Jacobs chuck arbor

Dieseltech · Mar 3, 2017

Have a Jacobs #3A 1/8-5/8 inch range drill chuck, but have not found what size arbor it needs for the R-8 mill. I see arbor sizes listed as JT0 through JT6. Is there a chart that shows which arbor will fit? Thanks in advance

TimV · Mar 3, 2017

Some quick Googling turns up several references to those chucks having either #2 or #3 Jacobs tapers. Probably are other variations as well, but those two seem prevalent. Page below (and several hundred other ones online and elsewhere) gives Jacobs chuck taper dimensions, which should enable you to measure what you have.
common taper dimensions

markiz41 · Mar 4, 2017

I'm almost certain it's 3JT, but look it up on their website to make sure.

RWT · Mar 4, 2017

I would think a Jacobs chuck would have the size stamped into it because mine does.

That said I agree with markiz41 that it is probably a JT3.

Jacobs chuck arbor

Dieseltech

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TimV

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markiz41

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RWT

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