Removal of a Jacobs Chuck from an old 3/4" Skil Drill (OT)

Open the jaws and look down the opening. Sometimes there is an Allen head screw securing it on to the drill shaft. Randy
Guys, pls forgive the OT topic, but I need to get a 3/4" Jacobs chuck out of an old Skil Model 121 Special Duty drill (this thing is old, and large, and turns at 250 rpm, but looks like it could turn a 1" bit without a second thought), and can't figure out how to get the chuck out of the drill shaft.
I'm pretty sure its a threaded mounting, versus a tapered arbor, but I can't be sure. And I don't have a drawing or parts list for this old drill. I know how to get the chuck apart once I get it off the drill, but how do I get it broke loose?
Any help would be appreciated.... r/ Steve

That's a bit bigger than I've removed so this may not work but usually there is a screw in the center of the threaded shaft to lock the chuck on. Open the jaws all the way and look for a screw in the center. I will probably be left-hand threads. The ones I've removed had Phillips-head screws but as someone else mentioned yours may be allen.
After you remove the screw tighten the chuck on a rather large allen wrench. Give the allen wrench a tap with a mallet to break the chuck loose and it should spin right off.
Best Regards, Keith Marshall snipped-for-privacy@progressivelogic.com
"The universe is full of magical things, patiently waiting for our wits to grow sharper." -Eden Phillpotts, A Shadow Passes, 1934

Can you read anything on the chuck?
They often have a model number and often a capacity and mounting method like JT33 (taper).

Look very carefully down its throat. There's a good chance there's a retaining screw down there you'll have to remove before you can remove the chuck. The screw will likely have left hand threads.
Once you have the retaining screw out (if it has one), clamp the short arm of an Allen wrench in the chuck. Strike the long arm of the wrench with a hammer. (The chuck should have right hand threads, so strike it so it turns the chuck counterclockwise.) A couple of whacks should loosen it up and let you unscrew it the rest of the way by hand.
Gary

It may very well be a taper. My old 12A, 600RPM B&D 13/16" drill uses a JT6 with a positive drive key.
Get the numbers and info off the chuck.
GTO(John)

Guys, thanks for all the help! I guess I should have told you the obvious - there wasn't any bolt or hex head screw in the center of the chuck! That's why I have such a problem - I just did try the impact gun method, but hammering on a hex-key tightened up in the chuck with my 1/2" drive impact gun didn't faze it. All it does is loosen the chuck up from the hammering. And I was turning clockwise (assuming LH threads)!
The sucker MUST be screwed on... the numbers on the chuck are: JACOBS CHUCK #36B Cap 3/16" - 3/4" THD 3/4" - 16
By this, I guess it's a female thread (I think) in the chuck, threaded onto a stub shaft from the drill gearbox, that is probably left-hand threads, right? I think if it were RH threads, beings that the drill turns clockwise, it would then unscrew the chuck. Does anyone have a #36B chuck that knows if they are RH or LH threads?
This thing is kicking my butt. Usually, I'd simply apply the blue-tipped wrench to anything this recalcitrant, but I need this drill and don't want to screw it up!
Thanks again for all the great ideas - any more out there? r/ Steve

That's threaded all right. The threads are RH. Remember, the drill spindle turns clockwise into the chuck from the rear. From the front (jaw end) of the chuck, you'd turn it counterclockwise to remove it.
Here's what I've done in extreme situations--it always works: Take the drill apart and remove the rotor along with the entire gearcase. Tightly camp the whole assy, including rotor, in a vise between wooden block. Tighten a great big allen wrench in the chuck. Put a long iron pipe over the allen wrench and give it a heave (CCW from the front, again). Spraying PB Blaster into the threads a week before helps.
GTO(John)

John, that did it. Took said drill apart, bolted the gearcase cover together with some bolts and nuts, wrapped the nosecone with lead sheet, and tightened her up in the vise pipe clamp jaws. Inserted 1/2" drive hex key (9/16") in the chuck and tightened it down good. Got my 1/2" rachet and long cheater pipe - got up on top of the workbench and held the armature from spinning while I stepped on the pipe with my foot. It held my entire weight before it gave, but it did.
This was the last-ditch effort after I used the impact gun - going the right way this time.
Guys, Thanks a LOT! Now it's time to take apart the chuck... I found a great web site here: the Jacobs Chuck website has been taken off the web. Too Bad. This guy's done a great job on showing how to take these things apart and put them back together again.
Onward to making this thing into a drill press! Thanks again for all who gave me advice in this ordeal! R/ Steve Bremerton, WA

Thanks for the link. I've always wondered about how to take a chuck apart. Lane

Isn't this a great place to get incredible information and meet awesome people? Glad to be of help to someone and give back a little! Good luck on taking yours apart - I'll do mine this weekend. r/ Steve