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18th Sep 2019, 07:20 PM #1Diamond Member
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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...
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18th Sep 2019, 07:25 PM #2Most Valued Member
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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.
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18th Sep 2019, 08:20 PM #3
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.
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18th Sep 2019, 08:45 PM #4Member
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Just make another draw-bar and be done with it, why waste time attempting to do something stupid.
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18th Sep 2019, 08:57 PM #5Novice
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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.
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19th Sep 2019, 12:39 AM #6Most Valued Member
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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.
KrynTo grow old is mandatory, growing up is optional.
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19th Sep 2019, 02:23 AM #7Golden Member
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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.
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19th Sep 2019, 09:44 AM #8Most Valued Member
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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.
SimonGirl, 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.
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19th Sep 2019, 12:43 PM #9Most Valued Member
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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.
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19th Sep 2019, 04:00 PM #10Most Valued Member
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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.
SimonGirl, 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.
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19th Sep 2019, 08:14 PM #11Diamond Member
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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.
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20th Sep 2019, 12:30 AM #12
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.
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9th Oct 2019, 08:45 PM #13Diamond Member
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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.
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10th Oct 2019, 12:12 AM #14
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.
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10th Oct 2019, 08:42 AM #15Mechanical Butcher
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