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Converting 3MT Tang Arbor for drawbar

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PeterB09/01/2010 09:19:42
14 forum posts
I have a new (old) Vertical Mill with 3MT quill.  I also have a quality Jacobs drill chuck with 3MT arbor - but its the type with a tang at the end.  I want to convert it to open-end with a 3/8 BSW internal thread for my drawbar. 
 
How can I do this without too much aggravation given the hardness of the steel?  Would it be OK to angle-grind the tang-end off then face-off in the lathe with a carbide tip?  I guess what I'm really asking is: would the arbor likely be hardened right through making cutting, facing, drilling & tapping a non-starter? 
 
Thanks in advance for any advice.
 
Peter
Les Jones 109/01/2010 09:37:39
2292 forum posts
159 photos
Hi Peter,
                 If you are only using the chuck for drilling you should not need a draw bar. Using a chuck for milling is considered bad practice as the body of the chuck is also held onto the  MT3 shank with a taper. Even with a draw bar holding the shank into the spindle the chuck body can become detached from the shank with the lateral forces of milling. I do not think there can be a definite answer to your question. I think some will be case hardened and some hardened through. I would try grinding a small amount off the tang and then see if it can be filed.
Les.
mgj09/01/2010 09:53:48
1017 forum posts
14 photos
Supporting Les.
 
The chances of it being through hardened is remote, but it may well be toughened which is worse almost.
 
To be honest, one has to ask whether its worth doing. The cost of a purpose made one is not great, and very cheap given the awkwardness of holding the job, and possibly knocking the end off a tip.
 
Unlike Les i do like a drawbar-ed chuck in a mill or lathe, just to stop any work from causing it to spin after a grab, or from being shaken about in thin metal.
 
So I'd keep using it for drilling, having ordered the replacement, and then swap the chuck over.
Ian S C09/01/2010 10:19:33
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7468 forum posts
230 photos
If the taper is of similar hardness to a MT shanked drill,you'll be able to machine it with a carbide tip tool,but I don't know that you'll get a tap into it.A friend got a bundle of MT drills cheap but needed parallel shanks,so I turned them for him.Ian S C
Circlip09/01/2010 11:53:05
1723 forum posts
Yep, there's ALWAYS one, I've got one with a through hardened shank on a Jacobs chuck, and yes, some of the older M/T drill shanks are tough but machinable and DON'T need carbides to cut them.
 
  Regards  Ian
Ian S C09/01/2010 12:03:51
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7468 forum posts
230 photos
Once you have a draw bar,how do you stop the chuck comming of the Jacobs taper? You could I suppose fasten it the way portable/reversable drills with screw on chucks do,with a screw from inside the chuck into the end of the taper.Ian S C
mgj09/01/2010 12:32:29
1017 forum posts
14 photos
I must admit, I've always asked that logical and very reasonable question- BUT, I've never had one come off yet, and I have never resorted to loctite etc!
Ian S C10/01/2010 00:08:14
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7468 forum posts
230 photos
meyrick it might if he trys milling with it,under normal conditions the morse taper falls out,but if that is restrained the jacobs taper will let go eventually,tapers arn't meant for side loading.Ian S C
mgj10/01/2010 09:07:02
1017 forum posts
14 photos
Could well be - I have never "milled" with a drill chuck, so that's  outside my experience. I have flat bottomed and counterbored holes, but never "pushed sideways". As we said in that discussion on the subject.
PeterB10/01/2010 09:42:59
14 forum posts
Wow!  I go away for 24 hours and there's a wealth of useful replies.  Thank you one and all.  I should have said the chuck is for a drilling job - PCD holes using my new XY DRO.  I have a Clarkson Autolock chuck for milling. 
 
I looked around for a new chuck arbour and found just the thing on ArcEuroTrade's website.  MT3/JT6/M12-drawbar thread all for £4.50 incl VAT.  At that price it must be Chinese - but I'll get one - and just hope that its been accurately made....(?).  While on the site, I also found screw-in tangs of various sizes so one can convert a draw-bar arbour back to a tang arbour for alternative applications in seconds.  And all at £1 each.  (No connection with the Company, etc_). 
 
Thanks again for the super-quick and constructive help.
 
Peter
Ian S C10/01/2010 10:38:47
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7468 forum posts
230 photos
Hi peter sorry to doubt you,I was thinking that if you needed a draw bar you might be going to use an end mill in it sideways,but looks like you'v found the answers,and at those prices you can't go too far wrong.I see those bits in he Arc Euro Trade Catalogue (got copy with ME V-interesting,not much use here),it is useful in that it shows whats available in UK,and lets me know what you are talking about.Good drilling,Ian S C
JasonB10/01/2010 10:58:32
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25215 forum posts
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While you are ordering get a set of their hardened chuck removal wedges so you don't damage the chuck trying to get it off the old arbour.
 
Jason

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