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Thread: Rotary Broach- quick and dirty

  1. #1
    Join Date
    Sep 2008
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    WI/IL border
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    Default Rotary Broach- quick and dirty

    I've just got the link on PM and think it may be interesting for some of our members. Here is how to make a simple rotary broach when you need one in a pinch: https://www.youtube.com/watch?v=M3Ul-s9_MA0

  2. #2
    Join Date
    May 2002
    Location
    SE Texas
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    12,563

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    Looks like a good trick.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

  3. #3
    Join Date
    Mar 2008
    Location
    Kent, U.K.
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    2,566

    Default

    That's how I do it too. This is a hex I cut into an adapter bush for my bike, in 2016 I think.

    https://www.dropbox.com/s/9gzcmsbgka...obble.mp4?dl=0
    Peter - novice home machinist, modern motorcycle enthusiast.

    Denford Viceroy 280 Synchro (11 x 24)
    Herbert 0V adapted to R8 by 'Sir John'.
    Monarch 10EE 1942

  4. #4
    Join Date
    Jan 2003
    Posts
    4,023

    Default

    There's an easier way than that for work that can be broached in the lathe.

    Look in your junk box for an old end mill with a center hole in the shank end. Grind the broach on the cutting end of the end mill with the appropriate clearances. Offset your tailstock and use a live center to push the broach into the rotating workpiece held in the lathe chuck.

    Neither this method or the one shown by the OP provide a way to pull the broach out of a blind hole.

    Rotary broaching is sexy, for only a couple holes I prefer broaching in the hydraulic press though. I have two Slater heads, but they can be too much trouble to set up for onesy-twosy work, long production runs is where the rotary heads excel.

  5. #5
    Join Date
    May 2006
    Posts
    15,574

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    At first I thought wow what a radical offset,,, till I seen the length of the tool bit, the longer the bit the more offset you need... I like it - I will build one when I need it...

  6. #6
    Join Date
    Sep 2015
    Location
    NW Illinois
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    786

    Default

    I notice the video showed a tool with no back taper. In conventional rotary broaches the tool oscillates about 1* about the centerline of the hole. The broach has a 2* taper per side to eliminate interference. The end of the broach is usually ground concave. The starting hole should be about 5% larger than the across flats dimension of your broach. The hole needs to be countersunk so the corners of the broach are inside countersink.

    If you have a press of sufficient capacity you can push a section cut from an Allen key through a round hole. The hole needs to be oversized and you should have a short counterbore to center the
    Allen key.

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