Cutting wide keyways on a shaper
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  1. #1
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    Default Cutting wide keyways on a shaper

    Ever shape a wide keyway? This is how it's done.

    YouTube

    Note how the gentleman in the video cuts the center from the wide keyway he layed out in the hub. Then he uses a full width tool to cut to width. Thus he stages the cut limiting the thrust required. This is fully in line with the way I was taught 50 years ago and 7000 miles away. Small world.

    Shapers and slotters have limited thrust. Form tools require thrust out of proportion to the section of the chip because the necessary force for penetration has to be summed with the resistance of the chip section. A keyway tool is a form cutter in effect even though the cutting edge is straight.

    Another point is the top angle. Too shallow and the tool tries to spring away. Too acute and the tool tries to dig in. Different materials and heat treatments require different top angles if you want to be extra fussy but 4 degrees positive is a good starting point. If the tool deflects away from the cut, increase the top angle.

    Be careful with the tool width. The keyway width will be almost exactly the tool width. Good luck if you finish a bit undersized and try to sideshift to remove the last couple thou. The attempt will drive you nuts. Keyway slotting tools are skinny in the Y direction and easily deflect to the side in an unbalanced cut. Both sides of the tool have to be engaged if the keyway sides are to be parallel and straight. A one-sided skim cut will inevetably bellmouth. The best solution for a slightly undersized keyway is a sharp on-size slotting tool. If that's not possible, you're better advised to hand-work the last couple thou. A dress with the belly of a sharp 3 square file will take less time than preparing an on-sized shaper tool.

    This is all lore I gained from my mentors in 1965.

    Personally, I prefer to broach keyways. Broach sets may be expensive but it's a once in a life time buy. Most small shops will have to buy them only once. Doc Mortenson gave me his Imperial set when he retired and he stole it when he was an apprentice. That makes it at least 70 years old. I replaced some lost shims, the 1/4 broach and made some bushings to time double keys, bushings for tapered bores, etc but otherwise it's good for another 70 years of once a month use. Come to think of it, I haven't used it it ten years. I'm 78, the age I should search for a successor.

  2. #2
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    Kind of the same idea as a cold saw. Every other tooth is slightly V shaped and slightly longer than the square tooth to spread out the stress thereby reducing the force needed to cut. I've done lots of broaching, but never with a shaper. I'm spoiled now with wire EDM. I'll still broach if i have the right size bushing, but faster to wire EDM than make a bushing usually. At 65 I'm not far behind.

  3. #3
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    Worked good on long bore in 12" slotter
    Attached Thumbnails Attached Thumbnails p1000395sm.jpg  

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  5. #4
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    Quote Originally Posted by johnoder View Post
    Worked good on long bore in 12" slotter
    Good ol' Pratt & Whintey, I presume. My career shop had a string of six along the west bay aisle. Very slow and not that great on positional accuray but they could do stuff in their work envelope that would be impossible to accomplish on a manual mill. Tapered splines, for example. Blind internal keyways, machining to sharp inside corners both blind and open. I remember machining a dozen stainless cam buckles intended for 6" wide nylon webbing. Eccentric serrations, funny angles, the bead on the handle, etc all from a single set-up.

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  7. #5
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    And the bar I made to do the job

    "dark" diameter is 2"
    Attached Thumbnails Attached Thumbnails p1000390sm.jpg   p1000391.jpg   p1000392.jpg   p1000393sm.jpg  

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  9. #6
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    this is timely post for me I just took a gear to the machine shop to have it broached 3/4 by 2.5" because I was to chicken to try it on my shaper

  10. #7
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    .750/6.5 inches deep 4140 QT
    Bar is bolted in place of the clapper and there is a small clapper built in to the end of the bar
    All cutting is straight down only a spring cut across the bottom
    20191024_070359.jpg20150202_115840.jpg0810111515.jpg
    With these tools I'm able to cut 40mm keyways in 4140 on a 3hp shaper no problem but its expensive!

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  12. #8
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    Hbjj, do you have a spring in your mini clapper to return to cutting position?

    L7

  13. #9
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    Yes a small coil spring above the clapper pivot pin
    But if I were making a new tool I would probably move it under the pin and pull the clapper back instead of pushing

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