downfeed head is reasonably tight, it won't like to move smoothly, Vactra notwithstanding. This causes acute anxiety when finishing a tooth and not wanting to feed much.

    The alternative of setting downfeed and restarting each time makes a very long process even longer. If you are feeding in almost 0.2 inch total, it is starting to get ridiculous.

    In fact, the real issue is the Atlas is probably too small to cut much below 16DP or so.

    Thats what it looks like from here.

  • #2

    With the Atlas clutch/brake arrangement, why re-set the downfeed with the ram moving? The brake on the Atlas I used to own would stop the ram om a dime, and at slowest speed, I had no trouble with controlling the downfeed. I have never tried to cut gears, however, why do you have to use only one cutter? Seems to me it would be better to rough out the "gap" between the teeth and then use a "finish" cutter to generate the final shape.


    • #3
      That doesn't really help, as you are cutting down the sides. The bottom isn't very wide, and the effective double depth of cut is still going to be long towards the end of the cut.

      Yes, the brake works, that was what I had in mind. Bit going down 0.200 in 0.001 increments is a pain even without working the brake for the last 50 or 80 feed increments.


      • #4
        One might consider cutting one side at a time on such a course pitch. This might require a second bit ground to profile (a challenge in itself, I suspect), so that opposite sides could be ground back for RH & LhH tools, or reversing the blank on the fixture. And how do I line it back up, precisely?

        Just a thought.



        • #5
          Cutting a narrow deep slot seems to risk breaking bits. The one-side approach might be a good one, although the "very coarse" pitch is not so extreme as you think.

          A DP or 12, on a gear a mere 1.4" or so in diameter.

          The best idea seems to be to gash it first with a slitting saw. That tool has little problem with narrow slots.

          In fact, at that point, one might best follow up with an involute gear cutter on the same setup................but wait, that isn't using the shaper............

          The shaper would work very well at DP finer than say 14 or 16. And on spur gears, more than mitre gears, which seem to have relatively lower DPs.


          • #6
            I once modified a "Parting off blade" to work in my Atlas to cut some narrow grooves. Take it slow and easy with the "slotter" and then finish with the form tool bit.


            • #7
              Might work, the slot is only 0.040 at bottom, with finish allowance, and needs to be nearly 0.2 deep.

              I was thinking of using a triangle shaped cutter to rough out most of the stock. Something like an acme thread formed cutter would take out most of it, but if I go very slow, it works as-is. I don't know how much faster it would really be to do it in two steps.

              The slot bit would have the advantage of only cutting on the bottom, but a triangular roughing cutter would let a lot of the depth be cut before the sides hit when using the finish cutter.

              I get about two teeth done per evening, what with other things to do around the homestead, so its happening. I gotta get that machine put together before I am too busy outside to get into things inside!


              • #8
                I meant to ask the other day, what material are you using for the gears and which gears are you having to make?


                • #9
                  The gears are the ram adjust gears. They are zamac, or were, since the teeth of one dropped out the bottom when the machine was moved! That gear now has a smile like a barfighter.

                  I figured to replace them in steel, so I have something approximating a leaded screw machine stock that is being used. I don't have the analysis on the stock, its just laying around here.

                  Brass might have been better, and the option of "checkbook machining" is there too, but being onry, I figured I'd give it a shot.