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Kurt Loup
05-19-2008, 02:16 PM
I need to make a drawbar for my South Bend 9" Jr with a 3/4" through spindle hole to hold a MT 2 ER collet chuck. The chuck requires 3/8" x 24 threads. Is there anything special that needs to be machined into the drawbar to center it in the spindle? From the photos I have seen of drawbars, it doesn't appear to be needed. I did notice on one drawbar, a taper was turned on the collar that bears against the rear of the spindle. I assume this is to help center the drawbar in the spindle. Thanks for any advise.

Kurt

SGW
05-19-2008, 02:54 PM
As far as I know, all you need is to make sure the outboard end is centered.

You should probably screwcut the 3/8-24 thread to be sure it's concentric and not cocked.

JCD
05-19-2008, 05:22 PM
I have used the same Collets in a vertical mill and lathe with success.
The draw bar had an external and face bearing surface. The external bearing was used to center the draw bar, so that it would be centered in the collet, and so it was centered in the spindle, probably to reduce vibration caused by an off centered, or an out of balance condition.
A word of caution in using #2 MT collets. They tend to tighten very rapidly and as the #2 MT is a locking taper, the collets can get stuck in the spindle very easily. So the answer is... be careful not to over tighten.
Normally the SB lathe will have a spindle through hole large enough to accept an adapter other style collets. You may want to think about other style collets for the lathe application. I believe the 3C collet will fit the smaller through hole spindles, They are about $20.00 ea. It's your money, your machine and your project. I'm just drawing on my experience. There are also probably 50 to 100 guys out there who love #2MT collets, so you will probably get about 50 to 100 opinions. Good luck , have fun.

Kurt Loup
05-19-2008, 05:54 PM
Thanks for the info. The collet holder is similar to the one below, but with a MT2 shank. JDC, was the external bearing face tapered to center it in the spindle or was the drawbar turned to fit the interior diameter of the spindle without play?

Kurt

http://littlemachineshop.com/Products/Images/480/480.2888.jpg

JCD
05-21-2008, 08:36 AM
The OD of the draw bar was turned to fit the ID of the spindle, no taper.

Hope this helps, have fun.

ptjw7uk
05-21-2008, 09:00 AM
the drawbar I made for my lathe I used ready made threaded rod so for the outer end I made a washer with a tapered section to pull the threaded rod central - worked for me.
On the mill I nachined a imperial draw bar from heaxagonal bar to a snug fit in the mill, a plus factor was that it was much shorter in legth than one for the lathe.

Peter

Kurt Loup
05-21-2008, 09:29 AM
Thanks for the help.

Kurt