what's my arbor?

What you need is a shell mill arbor as shown in the above link. You need to measure the hole a bit closer to find the correct arbor. You most likely have a 3/4" hole but it could be metric. Do you have a piece of 3/4" shafting you could slip into the hole? lg no neat sig line

"

Bingo, that's exactly it. Thanks.

With my digital calipers, the hole measures 19.96mm, so 20mm would be a good guess. (Yes, I know that a 20mm shaft shouldn't fit a 19.96mm hole, but I also know that calipers are not the most precise way to measure the ID of a hole.) It is definitely larger than 3/4" (which would be only 19.05mm). Is that fit critical, or does the screw center it and hold it in place?

The fit is extremely critical. However..that being said..its likely you can turn a bushing to fit a standard 3/4" shell mill holder. Assuming that the drive dogs are the same size or smaller than the slots on the back of the shell mill

Gunner

That rifle hanging on the wall of the working-class flat or labourer's cottage is the symbol of democracy. It is our job to see that it stays there. - George Orwell

What Gunner said. Shell mill arbors typically have a large screw that holds the cutter in place. It's very important that the cutter be driven by intimate contact with the driving dogs (keys) and that it not be a sloppy fit on the arbor. Otherwise it can shift on you while cutting and lead to some very unpleasant happenings. If, by chance, the cutter will fit the arbor, but will be a lose fit with the keys, be certain to load it against the driving side so it won't turn until it hits the keys while cutting.

I commend you on your good understanding on how calipers are not to be used for precision measurements. They simply are not precise enough for serious measurements.

Good luck!

Harold

Thanks, but you're too kind. I'm sure a competent machinist with appropriate tools could; but I don't own a lathe, nor any lathe tooling for the mill/drill. Nor do I have the skills to use them properly, I'm afraid. I did some machine shop work as a teenager, but that was a couple of decades ago.

Try this:

You do know that with a bit of ingenuity, you can so this sort of work on the mill..using it as an impromptu lathe of sorts.

Hell...send me the shell mill and the holder and Ill turn you an adapter for free. Just pay the shipping and Ill fix it up for you. Ive got other shell mills also I might be able to toss in the box on the way back to you also.

Lots of folks have helped me out a time or 4, so Ill be happy to pass it along.

Gunner

That rifle hanging on the wall of the working-class flat or labourer's cottage is the symbol of democracy. It is our job to see that it stays there. - George Orwell

That's an amazingly generous offer. I'll contact you in private email to follow up. Thanks!

I didnt think to ask..is that R8? Im in Reliable Tools a lot and run into lots of R8 shell mill holders (and shell mills etc etc etc. If you cant find what you need, drop me another email and Ill scarf one up for you. I can often get the "Brother in Law" discount on that sort of stuff.

Just be advised..that a lot of the small mill drills are really not rigid enough to do much hogging with a shell mill. You may..may be better off using a end mill followed up by a fly cutter if you are looking for a nice clean finish.

Shrug..but Im at your disposal.

Gunner

That rifle hanging on the wall of the working-class flat or labourer's cottage is the symbol of democracy. It is our job to see that it stays there. - George Orwell

R8, yep.

I'm only taking off enough to smooth a hacksaw cut: about a sixteenth of an inch. And it's brass.