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  • Gearcutting update

    Hi guys,
    Slowly working on the gear cutting projects but not fast enough for me.

    Plan A:-
    The original idea of turning the Victoria horizontal into a gear hobber by using a set of crossed helicals, a jack shaft and the dividing head has reaches a full stop.
    I have the gears and the jack shaft but found that the input gears for the shaft input on the dividing head are missing. In effect it's a plain dividing head.
    Started to look around for a new head but got sidetracked by Plan B:-

    Plan B is to do away with the gears, jack shaft and drive train all together and replace this by an electronic drive.
    What started this was seeing a small machine at the Midlands Model Engineering Exibition at Donington, UK in October. I have contacted the builder of the machine and he's agreed to build a larger version of the electronic box to drive my big Hoffman head driven by a large type 42 stepper motor.
    I can't say a lot more about the driver box as I don't know anymore until late January when he'll have it ready.
    This will be a genuine hobber able to generate geometrically correct gears from a commercial hob.

    Also in the background is plan C:-
    This is something I have been working on for a while and looks at the problem from a different angle. Biggest bugbear of cutting gears in the home shop is the cutters. Single point cutters are in sets of 8 and can work out expensive. Hobs are even more so.
    Homemade cutters are not easy to make and suffer from poor materials. O1 is about the best we can use. Home made hobs are very hard and laborious to make.

    I have come up with a way to work backwards from a single straight sided rack tooth to produce a geometrically correct involute tooth form. This cutter can be free hand ground, or done in a very simple jig, on a normal bench grinder from an old HSS end mill or slot drill. This cutter will be easy to make, of the correct material, require no hardening and will cut all the numbers of teeth in a range with just the one simple VEE shaped cutter.
    Something similar has been done before where three or five cuts have been taken of each tooth space to form a tooth with a series of flats. My method if it works will do away with this and form a commercially acceptable tooth form

    The idea is to build a purpose built machine but there is no reason why it can't be adapted to fit on say a Bridgeport.
    I have one more problem to sort out with the feed and I can start trials. That's all I'm prepared to say at the moment as I may write this up for one of the magazines.

    John S



    [This message has been edited by John Stevenson (edited 12-23-2002).]
    .

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




  • #2
    John

    You gear hobbin' animal!
    Merry Christmas!

    BTW - a company in the US gave up on gear hobbing and with Haas' help generated a better gear milling program (monster gears) in a VMC. They mill them from solid now.

    Comment


    • #3
      Thrud,
      I had thought about this method or deriditives of it. Would work OK on large stuff but not on small stuff.
      Problem on small stuff is the size of cutter need to get into the root versus the face width.
      Imagine a Myford change wheel of about 20DP.
      To get into the root you are looking at a cutter with about 1/32" diameter, so for a face width of 1/2" you need to use this cutter to go 1/2" deep. Not impossible but a very long and slow job.
      With larger gears the problem is eased.
      I do cut special sprockets this way on the CNC but because they have larger radii and are thinner it's not a problem.

      John S.

      PS. Have a nice one to all.
      .

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



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      • #4
        Sounds terriffic, John. Looking forward to seeing more. Here too things are developing with the gear hobbers. (one is defacto hobbing machine, the other is a simple universal mill conversion.) I'll send you some follow-up info on that when I get my act together.
        Happily, my ordered-for-the-purpose hobs arrived in the mail yesterday. Not cheap, but not at all expensive, considering what they do. Man, they gonna make some badass chips...

        Comment


        • #5
          There was an article in a back issue of Model Engineer, somewhere, about doing that sort of thing on a shaper. It seems like a really good way of doing it, if you can get it set up.

          ----------
          Try to make a living, not a killing. -- Utah Phillips
          Don't believe everything you know. -- Bumper sticker
          Everybody is ignorant, only on different subjects. -- Will Rogers
          There are lots of people who mistake their imagination for their memory. - Josh Billings
          Law of Logical Argument - Anything is possible if you don't know what you are talking about.
          Don't own anything you have to feed or paint. - Hood River Blackie

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          • #6
            John

            I am still working on a variant of your Plan A, tailored to the vertical orientation of a mill/drill and using a plain dividing head. The dividing head is rotated 90* about its main axis and mounted to the vertical of an angle plate afixed to the table. The double-universal variable-length jack shaft then connects directly to the shaft of the dividing head's worm. A simple gear bracket riding with the spindle carries idlers and the target-toothed gear to drive the worm shaft in sync with the spindle and the hob.

            As we discussed in an earlier thread, the uniform motion conditions for the jack shaft are violated by the offset from parallel required to account for the lead angle of the hob. The conclusion of that discussion was that the error introducted was too small to worry over.

            While I am interested in seeing how your other 'plans' turn out, I am still working thru the purely mechanical hobbing approach at the 'how-to' level that most home machinists could implement. The description of 'what' may make interesting reading, but the 'how-to' is more likely to get some gears cut.

            I unfortunately face the same crowded backburner problem as more pressing matters force my attention elsewhere. Progress is slow but not entirely zero!

            Best wishes to you and yours this holiday season, and the same to all who are part of this unique community!



            ------------------
            Rich Kuzmack

            Pi = 355/113 . . . to
            <85 parts per billion
            Rich Kuzmack

            Pi = 355/113 . . . to less
            than 85 parts per billion!

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