JT 2 1/2 arbor

[schmidty13]

I was given a decent 16 speed Taiwanese made floor drill press. I'd like to use it but the spindle is JT 2 1/2 and the previous owner kept the arbor. Does anyone have an arbor -with or without a drill chuck- laying around that they'd like to part with?

Moderator's Comment: This thread was originally in the "Machine Accessories Wanted" forum. Toward the end of this thread, the conclusion was reached that the drill press in question had originally come with a 2MT to 2-1/2JT arbor installed in the spindle. And the factory erroneously made up the specifications tag to say that the press came with a (male) 2-1/2JT spindle. But it took a while to reach that conclusion, in part because Jacobs apparently discontinued the 2-1/2JT taper more than 70 years ago. So there was first the question as to whether 2-1/2JT even existed. And in part because at least one other such machine was reported as on hand.

 

[Nogoingback]

What's a Jacobs 2 1/2?
The reason I ask is that I'm looking at an older Jacobs catalog and there is no 2 1/2 listed. There is
a 2, a 2 short and a 3.

 

[schmidty13]

2 1/2 Jacobs Taper

I'm rebuilding an old Drill Press that has a chuck which is labeled 2 1/2 Taper. It appears to be a Jacob Taper 2 1/2. Yes there is such a thing. Below is a table I found at Wikipedia. No one carries JT2.5 Drill Chucks. It looks like the JT6 is very close. Do you think it will be OK or do I...

www.practicalmachinist.com

(Not my post, just an illustration that they are out there)

Here's a chart I found on the website of H.H. Roberts Machinery. As you can see, it's very close to a JT 6, but is it close enough?:

 

[MSBriggs]

If the drill press spindle is hollow, to take an arbor, it would typically be Morse taper. The end of the Morse taper arbor could have a Jacobs taper for the drill chuck. Obviously the Morse taper has to match the spindle; but you then have choices for which Jacobs taper to have on the other end of arbor. Which could be picked to match a drill chuck that you already have, or that is readily available. Some drill presses don't need an arbor, directly having a Jacobs taper on the end of the spindle. Are you sure that you need a JT arbor?

 

[projectnut]

If I'm understanding you correctly you're saying the taper in the spindle is a Jacobs 2-1/2. Al the Taiwanese drill presses I have use either a #2 or #3 Morse in the spindle, and a Jacobs taper on the chuck. Have you actually measured the spindle taper, or are you going on the word of the previous owner?

In any case according to a discussion on another board the Jacobs 2-1/2 is nearly identical to the Morse #6. They are slightly different in length, but only a little over .0001" difference in the taper. Here's a link to that discussion:

2 1/2 Jacobs Taper (practicalmachinist.com)

 

[schmidty13]

Yes I'm sure, and the link you posted is the same one I did. It's very close to a JT 6, but the OP said this:

I received the JT6 chuck from Enco and it does not fit on my drill press. It appears to be close but those few thousands of an inch matter. I can feel a slight rock if I push it side to side after mounting it. I'm debating whether to try something irreversable like lapping the nose of the spindle or grinding the chuck to be JT2 1/2.

To prove I'm not insane:

 

[MSBriggs]

...
In any case according to a discussion on another board the Jacobs 2-1/2 is nearly identical to the Morse #6. They are slightly different in length, but only a little over .0001" difference in the taper. ...

From the table posted above, a Jacobs taper 2-1/2 is similar to a Jacobs 6. A Morse 6 is big -- 7.25" long, versus JT 2.5 at 1.055" long.

 

[wa5cab]

Unfortunately, it would appear that Jacobs quit making chucks to fit a 2-1/2JT sometime prior to 1961. I have a price list and catalog for that year that lists at least one chuck with 0JT through 6JT plus 2shortJT, 33JT and EJT only. Your best bet may be to un-install your drill press spindle and take it to a shop and have it re-ground.

 

[martik777]

Mine is also a 2 1/2,made in 1985, I replaced it with a keyless JT6, seems to work ok

 

[wa5cab]

Well, if that works, it would certainly be easier and cheaper.