Thread: Jacobs chuck - arbor question

I want to put into service an old keyed 3-jaw Jacobs drill chuck of standard design. I'd guess, wildly, that it might be 50 years old. I will need an arbor for it. The issue is what Jacobs taper is the right one to fit the back socket of the chuck. An attempt to email Jacobs failed.

This is not a particularly big chuck but was made to a heavy duty standard. The barrel is diamond knurled, not longitudinally ribbed or plain, and the bore easily accepts rod bigger than 1/2 inch but seems to be just a hair shy of accepting a 5/8 rod. The knurled barrel is 2-1/4 inches OD, and the base of the nose 1-11/16 OD. The engraving on the base of the nose says "No. 3", along with "The Jacobs Mfg. Co., Hartford, Conn. USA" and "Jacobs Drill Chuck, Pat. Sept. 16, 1902". It is not clear to me if the "No. 3" is the model number of the chuck or the JT #. I'm hoping one of you can save me the trauma of measuring with the gauge balls. If a photograph is required, we can do that.

It is simple. Scroll down to the Jacobs at the bottom of the page and pick the one nearest the big end of the hole in the chuck.

Standard Tapers

McMaster-Carr also has a good section on this in their online catalog.

Thanks guys. John, I did pretty much as you suggested. What came closest was a JT3, but I have an arbor with a JT3 taper and it does not fit at all - a way loose and sloppy fit. I'm going to put this chuck back on the shelf and replace it with a used one that has no issues.

Maybe you have a B22 taper?

http://www.stevenson-engineers.co.uk...nformation.pdf

Perhaps the taper on your arbor is a hair too long and it is bottoming out before it locks up. Gary P. Hansen

From your description, it sounds like your arbor isn't a #3 jacobs. A #3 Jacobs taper has a small end dia. of about ¾" and you said the chuck is just shy of accepting a 5/8" rod. Here's a couple more lists of tapers for reference;
http://www.newmantools.com/tech/taper.htm
http://www.tools-n-gizmos.com/specs/Tapers.html