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Shop made rotary broach for the Rivett

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  • #31
    Originally posted by mattthemuppet View Post
    thanks Max! In the 2nd version the broach rotated (or was supposed to) in the broach holder, with ~1 1/4in of bore/broach contact and the 1/4in BB at the end. I was using grease on the BB and 20W oil on the side of the broach holder bore - probably too thick for this but it spun easily by hand. I'll use ISO32 next time as that's much thinner.

    I need to check that the broach isn't bottoming out of the bore of the broach holder first, then I'll recut the face of the broach to give it more front relief to see if that makes a difference. No harm in fiddling with it while I'm waiting for the bearings to arrive. Most likely at the weekend as I'm behind in my grading and I have a job to apply to this week
    Wait, are your a teacher??
    Max
    http://joyofprecision.com/

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    • #32
      Originally posted by mars-red View Post
      Wait, are your a teacher??
      visiting assistant professor of biology Hoping to become a tenure-track assistant professor somewhere in the US so we can stay here, fingers crossed!

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      • #33
        Originally posted by mattthemuppet View Post
        visiting assistant professor of biology Hoping to become a tenure-track assistant professor somewhere in the US so we can stay here, fingers crossed!
        Truly a noble profession. Good luck, I hope you find your shot at tenure!
        Max
        http://joyofprecision.com/

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        • #34
          Originally posted by mars-red View Post
          Truly a noble profession. Good luck, I hope you find your shot at tenure!
          thanks! I love my job, just wish it was a little easier to find one

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          • #35
            finally got off my butt to try making a new holder, unfortunately with no more success



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            • #36
              recut the front of the broach to give it more relief, hardened it with the MAP torch, set the holder to 1-2deg off axis and fed it into a piece of alu scrap with a clearance hole



              the broach rotates, but all it does is push the material into the hole in a ring. It won't cut the corners. I tried a clearance drill of te size across the flats and one larger than that, both with a lead in chamfer, with no success.

              there is some degree of flex in the tool and tool post though, I wonder if that is having an affect?

              Either way, this is a wash for me, but I'll just reuse that holder as a live center, recut the 1/2in shank to MT1, grind a nice piece of tool steel into a 60deg point and I'm done

              still, a fun exercise

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              • #37
                I'd try going to a larger drill size yet if you still want to give it a go. Try one almost the same size across the corners and see if the wobble does its thing. This would reduce the load on the broach. If it sorta works here you know something else is up.

                That does look like an awful amount of hang out from the tool post. Max's rotary broach is held in his eccentric tool post and there isn't nearly as much hang out. I think you are right - the tool post is probably flexing.
                www.thecogwheel.net

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                • #38
                  Rare win for the ol' eccentric tool post, lol.

                  Sent from my BLN-L24 using Tapatalk
                  Max
                  http://joyofprecision.com/

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                  • #39
                    I did try a larger drill size, although it wasn't quite as large as the diameter of the broach. I did see a lot of flexing though, I'm pretty sure that's the problem. I don't think making a dedicated QCTP holder would be worth it either, it's a pretty small flexible lathe, nothing like Max' Rivett (?).

                    I'll have to put a tailstock mounted one on my project list, though they look a fair bit more complicated than this.

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                    • #40
                      I think I've mentioned this before, but a repeat doesn't hurt.

                      If all you want to do is a couple broached holes (non-production) all you need is the rotary broach cutter itself.

                      Grind the cutter from an old end mill with the typical 2 degree relief. Be sure to use an end mill with a center hole on the shank end.

                      Setup your part in the lathe chuck or collet with the correct size pilot hole with lead in chamfer.

                      Offset the lathe tailstock so a live center in the tailstock pushing on the cutter makes the one degree angle of cutter with respect to the lathe's axis. Use the tailstock feed wheel to push the broach into the spinning work.

                      You'll have to jury rig a way to extract the broach cutter from the hole with lathe turned off. Sometimes easy, other times the broach cutter is tight in the hole.

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