I need an adapter (sleeve) to mount a front sight barrel band on a new/different barrel.

The barrel band is 0.920" ID.
The barrel is 0.625" OD.

The sleeve has to have a 0.148" wall thickness with a 0.625" ID and 0.920" OD.
The sleeve should be 1.00" in length.
The sleeve should have a single longitudinal slit in it the width of the saw blade (<0.10" wide kerf).  Alternatively, the sleeve could even be cut in half (two kerfs).
The sleeve should be made of stainless steel but aluminum is an acceptable alternate.

I don't have a lathe but do have a drill press.  Who, what where when why and how do I go about getting one made?

Can I bend a flat sheet around a 1/2" or 5/8" diameter mandrel?

Do I drill the 0.625" hole in a block, mount it in the drill press and machine the OD using a router (aluminum only)?

Do you turn a block to the proper dimensions on a lathe?

What would such a thing cost to have one made?

You can indeed form it on a mandrel .

First cut your blank at 3.14 X diameter of .625"
A little gap would be good in the formed part, maybe .032"
Trim the corners At 45 degrees @1/16"
You will trim the corners, so you don't garf the barrel on assembly

The edge radii will have to be former tighter.
Aluminum will be doable, stainless not so much.
300 series is easier than 17-7 to form.

But aluminum is easier for the home hobbyist.

I would form the edges, then hammer form it around the mandrel.
Hold it with hose clamps, and heat @350 deg for one hour.

OR ...
get a piece of tubing, and slice the gap with a jewelers saw.

McMaster & Carr sells tubular aluminum spacers.  They have some for $8 that are almost perfect - 1"L X 5/8"ID X 1" OD.

The only mismatch is the OD - 1.00" vs the 0.92" OD required.

Does this make sense?

1.  Mount it on a shaft and spin it in my drill press.
2.  Present it to a carbide cutter on my horizontally-mounted plunge router.  
3.  Cut the full length of the OD by lowering the quill on the drill press.
4.  Slit lengthwise after machining.

Your method might work, but it would be hard to mount the router vertically, and upside down to the degree of precision you're looking for. Also, drill press quills really aren't designed to resist side loads that well. It is not impossible for the chuck to disengage and fall out of the press while doing things like this. It happened to me when I tried to mill on my drill press, before I bought my mill.

How big of a hurry are you in for the part? If I have some stock (I think I do) I could whip one out on my lathe for you in a jiffy, but would need to do it this weekend. If you're not in too big a rush, I'd do it for free, less postage.

DeFens, thank you very much.  That's a terrific offer but I cannot accept.  This thread was not intended to get someone to do the work for me.  I was only wanting hints and tips on how to get it done.  Alternatively, I was hoping someone could point me to a place to buy the parts off-the-shelf.

Thank you, again.

<scurries off to order from McM-C>

<thinks to self, I'd better buy a spare>  

I mounted the router in a fixture that will present the bit to the rotating work piece.  The fixture is reasonably stiff but I wish it were more so.  Actually, the mounting plate may get replaced with something stiffer (thicker) before I get started.

I have a 3/8" end mill bit installed in the router (1/2" shank in the router's 1/2" chuck).  It is SHARP, as it has never been used before.

I need to reduce the OD of the spacer by only 0.080" (0.040" radially) to get down to the required 0.920" OD.

I thought I would take multiple, thin skin cuts.  I have to erect a Plexiglas safety shield, too, just in case things go south on me.

Does anyone have any thoughts on whether I should -

1.  Spin the router and only use the drill press to feed the part into the spinning cutter.

2.  Spin the part and feed it into a stationary cutter (cutter shape is not really designed for this option but it might work).

3.  Both - spin the part and feed it into a spinning end mill cutter.

Which will be safest?

Do I need cutting lube?  Is engine oil okay?

All done!

Worked like a charm!

The front sight is installed, leveled and aligned (concentric) with the rear sight.

I know, post pics!  That has to wait for tomorrow.

Did you use option 1, 2, or 3 above? I'm curious... 3 is what my intuition said was the only realistic option but I've never tried such a thing.

It is a little distorted (looks disproportionately larger than it really is relative to the barrel) due to the close-up shot but you'll get the idea.