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Thread: Zero backlash CV joint?

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  1. #1
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    Default Zero backlash CV joint?

    Is there such a thing? I know that universal joints are not constant velocity. I need a small joint that can bend at least 30-40 degrees. I have some approx 1-2" diameter stock that I'd like to machine on the 4th axis CNC, but need the end mill to be angled relative to the rotation axis.

  2. #2
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    Try an automotive swivel impact socket.

    Not the chrome plated ones they sell at Sears, but a true, black oxide, impact socket. They use a ball & paddle joint similar to the old "knife & fork" joint VW used to use (on the Beetle)

    A regular universal joint for 3/8" or 1/3" drive might work, except conventional style "U" joints don't like excessive angularity. It causes too much of a speed variation through it's rotation.
    No good deed goes unpunished.

  3. #3
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    You can make a form of CV joint that may be adequate for this task.

    One shaft has a ball on the end and there is a pin through the ball at right angles to the shaft. The other shaft has a hollow barrel with an inner diameter to accommodate the ball and two slots to take the pins.

    There is a similar type of joint, often with three pins, used on the inner end of the half shafts in many vehicles.

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    Weed eater drive cable.
    Gene

  5. #5
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    How big? A lot of (modern) front wheel drive cars have fairly small CV joints, the (real) Mini has one thats about 2 1/2" in diameter IIRC, and is a 6 balls in a cage CV joint.

    Dave

  6. #6
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    If rotation can all be in one direction, I think I would approach the problem from the standpoint of pre-tensioning an available CV joint rather than from the perspective of trying to find one with zero backlash. I was astounded that I was able to buy the half-shafts, new, with both CV joints attached for my 4WD Silverado pickup for about $89. Because they were new, I didn't have to return my cores, so I kept one or both of them to use as "just in case" stuff someday....they would make a cheap PTO type shaft, or flexible drive from some small to medium engine etc. They are designed to turn quite fast (several times engine RPM) and are amazingly tough. In my case, it turned out that likely neither of the CV joints were bad. I had a bad wheel bearing and replacing the half shafts was a job more easily done while the hubs were apart.

    In any case, a half shaft like this for some smallish front wheel drive car might suffice for your purposes.

    Paul
    Paul Carpenter
    Mapleton, IL

  7. #7
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    Quote Originally Posted by pcarpenter
    They are designed to turn quite fast (several times engine RPM)....
    Don't half-shafts turn at wheel speed? Just sayin'...
    Milton

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  8. #8
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    Why does it need to be zero backlash.

    What about a Bridgeport Quill Master type attachment.

    Phil

    Quote Originally Posted by beanbag
    Is there such a thing? I know that universal joints are not constant velocity. I need a small joint that can bend at least 30-40 degrees. I have some approx 1-2" diameter stock that I'd like to machine on the 4th axis CNC, but need the end mill to be angled relative to the rotation axis.

  9. #9
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    These aren't CV joints, but they have quite a selection of very small sized universal joints if you end up going in that direction instead.

  10. #10
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    Default Spiraling out

    Quote Originally Posted by beanbag
    Is there such a thing? I know that universal joints are not constant velocity. I need a small joint that can bend at least 30-40 degrees. I have some approx 1-2" diameter stock that I'd like to machine on the 4th axis CNC, but need the end mill to be angled relative to the rotation axis.
    My guess is that your 4th axis is a rotary table set vertically (axis horizontal) and that the end mill needs to be tilted left or right.

    My guess too is that axis 1 = X, axis 2 = Y and axis 3 = Z

    I noted this post of yours as well although I can't quite understand the set-up:

    Thanks for all the replies so far.

    I forgot to mention that this joint obviously also needs constant length properties. One end will be clamped in the 3 jaw, and the other clamps and turns the workpiece. The workpiece will be supported by a bearing at the clamp end and a live/dead center at the other.

    It needs to be rigid and zero backlash because the 2" stock might be aluminum, and get cut with a 3/8" end mill.

    The swivel impact joint seems like a good inexpensive idea, but I couldn't find out anything about a "ball and paddle" joint.

    You can make a form of CV joint that may be adequate for this task.
    One shaft has a ball on the end and there is a pin through the ball at right angles to the shaft. The other shaft has a hollow barrel with an inner diameter to accommodate the ball and two slots to take the pins.
    OK, but does it have CV properties? This design has the splines in the socket pivoting relative to a fixed point on the ball, whereas in the animation by small planes, the pivot point is moving back and forth along the ball.

    As for how big this joint has to be, I dunno, as long as it meets the stiffness requirements, and costs preferably less than than 20-30 USD.

    Any more, and I'd rather spend my time tilting the 4th axis back and forth manually.

    The bridgeport quill master is too expensive.

    I have to think a little bit about just how important it is for the joint to be totally CV. I'll be cutting a bunch of helices and overlapping spirals, so it would be nice if they are straight and not wavy.
    Is there any reason why the milling head cannot be tilted - or is it fixed? As a BP has been mentioned, I guess the mill is a BP.

    What is the difference between a helix and a spiral?

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