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Thread: Fellows 6A Help

  1. #21
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    Mud- you are correct on 6A and 7 change gear bores being the same size.

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    Ash Gear has the broach for the tri lobe hole if you have a machine to pull it - Ash Gear & Supply Corporation - Broach Fellows Tri-Lobe .875" Tri-Lobe M2 Material .75" Auto Puller

    I've never measured the shape, does anyone know of the specs being available? It looks like there are tight corners in it.

    6a0b7a5b-521e-4e83-b4ac-c2bcf7063bbc.jpg

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    Quote Originally Posted by Mud View Post
    What is the pitch and pressure angle on these gears?
    I believe 6A and 7 gears are interchangeable.
    There's two sizes of tri-lobe. The small ones are 16 DP 14 1/2; I think the big ones are 12 pitch.

    The 3, 3 shaver, 4, most 7's, the 8's, straight-line generators and iirc (been 16 years since I used one) the 8" shaver use the small ones. Also the 10-2 and 20-4 early mechanical machines and the Z. I've heard of some early 7's with round bores but never seen one. The big ones go on the 36 and bigger ? I've never had a 36 but learned to sort through the piles to not get the big ones.

    One has to be careful saying "6" or "7" ... they made them so long and there were so many variations, easy to get bit. But generally, the 6 is the only one that uses straight bores.

    Fellows used to generate the shape. Broaching would make more sense for them but they apparently liked to shape everything. If you've got a hammer ....

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    I do know they are 16 pitch 14.5

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    Quote Originally Posted by Mud View Post
    Ash Gear has the broach for the tri lobe hole if you have a machine to pull it - Ash Gear & Supply Corporation - Broach Fellows Tri-Lobe .875" Tri-Lobe M2 Material .75" Auto Puller

    I've never measured the shape, does anyone know of the specs being available? It looks like there are tight corners in it.

    6a0b7a5b-521e-4e83-b4ac-c2bcf7063bbc.jpg
    Hi Mud,

    Not sure why ( or more to the point, HOW ), but I recalled this post while working on this exact issue. Getting ready to install some TriLobe bores myself, next week. Going to mill them in, but am considering two other methods of approach at the moment. The second choice is to make my own broach for it and do them in the press. The first choice ( because it's ironically fitting ) is to make a tool and actually use the shaper to install the TriLobe profile. Obviously, we can WEDM the TriLobe easily enough, but there are real jobs in the machine and the mill is completely capable of doing the job.

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    You can always drill the corners before you mill the profile. Lay it out in cad and see how big an endmill will just come tangent to the corner radii. Even if ya drill em a little big, the tri lobe drives the gear anyway.

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    Quote Originally Posted by Dan from Oakland View Post
    You can always drill the corners before you mill the profile. Lay it out in cad and see how big an endmill will just come tangent to the corner radii. Even if ya drill em a little big, the tri lobe drives the gear anyway.
    Yes, Sir. Does not appear to be necessary, though. From my cursory interrogations, it appears that it can be milled completely, without concern. Going to throw a few gears on the shadowgraph tomorrow and verify my measurements in the interest of thoroughness. Already have a CAD model of the TriLobe modeled up for the process.



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