Will a Barber Colman #3 cut worm gears? - Page 2
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  1. #21
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    Or, the hobber needn't neccesarily be a BC #3. I have a slightly smaller / simpler Koepfer 110. It gets the job done, and I paid a lot less than the sums mentioned above. See also machines from Mikron, another hobber manufacturer.

    Alternative to John's encoder version above, you can go the mechanical route and, like like John also mentioned, run a shaft through a changewheel arrangement to drive a work arbor. Descriptions and pics have been posted here before; do a search.

  2. #22
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    Cory, the number of flutes are optional. John Stevenson got by with four and as best I can tell, Graham cut 12. More teeth, less chip load per tooth, then there are the one tooth, single fly cutter or shaper methods.

    The later not adaptable to worm gears but does demonstrate single tooth gear cutting and neither are hobbing where the workpiece rotates in concert with the hobb with ratios to suit the desired final product. Think of it as the worm having flutes and engaging the worm gear but regulation is necessary because the worm gear is blank to start.

    Now with Johns tapered cutter, the feed..... never mind, get the book.

    Bob

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    Bob,
    The tapered cutter has nothing to do with this process.
    That 'hob' was a tap before it became a hob

    The machine is started up, blank and hob turn in syncronisation and the hob is touched on the blank.
    Dials are zeroed and the feed is applied by the knee travelling vertical.

    X and Y stay locked at all times.

    .

  4. #24
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    Oh shoot John, with all your other sophistication in this set-up, I was sure that just for fun, you'd added Y feed for increasing depth of cut. Would really complicate the math though, what with 3 synchronized feeds. Couldn't find your encoder in the photo, so my fertile imagination went wild. Former life as a tap huh? Way to utilize a worn lead screw!

    Bob

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    10 fingers. In many cases the gear you are making, if you use some thought and care will be 100x better than the mangled old one, even if it not perfect.

    If the wormwheel blank is held on an arbor it can be removed from the setup and returned without losing index.

    Placing the worm into the partially cut wormwheel and holding it tight into the teeth you can check it on a surface plate with a height gauge to ensure your "make do" angle is as correct as it's gonna get (worm meshed with wormwheel should be at 90 degrees) YOu can also measure the center distance between the meshed worm and wormwheel to know when you have hit the correct dia.

    The cutting tool we used simply had the same tooth form as the worm, and its cutting dia was set to the same or just a touch bigger.

    Cast iron wormwheels made like that to run meshed with a steel worm seemed to work well enough to make the customer very very happy to have the use of a machine again that he could not buy parts for


    Bill

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    Everything was made on a lathe as I don't yet own a mill or a rotary table. That alone made some of the operations rather imprecise to say the least.

    The hob was cut from O1 and then hardened by heating with an Oxy torch, quenched in ATF, and tempered in our domestic oven. Some of the significant challenges were:
    - cutting the a coarse "thread" using a hand ground form cutter without excessive chatter or jamming.
    - approximating the thread pitch for a 1.5mod gear with just the standard & metric change gears/quick change box on my Jet 1024.
    - grinding the slots into the hob with a tool-post mounted dremel and two cutoff wheels in the arbor. (Thats right, no back relief, but its only going to be cutting bronze blanks...)
    - accurately grinding some top relief without reducing the height of the teeth.
    - cleaning up the scale and sharpening the teeth with a small diamond stone after hardening the hob.

    The gear blanks were of course easy to machine, right up until I tried to figure out a way to gash them with the required 19 teeth. A mill and dividing head would have helped this operation immensely, but instead my homebrew solution was to chuck the blank in the lathe and hand broach the teeth just deep & wide enough to engage the hob. One area of considerable experimentation was whether to gash along the helix angle, or simply gash straight and let the hob sort it out. In the end I went with straight slots because gashing along the helix required grinding or milling and couldn't be done in the lathe. If you look at the finished gear you can see evidence of these slots on each tooth at the bottom of the picture.

    The final challenge was coming up with a method to hold the gear blank rigidly on the toolpost so it could be free-hobbed. In the end I threaded a piece of drill rod into a thick steel plate, clamped the plate into an AXA tool holder and mounted the blank on the rod with a couple of small shoulder bearings. Challenges during the hobbing process were:
    - getting the hob started into the blank without slippage. On one or two occasions the gashes weren't deep/wide enough and the hob teeth skipped, thus eventually making an 20T worm.
    - raising/lowering the blank to cut uniformly across the full width of the gear. According to the textbooks, I probably should have started with a larger diameter hob (and only cut once on-center), but thats not how things ended up, and making a new hob in O1 was not appealing.

    All told, from start to finish took about 2 months of weekends and occasional evenings. I'm unlikely be going into production at this rate, but it was much cheaper than the $1800 I was quoted by a custom gear shop. The best bit was I unexpected sold one of these babies to another Jet 1024 owner. [img]smile.gif[/img]

    Hope I didn't bore everyone with my tale!
    Graham

  7. #27
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    Default Barber Colman Gear Hobbing #3

    Quote Originally Posted by Cory View Post
    I am interested in cutting bronze worm gears for my antique Porter Cable sanders. I have researched some and heard that the Barber Colman #3 gear hobbing machine will do this.The gears I want to cut are 2" in dia and 5/8 thick with 21 teeth.I think the worm has a 4 start thread but not real sure. I need help in choosing a machine and the best place to have hobbs made. Also how do you figure out the dim. of the gears?I am new to this and not a machinit by trade but very interested in making these gears.Please help me out. Thanks agian,Cory
    My husband passed away recently and he has a Barber Colman Gear Hobbing Machine 3 gear
    6-10, 6-16, 6-20. It is a Single Thread Index Worm. If you are interested please let me know. The machine is in very good condition. My husband made lots of gears on it for various projects. I can send pics if you like.

    Toni Johnson


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