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  1. #1
    Join Date
    Jun 2010
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    Canberra
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    Default Wrong Drawbar Thread on Collet Chuck :(

    So in buying an MT3 ER32 collet chuck for my mill, I managed to miss the fact that the drawbar size was 1/2" 13tpi, not the 12tpi I need for my machine

    Making up a new drawbar would be easy enough, but would make changing between the collet chuck and the drill chuck a real pain, so I'm wondering if I could re-tap the collet chuck to 1/2" 12tpi?

    As to how, not really sure. I did think about drilling and boring out the existing thread, then pressing/loctiting/welding a solid piece in, somehow, then drill and tap. Again, somehow...

  2. #2
    Join Date
    Jul 2016
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    Melbourne
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    35
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    1,522

    Default

    I think if you currently have a Whitworth drawbar, unless you have a massive amount of tooling I would swap all my tools to a UNC or metric one. Morse taper tooling is cheap enough.

  3. #3
    Join Date
    Sep 2012
    Location
    York, North Yorkshire UK
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    Default

    Hi Rusty, Guys,

    You might find that the chuck is hardened. Certainly mine is, I tried to run a countersink in the end to remove a burr on the top, ended up grinding the burr off with a dremal.
    Best Regards:
    Baron J.

  4. #4
    Join Date
    Nov 2009
    Location
    australia
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    57

    Default

    Just make another draw-bar and be done with it, why waste time attempting to do something stupid.

  5. #5
    Join Date
    Dec 2013
    Location
    Melbourne
    Posts
    19

    Default

    I found the same problem when I had the Herless SM1. It came with a whitworth drawbar - I don’t know why other than perhaps to coerce you to continue to buy tooling from the original retailer. At least some if not all of the MT3 tooling from H&F also used whitworth 1/2” 12 tpi. I remember buying a shell mill holder and a slitting saw arbor for the machine and they were also whitworth. Without any considerate thought I did at one point attempt to re-tap a 13tpi holder but with no great -concentric- success.

    If I was you, I’d probably make another drawbar and add it to the collection. There are cheaper and probably better quality chucks that will become available to you then. If you want to attempt to retap your existing holder, I’ve got a Sutton tap set you are welcome to borrow.

  6. #6
    Join Date
    May 2011
    Location
    Murray Bridge S Aust.
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    71
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    5,945

    Default

    I had a chuck that had an odd thread in it, upon closer inspection it had an insert screwed into it. Not saying yours has, but it's a possibility.
    Would it be possible to tap it to 5/8" then screw in a threaded adaptor to your 1/2" 12TPI, or
    you could make a shouldered adaptor, just need to add some/a spacer.
    Kryn
    To grow old is mandatory, growing up is optional.

  7. #7
    Join Date
    Oct 2008
    Location
    Cairns, Q
    Posts
    666

    Default

    Over the years I have accumulated 3MT mill tooling needing 1/2 UNC, 1/2W, M12, M10 and 3/8W. I reckon it's much easier to make new drawbars to suit the tooling rather than try to modify the tooling to suit the original drawbar.

    Frank.

  8. #8
    Join Date
    Aug 2011
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    Melbourne
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    4,779

    Default

    What a PITA. I just had a quick look through eBay. Most er32 x MT3 are either M12 or 1/2" x 12 tpi. I would see if you can bore and re-tap or put in an insert in your offending er collet. However, like others have said, it may well be quite hard.

    It would drive me batty if I had to use more than one drawbar. In fact my current mill has a captive drawbar, so not that easy to remove. The beauty of it being that when removing a chuck, it ejects it when you loosen but still holds it in place so it does not fall on the table.

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  9. #9
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    Jun 2007
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    sydney ( st marys )
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    Default

    Wether a draw bar is captive or not the tooling should not drop out unless the draw bar is totally removed from the tooling and the operator does not restrain the tooling.

