Jacobs 2A taper.

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xy mosian

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Hello all.
I wonder if anyone could help. I have a 1/2" Jacobs chuck number 6A which clearly states the required arbor to be 2A. I assume that is a reference to the taper.
Sadly I cannot find any information on this taper. Research suggests that the recent equivalent might be the JT2S, 'S' is a reference to short. Sadly I cannot find definitive information about the 2A taper and so cannot match the two. If I could then the problem of finding a 2MT/JT2S arbor rears its head, there do not seem to be many, if any, around.
Can anyone shed light on this problem for me please. The chuck was purchased in the mid '70's to give and idea of time scale invoved.
Thanks in advance,
geoff
 

chaoticbob

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It seems that Jacobs made a model 6A-2A chuck and the 'Taper' after the 2A is just to distinguish from the screwed version. There is an (obsolete) listing for a 6A-2A here in which it is stated that the taper is actually JT2.
Rob.
 

xy mosian

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Rob, I cannot imagine where, or indeed jut how you found that. Thank you very much indeed.
The image shows a chuck which is almost exactly like mine. The exception is the word 'Taper', mine uses the word 'arbor'. Clearly a cause for confusion, for a little while I wondered if this was reference to an arbor made by Jacobs. Perhaps therein lies the reaosn for the change.
Thanks again,
geoff
 

Phill05

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Jacob chucks fit on a Morse taper arbour, the short taper that fits in the chuck is a Jarno taper 1,2,3,4,5,6. depending on what size of chuck to fit on.
 

xy mosian

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Hello Phill05, Thank you for joining in.
Personally I have eveything sorted, in my head anyway, for now. Rob's post, above, and this table:- Drill Chuck Stems | R.D. Barrett have brought some understanding to my dilemma.
Now one thing you have cleared up is the JT prefix. I had believed that this indicated a Jacobs Taper. Not so apparently, 'tis a Jarno Taper.
Thanks again,
geoff
 

chaoticbob

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Rob, I cannot imagine where, or indeed jut how you found that.
...
geoff

Just luck! I have a dim memory of seeing this issue before and searched on 'Jacobs 6A-2A chuck' rather than looking for a 2A taper.

Looking at the Wikipedia article on machine tapers it seems that even if your chuck wants JT2S, JT2 would fit fine - it's the same angle and the diameter at the 'thin' end is the same , there would just be ~3mm of taper protruding from the chuck, which wouldn't be a problem I imagine.

As far as I know, the 'JT' prefix does indeed stand for Jacobs Taper, and the author of the Wikipedia article thinks so too:

"The Jacobs Taper (abbreviated JT) is commonly used to secure drill press chucks to an arbor."

If you haven't yet found a source for a suitable arbor ARC Eurotrade do them in both tanged and drawbar versions for a fiver or so. They also use the JT prefix to designate Jacobs tapers.

Jarno tapers are more a spindle tooling sort of thing I think, ie the taper that fits into the machine spindle rather than the chuck, and they are rare in my experience. But I'm not an authority!

Regards, Rob
 

xy mosian

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Hi again Rob.
Life is somewhat strange. At one time 'tinternet could be used to find anything, I find that these days searching finds far too many answers, and I/we are back to relying on either memory or suitable knowledgeable person, generally with a good memory. Well remembered.

My general preference is to look at RDG tools for such things as this arbor. To help support local businesses etc., they are fairly nearby, but in this case they have no drawbar arbors. As this is for a tailstock I believe a drawbar arbor will be a good choice.

ARC Eurotrade will be getting my order.

Thank you again, and for clearing up the JT prefix. I had not come across Jarno Taper in the past, but then I can think of no reason why I would.

Regards, Geoff.
 

xy mosian

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Just to wind things up. The JT2 taper arbor arrived from ARC Eurotrade and fits as it should:-
20210811_121552_cr.png

Now I do have a chuck key to fit, but for any that need to find one the details are:-
The Pin diameter is 7.9 mm. and there are 11 teeth in the bevel gear.

Thanks again all who helped, especially chaoticbob - Rob.
geoff
 

chaoticbob

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Thanks for letting us know how it worked out. I often make internet searches for answers to my own questions and light on forums where the same question has been asked but conflicting answers are given - then it goes silent, and I never know which one (if any of them) actually worked. Always good to draw a line under a thread!
_________________________________________________________________________________________________________

Rob.
 

xy mosian

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Time was, in the 'Old days' a visit to a tool shop would find the answer. Probably the required part too. Things ain't so easy these days.
xy
 
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