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How'd they'd do it? (Gears)

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  • How'd they'd do it? (Gears)

    Buddy of mine had a geared, splined shaft custom built
    (like a transmission gear train) ... machined, hardened,
    ground to size.. for $200. Its about 16" long, a spline
    on each end with bearing seats, and 4 gears in the middle.
    All one solid piece. But that price tag isn't what surprised
    me.

    The 4 gears are different sizes (vary from 1.5" up to 3" or so),
    and they're spaced about 1/8" apart. My question is, how
    the heck do they cut those? The 'longest' gear is about 3"
    long (1.5" OD) .. the sizes are staggered.

    I can't figure out how you cut, say, the smaller center gear,
    without doing damage to the gear on each side (only 1/8" away!).

    EDM is the only thing that comes to mind -- but I'd expect a
    custom EDM job like that to cost much more.

    -Tony

  • #2
    Originally posted by knucklehead
    Buddy of mine had a geared, splined shaft custom built
    ... machined, hardened, ground to size.. for $200. Its about 16" long, a spline on each end with bearing seats, and 4 gears in the middle. All one solid piece.
    Something is getting lost in the translation. Are you sure it's one solid piece? Why would they machine down a 16" x 3" slug of hardenable steel to make the gears, instead of cutting the gears and then fitting them to the shaft?

    A 16" x 3" slug of steel weighs 32 pounds. A slug of hardenable steel like 1045 runs around $50 through the various metal wholesalers, so the machine shop price will be around twice that.

    But more importantly, you say it's hardened and ground to size -- I got several quotes of around $100 to harden and cylindrical grind the MT3 tailstock on my lathe, so hardening and grinding a shaft with integral splines and gear teeth for $100 seems inconceivable.

    In any event, if you did decide that you were willing to waste a lot of stock and cut the gears integral to the shaft (instead of cutting them separately), you could do it by CNC cutting the individual gear teeth. But then I don't see how you'd grind the gear teeth after hardening.
    Last edited by lazlo; 05-05-2008, 03:05 PM.
    "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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    • #3
      Crazy, no? Gear faces weren't ground, just the bearing seats.
      I'll get a picture tomorrow.

      -Tony

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      • #4
        I have seen involute tooth endmills,dunno who made them,wish I knew.

        The local laser shop can produce some very nice gear blanks out of flat plate in a matter of minutes close enough to size that they only need a quick cleanup pass on a mill or grinder to run.
        I just need one more tool,just one!

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        • #5
          Even if it was cut with an involute type endmill, it would be a real small diameter since the gears are only 1/8 away. The average tooth to tooth width of a gear that size would probably dictate that the cutter would have to be 3/16 to 1/4 diameter at the least, there wouldn't be enough room for the cutter to run off of the part with that kind of spacing. Pardon my gear ignorance, I'm not up on the proper terms. Knucklehead, any way you could get us a picture of the part?
          Jonathan P.

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          • #6
            Wouldn't a Fellows gear shaper do that job?
            Jim

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            • #7
              Originally posted by J Harp
              Wouldn't a Fellows gear shaper do that job?
              My thought too. But the gear shaper would have to have a tailstock or steady of some sort. Otherwise that shaft is gonna flex for sure. The only way I know to cut a double decked gear with that small amount of spacing between the gears.
              Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

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              • #8
                I would strongly suspect that the gears are cut separately and shrink fit on the shaft. The joint would be quite hard to see.
                Paul A.

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

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                • #9
                  No Not Shrink fit

                  Seen MANY Old 3 and 4 speed transmission Countershaft gears that are made like that. All Shaped... Fellows or single tooth shaper... Shaped vertically, so supporting is no problem, can sit in a simple hole with clearance for shaft to stick through..

                  One piece chunk of steel..... with around a .125 gap between different diameter gears for chips to clear....
                  Last edited by Bguns; 05-06-2008, 03:53 AM.

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                  • #10
                    Yes I've seen the same. Used to do a lot of tranny mods on manuals Not exactly sure, but I'd suspected they were forged to shape, then finish machined. Kind of expensive for a one-off though if forging were involved.

                    ken.

                    Edit:
                    Recently noticed that a lot of historically forged or cast parts are coming out as built up assemblies. Several more recent automotive camshafts I've used are tubular steel with forged or CNC'd lobes shrunk or welded/brazed to it.

                    ken.
                    Last edited by kendall; 05-06-2008, 04:13 AM.

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                    • #11
                      Originally posted by Bguns
                      Seen MANY Old 3 and 4 speed transmission Countershaft gears that are made like that. All Shaped... Fellows or single tooth shaper... Shaped vertically, so supporting is no problem, can sit in a simple hole with clearance for shaft to stick through..

                      One piece chunk of steel..... with around a .125 gap between different diameter gears for chips to clear....
                      I have also seen where a shaper can cut gears up to a shoulder, but they were arranged in order of size so the shaper could work from one end. If I am reading him correctly, the center gear is smaller than the two on either side of it so there is only 1/8" clearance on each end of the tooth. It's "Down in the Valleeee, the Valley so low Oo O o o o."

                      I don't see how that could be done in a shaper. Only thing I could see for one piece construction is rough forged and them rolled between gear shaped, hardened rollers for final finish.

                      If ground, you would have to use a very small point and CNC. I doubt that would be practical for a production situation.
                      Paul A.

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

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                      • #12
                        As before, having actually worked on the things,,,

                        The larger gears are located on both Ends.... The gear progression in a transmission does NOT go 1 2 4 3 or such.. There is plenty of room, and in some cases just swapping ends of gear cluster allows Shaper tooling to reach.

                        No Rocket Science, done since Teens in mass production Auto/Tractor etc, Transmissions

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