WTB 3/4" or 19MM square broach to cut Delrin plastic
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    Default WTB 3/4" or 19MM square broach to cut Delrin plastic

    Need to cut a small amount of 3/4" or 19MM square holes in 1.5" thick Delrin Plastic.
    New here: Not sure how this works over here. PM me or Email with info.

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    how it works over here is you actually state what you are looking to do, and what tooling and skills you have to do it with, and what level of precision is needed.

    you want to buy a broach? you want advice on the best way to make said hole? do you want to make a tool? what gear do you have to accomplish said task? is a full square needed, or is a "corners only" on an oversized round as would usually be done in metal ok? then we share that info in the thread so we can assist others in the future.

    to do that in delrin you could pretty much just take a piece of cold rolled and sharpen it up and jam it through. a full DuMont stepped broach is unnecessary. if you have a lathe it would be a 30 min. job to make a really nice 8 or 10 step broach yourself.

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    If you're looking for an alternative for your spline drive need, consider hand grinding small corner radii on the upper section of the broach corners to round the corners in the delrin part. Under the percussive loading of mowing sharp corners may crack quickly and if you're going from a 25mm diameter to the square drive the steel shaft doesn't come to a sharp corner anyway.

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    Quote Originally Posted by cyanidekid View Post
    ...if you have a lathe it would be a 30 min. job to make a really nice 8 or 10 step broach yourself...
    How ya gonna make a square broach on a lathe?

    If the OP knows someone who has an ironworker it would be a simple enough job with a 3/4" square punch.
    Depends how much precision is involved...

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    the tool, not the operation.

    its delrin, don't think you need an ironworker to push it through. prob do it with a drill press if you had a 10 step tool.

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    Rotary broaches work good for this sort of thing and if you don't have the holder you can push it with anything that can grab a 1/2" shank.

    Rotary Broach Tools | Polygon Solutions | ISO Certified

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    Quote Originally Posted by Richard Winn View Post
    You can buy a mortising machine for wood that uses the hollow chisel and drill bit shown above for a few hundred bucks. There are also attachments to convert drill presses to use mortising chisels. But many well-equipped wood shops will have one and could make your square holes quickly and possibly for a small charge.

    I have made square holes in soft plastic that already had a round hole by simply pressing the hollow chisel (with no drill bit inside) through the hole. A DuMont broach would not be my tool of choice for delrin.

    I bought a small rotary broach to make 1/8" hex holes in steel. It worked very well. It was several hundred dollars and I suspect one for 3/4" and the broach would be a thousand or so. And I think it might not cut delrin very well.

    Larry

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    Quote Originally Posted by Richard Winn View Post
    That look like a cheap way to do it. The hole does need to be in the center as it spins at 3000 RPMs. Should be able to predrill on lathe and use this in a mill to hold center. Will look at the rotary broach also.
    Thanks for the help.

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    I hope you do some thorough testing on the new parts before you try selling any...

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    Quote Originally Posted by cyanidekid View Post
    ...the tool, not the operation...
    I still don't understand how you'd make something square on a lathe?

    ...its delrin, don't think you need an ironworker to push it through. prob do it with a drill press if you had a 10 step tool...
    Of course you don't need the tonnage. I just suggested an ironworker because it's a ready made setup but it's
    kind of a moot point because I somehow missed the part about 1.5" material thickness. I don't think you'll find a
    punch that will work with material that thick...

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    Quote Originally Posted by LKeithR View Post
    I still don't understand how you'd make something square on a lathe?
    Like this: YouTube

    But for the purposes of the OP, one could start with some 3/4" square stock of WLA steel, chuck it up in the 4-jaw, center it in real nice by the corners, and chip off the corners partway up. Then advance the slide, chip off a bit more corner, rinse and repeat a few more times until the end is round, and you're all set! For broaching plastic, having the cutting tool pointing a little bit towards the headstock should be enough, you probably don't need to do any other relieving at all.

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