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  • Gear hobber

    Gents,
    Here is a link to a video of a small gear hobber that I built using castings from Gary Martin of Martin Model and Pattern in Portland.
    The machine was designed by Tom Hammond and is a development of the Jacobs/Helix design.

    http://youtu.be/ZpJOEj-kX_o

    In the video the machine is cutting a 20dp 14.5pa gear in aluminum. I have cut gears as big as 90 teeth in aluminum so far.
    Tom has used his machine to cut some very small gears.

    We are currently doing some development work to allow helical gears to be cut, and also a differential mechanism to be able to cut prime numbers.

    Cheers
    Pete

  • #2
    I'm probably wrong here, but I thought that in others hobbing videos I've seen, the gear being hobbed was free wheeling and being turned by the angle on the hob. In your machine, it seems that the work is turned by a series of gears, requiring a set of gears for each new gear being hobbed. Is this so?

    Am I remembering incorrectly?
    VitŮŽria, Brazil

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    • #3
      Pete,
      Very interesting and well done video. I didn't know Martin Model had finalised the design. How did you find their drawings? Any mistakes? I have the CES drawings and castings for this gear hobber.

      Dave,
      What you've seen is called Free Hobbing, These Jacobs type hobbers gear the blank to the cutting hob. After going thru the effort of building one of those Jacob type gear hobbers it's probably the cheapest, fastest, and most accurate way to cut gears in a home shop.

      Pete

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      • #4
        Very Nicely Done!!! You should write up an article for the magazine.

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        • #5
          Nice work.

          How do you set the hob helix angle?

          David. A gear hobber leaves nothing to chance including indexing. The motion of the blank is rotation in precise proportion to the hob and this is set by the indexing gears. The quality of the indexing worm and gear on the work spindle is a particular concern and in older generation hobbing machine may comprizee in the work and geat alone 10% of the cost of the whole machine.

          If the product gear could be reliably "wild indexed" the motion in produces may very well be irregular repending on the vaguries of the cutting action and the condition of the hob. Every gear I've seen wild indexed were first "gashed" with a wheel cutter via single indexing to the hob teeth had indexing to work with.
          Last edited by Forrest Addy; 04-22-2012, 07:07 PM.

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          • #6
            Originally posted by Forrest Addy
            Nice work.

            How do you set the hob helix angle?

            At exactly 3:00 you can see the angle set device. The drive shaft to the gear holding mechanism must be extensible, and it has CV couplings at each end.

            It seems that at some point in building this it becomes capable of making its own parts (gears).

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            • #7
              Pete, very nice work!
              .

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              • #8
                AH. I see it. Also at 3:54. Exxx-cellent. I hereby pronounce it a gear hobber. (bang of the Gavel of Pretentiousness)

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                • #9
                  wow! what a great machine! will it fit in a large flat rate box?

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                  • #10
                    How much are the castings .Does he list them on his web site . Haven`t been their in a long time will have to try to find it. That I would like to build.
                    Every Mans Work Is A Portrait of Him Self
                    http://sites.google.com/site/machinistsite/TWO-BUDDIES
                    http://s178.photobucket.com/user/lan...?sort=3&page=1

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                    • #11
                      Where do the hobs come from?
                      1601

                      Keep eye on ball.
                      Hashim Khan

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                      • #12
                        Lane and I were talking about 'hobbing' today, and here this neat rig shows up -- very cool!

                        Here a link to the order form for the separate parts and the kit from Martin Models - I'm afraid a bit pricy for me tho, at $495... its a pain to be short of money.

                        http://www.martinmodel.com/MMPtools-...01-10-2012.pdf
                        If everything seems to be going well, you have obviously overlooked something........

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                        • #13
                          Ahh, I remember when Tom was working on the patterns at TechShop.

                          From what I remember he got a lot of the hobs off ebay. Also I think one or two from Ash Gear.

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                          • #14
                            I hope this isn't too much of a hijack, but what is the advantage of hobbing vs an involute cutter?

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                            • #15
                              Originally posted by fredf
                              I hope this isn't too much of a hijack, but what is the advantage of hobbing vs an involute cutter?
                              1.) 1 hob for all gears of the same pitch vs a selection of involute cutters.
                              2.) More accurate tooth shape from the hob action than the approximations and compromises made within the range of gears each involute cutter is supposed to cut.
                              3.) just plain neat to see it all work.

                              Very nice work and it seems a quiet, wellbuilt machine. Every bit as impressive as the industrial scale hobber I watched cutting 24 and 30 in OD gears with 4 in face width on a factory tour in Kazahkstan. The hobs for that one were almost 6 in OD as I recall...
                              Design to 0.0001", measure to 1/32", cut with an axe, grind to fit

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