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Old 11-15-2017, 07:45 PM   #1
blockmanjohn
 
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Default Jacobs chuck taper.

Hi, I have a Jacobs chuck with a 3MT shank. To use it in my Bridgeport I have to use a 3MT to R8 adapter. The length of this set up is very long and limits the space between the end of the drill bit and the table.

I thought the best solution would be to replace the tapered shank with a straight one and hold it in a collet.

Looking on E-Bay it seems that I need to know which Jacobs taper I have on my chuck.

My questions are, is this a good route to go, how do I determine the Jacobs taper on my chuck and where do I find information on how to make the trade?

Thanks, John.


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Old 11-15-2017, 10:38 PM   #2
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Not expensive to buy a jacobs or keyless chuck with R8.I have a 16mm ,a 13mmmm and i justbought a 10mm on a mt2 for my small lathe


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Old 11-15-2017, 10:38 PM   #3
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How about an r8 to jacobs taper adaptor .
That would maximise the available Z travel

Usually the taper size is stamped on the chuck and or shank .
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Old 11-16-2017, 01:28 AM   #4
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Jacobs chuck removal wedges are cheap. Get a set to match the JT on your chuck. Pop off the MT3 shank and put in the R8.
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Old 11-16-2017, 03:17 AM   #5
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The chuck body should have a marking like "JT-33" or the like. THAT is the taper in that chuck.

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Old 11-16-2017, 11:14 AM   #6
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Thanks for all the help. Great to hear from people who know what they are talking about. John
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Old 11-16-2017, 12:31 PM   #7
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Just arrived in todays post from China.A 13mm quality keyless chuck
and
R8 sleeve to suit for the mill .Total cost less than $50.Far more accurate and rigid for fine drilling on the mill instead of the 16mm jacobs chuck that came with the mill.Will check of the sleeves to see if the chucks are interchangeable
i think it is a b16 taper
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Old 11-16-2017, 01:55 PM   #8
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Plenty of ideas about the correct way to do it above, so won’t add to that advice. But will add the comment the main reason why i wouldn’t use a collet as first suggested.... unless in a pinch. Is that you will likely increase any runout error.

Cheers,
.adrian
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Old 11-16-2017, 07:39 PM   #9
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In an ideal world you would have a chuck with an R8 shank and at least one with a straight shank. The idea with respect to the straight shank is having the ability to swap the chuck with straight shank tooling which sometimes comes in handy. Id go with an R8 shanked Chuck first if that chuck is large enough to handle at least 1/2" drills.

Straight shank swappability is taken to great lengths with TTE, the Tormach Tooling System. At work we haven't gone that route yet but do have a drill chuck on a 1/2" straight shank. While not the same as TTS it often is very handy to have a bunch of tooling all with one shank size.


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