  10. #10
    Join Date
    Aug 2011
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    Melbourne
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    Default

    Quote Originally Posted by pipeclay View Post
    Wether a draw bar is captive or not the tooling should not drop out unless the draw bar is totally removed from the tooling and the operator does not restrain the tooling.
    I see. Maybe I didn't explain it properly or maybe what I have on my mill is just the "industry standard" and everyone except me is used to it. My previous mill had a MT4 spindle and when you undid the drawbar, you could completely remove it from the machine AND the tool would still stay tight in the taper, requiring a bash with a hammer to eject it. If you were not on the ball or not concentrating and not be holding the tooling, the tool would eject and fall onto the table.

    With my current machine, it has a NT40 taper. Loosening the drawbar sees the drawbar loosen off from the tool but the tool still stays firm in the taper. Then when you continue to unscrew the drawbar, it eventually ejects the tool from the taper but the tool is left still hanging onto a half dozen threads of the drawbar. so it never falls onto the table.

    Also the drawbar cannot be removed from the machine unless you drift out a roll pin which connects the upper part of the drawbar to the lower part. Even then, the lower part of the drawbar (the part inside the taper) is still retained inside the spindle. It required removal of the spindle to completely remove.

    Having several different drawbars would not be a viable option for me that's for sure.

    Simon
    Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.

  11. #11
    Join Date
    Jun 2010
    Location
    Canberra
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    Default

    For those who said "just make another drawbar" even though I stated in my post that I'd prefer not to, it's not because of stupidity, thanks, it's because my machine's drawbar is held captive with a top nut that, like Simon's, forces the chuck out of the taper when you loosen it, so changing drawbars requires removing that top nut as well. While some might think this extra bit of work as adding some awesome fun to changing tooling, I'm not so keen if I can avoid it.

    With MT5 tooling for my lathe, the ER32 and ER40 chucks I sourced from different vendors both took M20 drawbars, making me think there was some standardisation with drawbar threads. Clearly I was wrong.

    If 13tpi is more common, then the cheapest solution would be to swap the 12tpi arbor on my drill chuck for a 13tpi version, and make a new 13tpi drawbar.

    That said, hunting around the usual places, I haven't found an MT3 to JT6 arbor with a 1/2" 13tpi thread yet... but there's plenty with M12 around (including the tooling I'm considering from Banggood), so I might settle on that.

  12. #12
    Join Date
    Sep 2012
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    York, North Yorkshire UK
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    Default

    Hi Rusty,

    Nowadays I think M12 is far more common than 1/2" inch 13 TPI Whitworth/UNC Ones. However across the pond you probably find the opposite.
    Best Regards:
    Baron J.

  13. #13
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    Jun 2010
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    Canberra
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    Default

    Just an update to this - I really needed to get my mill working with collets, so I put the collet chuck in my 4-jaw and dialled it in, then drilled out the original thread to around 15mm (didn't act like it was hardened). In hindsight, a bit more planning would have seen me tap the new, larger hole, but I just made up a ~15mm bush with an M12 internal thread and pressed it in with a bit of red loctite. To be even more sketchy, I made up a drawbar from M12 threaded rod with a second nut at the top as a lock nut. Got the job done and works well so far - have removed and re-fitted it about half a dozen times now with no sign of the bush pulling out.

    I might make up a proper drawbar out of 1/2" stock at some point, along with the correct features at the top to allow it to work with the retaining cap, meaning I can release the chuck from taper with a wrench rather than smacking the top with a hammer.

  14. #14
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    Sep 2012
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    Default

    Hi RustyArc,

    I very much doubt that you would need to tighten the drawbar enough to pull the insert out, if you did then I think you would have great difficulty in removing the chuck.

    My M12 drawbar key has a four inch "T" bar and a hand tight nip is enough to lock the chuck in the taper. Just of late, simply because my grip isn't as good as it used to be, I've started using a four inch length of 13 mm aluminium tube on the key handle when ejecting the chuck.

    31-07-2019x001.jpg
    The battery is there just to stop the key from rolling over.
    Best Regards:
    Baron J.

  15. #15
    Join Date
    Oct 2004
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    Default

    Quote Originally Posted by BaronJ View Post

    Nowadays I think M12 is far more common than 1/2" inch 13 TPI Whitworth/UNC Ones.
    Have a care - 1/2" Whitworth is 12 TPI.
    So that's three options!

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