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hard-turning ??

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  • hard-turning ??

    Anyone familiar with turning down already hardened tools/workpieces?

    i've seen it done, didnt sound very pretty..

    I have quite a few english-size endmills
    that i'd like to make use of in my all-metric mill. some of them already fit the metric collets, but quite a few, esp the large ones, miss by a hair.

    is shaving them down a bit possible?
    any tips?

  • #2
    You are talking about HSS tool steel. It should be ground.

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    • #3
      Yeah, you can do it. I'd use neg. rake carbide with a fairly generous nose radius.
      And take TINY cuts. This will probably take forever, but you can also rough it down by hand on a pedistal grinder or belt sander. And if the carbide breaks, just keep cutting...that broken edge just became your new cutting edge....

      Don't be surprised if your chips come off green.....
      b

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      • #4
        Get a couple of inch sized collets, 3/8 and 1/2 will do most smallish work.

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        • #5
          Just barely possible. I'd use a vee shaped carbide tool with a sharp point and hope for the best. Tiny cuts. It may not work at all of course.

          How about some kind of toolpost grinder rig up?

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          • #6
            You can hard turn HSS with CBN inserts - if you can afford them (about $120/each here) and have a very ridgid machine. The CBN inserts produce a really nice surface and faster than grinding.

            If you end up grinding them CBN wheels will cut pretty fast - Ceramic Stones, or SiC will also work. An Aluminum Oxide Norton (H) soft bond/open structure wheel also cuts fairly fast and do run cooler than most wheels (great for sharpening tools).

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            • #7
              I'm with halfnut -- buy a couple of inch-dimension collets in the sizes you need and be done with the problem forevermore.

              Or make a couple of collets in the sizes you need. If you don't use them much, mild steel will stand up well enough. Or get a piece of heat-treat 4140. It's not too terrible to machine, and will be pretty durable.


              [This message has been edited by SGW (edited 05-12-2002).]
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              • #8
                I've been thinking more about this question. I still think this is nonsense trying to cut down an endmill, they are an expendable tool, more will be spent trying to cut one down than what the cutter costs.

                There is another alternative, I'm suprized that Thrud didn't mention it, since he mentioned once that he used one. This is a set of double angle collets, the type used with a spanner wrench. They work good.

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                • #9
                  I have to turn down HSS on a regular basis to get tooling to fit colletts, create reliefs on shanks, Things like this. I do have a tool room grinder, but more often than not I turn the shank.

                  When I turn HSS I use a C-6 grade insert with a "2" (1/32) nose radius, though have used a 1/64 NR with good success. I have a CTAP-R turning tool that uses those TPG 221 or 222 inserts.

                  Run at about 150 to 200 RPMs, light feed. Take about .005 to .010 depth of cut, be ready for two finish cuts at size. This works for most HSS, but for Cobalt.
                  CCBW, MAH

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                  • #10
                    halfnut:
                    I sort of missed the part about metric collets - got too excited thinking about hardturned parts!

                    That is a good suggestion - depending on the spindle taper he has a set of ER double angle collets and holder would cover the whole range. My ER-25's cover 1mm-16mm. If you get one, make sure you get a Ball Bearing closing nut with it - puts it in a whole new class of gripping power.

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                    • #11
                      Thrud,

                      Didn't know they had ball bearing nuts for these, used to putting mill in back gear and bearing down. This would be too easy.

                      I see too many problems with trying to hold the endmill to turn it down, this will be as much of a problem as the actual turning process. I've turned down many a drill bit, and a lot of them past the softened shank, a real PITA.

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                      • #12
                        most of the endmills are longshank so i can hold them in the lathe. i've tried twice now and manage only to shave down my insert and do nothing more than buff the endmill.

                        although nice and shiney, they still don't fit.

                        the postings here have given me the idea to try and make a collet. i'm living/working in europe so getting a proper sized collet = big headache / mailorder / customs / etc.

                        my mill uses a DIN (ER?) type collet. doesn't look too hard to turn, but what about cutting all of the slots? will a bandsaw do it? does it *have* to be hardened?

                        other option is getting another (undersized) metric collet and trying to open it up.
                        cons:
                        1. they're hardened
                        2. how do i hold it in the lathe?

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                        • #13
                          anton
                          Just make a sleeve for a larger endmill holder.
                          Any steel will do.
                          Pop a hole in it for the set screw and you're in business.
                          mite

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                          • #14
                            Hey mite, that's too easy. We have to find ways to complify things, not simplify them.
                            Jim H.

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                            • #15
                              HSM had a (2 part) article by Rudy Kouhoupt titled "Make your own lathe collets" Sept/Oct & Nov/Dec 1996 (Yes I have been a subscriber that long). He was making 3C collets however the principle is the same.
                              Hope this helps,

                              Rob

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