1/2" straight shank to 3/8 x 24 threaded arbor

It wouldn't be all that hard to make one from a typical straight shank for drill chucks, assuming you have access to a thread cutting lathe. They aren't typically hardened, and if they are, it's not too hard to machine them. Buy one that has a taper larger than the thread you desire, then turn and thread it to fit the chuck as required. That's assuming you can't buy one that fits.

Harold

I imagine you wouldn't even need a thread cutting lathe. Any lathe should suffice to turn the end to the 3/8-24 thread major diameter, followed by the application of a quality external threading die.

- Michael

I can't recall seeing them in catalogs, but that doesn't mean they don't exist smewhere. Like Harold suggested, nearly any adapter can be made or modified to fit, when a lathe is accessible. The 3/8"-24 arbors are available with various shank tapers. One with a Morse

2 taper could be turned down to 1/2" straight (and then shortened) if the taper isn't fully hardened.

WB ............

Never done it, but could you pick up a half dozen "busted" drill motors at a flea market for a buck, and use the spindle from one of them, almost ready to go. Heck, unless the chuck you have is "special", just use the assembly from one.

Gotta admit to having the same item you're making in 1/2, 3/8, and

5/16 shanks, the standard (to me) R-8 (end mill shank) collet sizes. Handy like a thumb.

Brian Lawson, Bothwell, Ontario.

Just went through this. For the 3/8 thread, buy a shoulder or stripper bolt of the appropriate length/diameter/thread. Use a carbide tool and high speed with light cuts to machine off the head. Insert modified bolt in chuck.

Thanks for all the tips. I wonder why these are so difficult to find?

Guess I'll have to make one. The bolt idea is quick and easy, but that doesn't leave me with a 1/2" shank, unless I am missing something.

I considered just taking a 1/2" peice of round stock and machining one from scratch, and then buying a die for the threads. Though I may go the route of buying a MT2 to 3/8-24 arbor and turning down the MT to

1/2". That should be a piece of cake as long as I can hold the piece in my chuck well enough to turn down the whole taper. Maybe I can mount it into my drill chuck first, then hold the drill chuck in my lathe chuck. Hmmm.. I'll figure it out.

Thanks again.

You missed his point. Use a SHOULDER bolt with a 1/2" shoulder and 3/8" thread, then machine off the head and you'll have a nice ground 1/2" shank, just exactly what you want.

GWE

Yes I did miss that. Thanks, now that is very simple!

Only if you don't care if the chuck runs out wildly. By chasing the thread, you're assured it won't, assuming the arbor runs true when the thread is chased. It borders on the impossible to get a thread to run well enough with a die.

Harold

If you choose to go that route, I'd highly recommend you turn the arbor between centers, so you end up with the desired concentricity and perpendicularity. It's most likely the arbor was made that way, so you'll retain the original precision by altering it in the same fashion.

Harold

The problem with that idea is that stripper bolts (shoulder bolts) are centerless ground, with the threaded portion generated by either a die head, or the thread rolled. They are not generated around a true center, as might be desired. There's no guarantee the chuck will run true as a result. The slightest amount of deflection will manifest itself in a badly aliened chuck, especially when holding a long drill.

Harold

I gather you have a lathe. I suggest you make it from steel rod. As Harold said, it doesn't need to be hardened. I'd like to make two points: You want to have a shoulder that the chuck screws up against otherwise the chuck will never in a million years run square to the shank. You want a short unthreaded, accurately machined section between the threads and the shoulder. This should be a good fit in the short unthreaded bit in the outer end of the chuck mounting hole. This is because I have _never_ seen a threaded attachment that centered accurately without such guidance.

In other words, when you screw the chuck onto the arbor, the un-threaded just-fit part will force the chuck to center on the arbor and the shoulder will force it sit square.

I know this because before I had a decent lathe, I tried to make such adapters from bolts and never, ever, got one to run straight and true.

You'll have to start with 3/4" stock for the 1/2" thread in order to get the shoulder.

BTW, I might not get to it for a while but I'm about to make an adapter using the above technique to allow me to mount a small three jaw chuck onto a taper than will fit my live center. This is for supporting long pieces at the tailstock end that, for one reason or another, I can't center drill.

Ted

Thanks for the tips. I think I may just go with the MT2 taper to threaded adapter as mentioned before. The drill chuck alignment will be perfect, and my only machining operation would be turning the MT down to 1/2" accurately. I feel my lathe can do this with no problem.

I can also make one from scratch, but I am woried about the accuracy of using a die by hand to cut the threads. Though if I make a proper shoulder as described above, that may take care of any error while cutting the threads.

Terry

I answered my own question. I thought I had searched everywhere for this adapter, but one place slipped my mind, JL Industiral Supply. They have them in stock for $17.00.

I'll be ordering a couple of these. Hopefully they are decent being an import brand.

Terry

I FOUND a precise 3/8" thread on a 1/2" ground shank. It was the piece the chuck screwed on in a junked drill. I did have to press the gear off the shaft and polish out minor serrations under the gear, but it allows me to use my 3/8 chuck in the 1/2" collet on my mill.

They also seem to be looser than typical threads, perhaps to accomodate the misalignment between threads and body when mounted in a counterbored hole. Also the diameter of the shoulder is 2-3 thousandths under nominal. And most chucks with threaded mounts are fine threads-shoulder screws have UNC threads.

Ned Simmons

Drill chucks from busted drill motors, along with the chuck shaft and first gear as a handle, are handly to have around the shop for lots of things. Think of it as a large version of a pin vise.

Need to shorten a cap screw on the belt sander? Chuck it in the drill chuck and never burn your fingers again. Tool bit grinding? Chuck it in the drill chuck.

Etc etc

Gunner

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner

The good-quality 1/2-20 Jacobs chuck that runs true on my 6" Sears lathe shows some wobble on all the import straight and Morse arbors I've tried it on.

Jim Wilkins

Also, the standard shoulder screw is coarse thread. 16 instead of 24. A stripper bolt might do, so I created a corporate account at a fastener company and my quote 103 should be back Monday.

Doug