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Thread: How to machine an internal hex?

  1. #1

    Default How to machine an internal hex?

    I need to machine 25 parts, each of which has a 1" (across flats) hex shape cut through it. The stock is CRS (1/4" thick) and I'm using a small CNC mill.
    To clean out the corners, all that I've been able to come up with is drilling a small hole and running a tiny cutter into the holes. Is there a better strategy? Filing is out of the question.

  2. #2
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    Get a small shaper for the odd job. An Atlas doesn't take up much room but could easily do this. Gang the parts together if possible and take a full stroke.

  3. #3
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    Can you put a hole in the corner and run out into the hole, like a flank drive socket ? Or is that what you mean ?

    Any chance you can get the customer to alter the spec to allow a bigger hole and cutter ?
    .

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.




  4. #4
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    Since you're only making 25, I'd just go at it with progressively smaller endmills along with your drill holes and the corners approach probably do the first cut with a 1/4" carbide in two passes and a finish cut, then 1/8" and smaller if your really have to, how sharp do the corners have to be?

    If you need really sharp corners, after the first cuts above you could make a broach out of some 1" hex to cut the final corner edges, since it only needs to do 25 it doesn't have to be the greatest home made broach in the world.

    Paul T.

  5. #5
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    Default Broa\tch it

    Make a broatch and then use your/a light (cheap) arbor press.

  6. #6
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    OT's got the right idea. Drill the hole as large as possible, then broach the corners out.

  7. #7

    Default broach

    I have made hex head screws by drilling a blind hole and broaching .
    With a thru hole - no problem.
    With a dead end hole you have the corner material to get rid of (maybe).

    Randy

  8. #8
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    Inside corners are... A problem. But CNC sure makes it easy for you with the small cutters.

    If you have a tilting 4th axis, you might duplicate a trick I once saw, using a pointed cutter at the right angle to make it fit though, and be a square angle.

  9. #9

    Default 1" hex

    Bill, how small is your mill, and do you have a rotary broach holder? This mill broaching video is probably overkill, but maybe it will give you some ideas.

  10. #10
    Join Date
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    Quote Originally Posted by Jim Shaper
    OT's got the right idea. Drill the hole as large as possible, then broach the corners out.
    Lay this out in CAD and you'll see the material removed will be almost a complete circle of 1" diameter. Somewhere in the 5 to 10 ton force to punch/broach. Not an arbor press job.

    Mill the internal hex with as small an end mill as practical. Then broach the small amount left in the corners. Still will be roughly 2 tons force if milled with a 1/4" end mill.

    An easier and possibly less expensive (if your time is worth anything) approach would be to take the parts to a fab shop and have them punch the 1" hex.

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