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  1. #1
    Join Date
    Sep 2007
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    Melbourne, Australia
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    Default Old drill bits as lathe cutters?

    Hey guys,
    I've ruined a few good sets of HSS drill bits. Being the type to never throw anything away, I as wondering if I could grind the bigger ones down to a square tip and use it on the lathe. I'm sure this has been done before, but is it ok to do?

    Cheers

  2. #2
    Join Date
    Oct 2004
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    Southern Highlands NSW
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    Default

    If you mean the shank part that goes into a chuck, this isn't hard enough.
    You might be able to harden it.

    I saw a twist drill modified to use in a CNC machine, cutting serrations on the end of shafts. But that was the hard end doing the cutting.

    Jordan

  3. #3
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    Jan 2011
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    Far West Wimmera
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    Default

    It certainly is. They are used for many similar cutters. The shank is not hard. This can be used to advantage. For home made boring bars and the like, round hss can be better as it will fit in drilled holes. Never throw away broken or worn hss.

    Dean

  4. #4
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    Default

    Quote Originally Posted by Oldneweng View Post
    It certainly is. They are used for many similar cutters. The shank is not hard. This can be used to advantage. For home made boring bars and the like, round hss can be better as it will fit in drilled holes. Never throw away broken or worn hss.

    Dean
    Perfect!!
    I knew the shanks are not HSS hard, but yes, I was thinking boring bars or bits that go into homemade holders.
    I will play around with the grinder.

    Cheers.

  5. #5
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    Sep 2012
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    York, North Yorkshire UK
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    Default

    Hi Guys,

    I agree ! Never throw away broken bit of HSS or carbide for that matter. I use 3 mm shank carbide drills and milling cutters for various jobs. These things break if you look at them the wrong way ! But the 3 mm shafts being solid carbide, they make great boring bar bits and grooving tools. A green or diamond wheel is needed to shape them though.

    The drill shanks can be hardened by heating them up until they cease to be magnetic and then dropping them into a tin of old oil.
    Best Regards:
    Baron J.

  6. #6
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    Default

    I can't visualise a re-purposed drill bit being used as a boring bar.
    Anyone got a photo?

    Jordan

  7. #7
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    Quote Originally Posted by nadroj View Post
    I can't visualise a re-purposed drill bit being used as a boring bar.
    Anyone got a photo?

    Jordan
    We were talking about a cutting tip to fit into a boring bar Jordan. Homemade boring bar with a drilled hole for the cutter.

    Dean

  8. #8
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    Default

    Thanks Dean,

    So, the unfluted portion of the drill bit is used?
    But that's not hard, so I'm still confused.

    Jordan

  9. #9
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    Default

    Quote Originally Posted by nadroj View Post
    Thanks Dean,

    So, the unfluted portion of the drill bit is used?
    But that's not hard, so I'm still confused.

    Jordan
    No, The fluted part is ground down.. Like this .

    boringbar.jpg

  10. #10
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    Default

    There is also a small part of the drill shank that is hard and any unusable HSS tool can be used. I have a planer blade about 400mm x 100mm x 12mm. I should have 2 of them, 1 broken. They came from a timber mill. I have cut off a piece and made a lathe tool from it.

    Dean

  11. #11
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    Default

    Quote Originally Posted by oohsam View Post
    No, The fluted part is ground down..
    OK, it's just where the shank joins the flutes.
    I guess it's easy enough to figure out where the "softness" ends, with a file.

    Thanks,
    Jordan

  12. #12
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    Sep 2012
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    Quote Originally Posted by nadroj View Post
    I can't visualise a re-purposed drill bit being used as a boring bar.
    Anyone got a photo?

    Jordan
    No pictures, but I've re-shaped the end of drills as cutters for all sorts of applications, from flycutting to punches for making brass washers. It's tool steel ! Just shape it to do the job in hand.
    Best Regards:
    Baron J.

  13. #13
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    I guess you give it a bit of a heat treatment, to make it hard?
    From what I read, HSS isn't as easy to harden in the home workshop as carbon steel.

    I accidentally used some HSS to make a tool to undo a special nut. I thought I was brazing on some mild steel. When I tried to then turn it in the lathe, I discovered that the stuff had become glass hard.

    Jordan

  14. #14
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    In my case and also as far as I aware all the others, it is the hard sections being used for the cutting surface. The soft section is simply used for clamping purposes, if it works out that way. It does not matter tho. Use it however it seems to work best. The point is, in my opinion to make use of free HSS quickly and easily.

    Dean

  15. #15
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    Quote Originally Posted by nadroj View Post
    I guess you give it a bit of a heat treatment, to make it hard?
    From what I read, HSS isn't as easy to harden in the home workshop as carbon steel.

    I accidentally used some HSS to make a tool to undo a special nut. I thought I was brazing on some mild steel. When I tried to then turn it in the lathe, I discovered that the stuff had become glass hard.

    Jordan
    Hi Jordan,

    With things like drill shanks, silver steel or gauge plate, the trick is to get the part that you want to use as a cutter sufficiently hot enough that a magnet no longer attracts it, then to rapidly quench it. Usually in oil or sometimes water. As you have discovered it becomes glass hard. Often it's too hard and will chip or break easily, so you have to let it down by tempering. Often its just a matter of heating up to a much lower temperature and cooling it down more slowly.

    I've had cheap drills that have been so hard that the cutting edges simply chip off making them useless ! They are also hard to sharpen because you just can't get a good edge. Some carbon steel tools are like that as well.
    Best Regards:
    Baron J.

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