So I have a new .22 upper I'm putting on my sbr lower for giggles.  My brother has one and it's fun as hell, and quite a bit cheaper to practice with than 300blk.  Got a 4.5 in cmmg barrel and will pretty much always have a can on it.  So I'm in the market for a ~6in handguard which will partially obscure the suppressor, a cool look imo.

I have a 15in strike industries key mod megafin rail.  Used it for the longest time, eventually swapped it out when I shortened my main AR.  The screws would not let go, I was young when I got it so had a pro do the assembly.  So the 7 tiny torque screws attaching the handguard got dremmel converted to flatheads so I could get the damn thing off.  Wierd size/pitch so theyre not readily replaceable.

I'm not super comfortable selling this handgaurd and it sits.  Until tonight.  Upon assembling my upper with the barrel nut from the strike I got the overwhelming urge to start another project.  I swapped the blade in the chop saw to a metal one and chopped the handguard at about 7 inches.

Used a table top grinder to smooth the chop saw a bit.  Thought of making another cut but then thought, duh, I have a lathe.  Cant find a way to chuck the thing up reasonably in the 3 jaw.  Think I could get the 4 jaw but dunno if that'd solve the issue plus swapping and getting the work proeprly indexed is my least favorite thing.

I grabbed some 4041, turned it down a bit to serve as a jig in place of the barrel nut.  Before I really got rolling my wife yelled at me for not studying for my final tomorrow.  Stopped for now but updates to come!

A four jaw independent chuck is practically a must for lathe owners. It will solve the workholding issue you're looking at there.

However - more than one way to skin a cat. Rig up a simple cat's head or spider for it. Basically drill a section of tube that the handguard fits inside with however many holes and tap for bolts. Mount the handguard inside via pressure from the bolts - preferably using some brass or copper or what you have so the bolts don't dig directly into the handguard. Don't over-tighten it either as aluminum extrusions like that are easy to deform.

Put the tube in the chuck and a steady rest and there you go.

ETA: Plus of course the cat's head ends up being used all the time. I have a bunch of different sizes and lengths I've made over the years since they're so cheap and easy.

Don't know why I didnt think of a cats head, I have one sized for barrels and it's invaluable for threading and the like.  Time to make another!

@Third_Rail
Here's mine, made from 2.5" NPS and a chunk of 1018. Just add more threaded holes, where you need'em.

Yup! That's just what I mean. Useful as all hell - and can be made pretty much any size/configuration needed.

It seems to be turning into one of those lost tricks sadly. Whenever it's applicable I like to pass the idea along as it's saved me any number of times on difficult setups.

Slight delay while I wait on the cats head materials come in sometime next week.  Wife is happy I wont be in the shop and I'll be studying.  Will update once I continue.

Current plan is to make the jig I started on and also do a cats head in a steady rest.  No such thing as too stable of work.  At this point I'll also swap in my 4-jaw cause why do it if I'm not going to do it right (amazing what sleep does to your decision making process).

I plan to face the end of the handgard up till I remove the partial keymod thats on the front.  Haven't guaged yet but looks to be 100 thou ish.  I'll also need to bore out some of the fins in about 100thou and back about 3inches.  Suppressor doesnt quite clear them.  Lastly I'm going to take the pic part back slightly on top at an angle as the slots up top did not line up with the key mod slots.  

I suspect the boring to be the most troublesome as I've never done a boring jump cut before.  Tips/tricks?

Also finish recommendations?  My current thought is basic spray paint.  I don't work with al very often and dont have the tools for decent finishes like anodizing.

Well, some progress.  The tube I got is not large enough.  I measured the handguard but didnt account for the fact that the handguard needed to be off center to account for the top pic rail.  Ordered a new pipe as I wont be able to do anything other than face the end.  So, some progress.

Also I promised pictures.  Quick mock up, wasnt able to thread the jig yet but soon.

I've made several Catsheads, but have never put the screws/bolts out of array, from one another. If you keep them on the same plane, moving one should only affect its counterpart. If you put them 45* from each other, you'll be influencing both the Y and Z planes. Make any sense?

Also, if you can, look again at my above pic and try to mimic. The Catshead threads directly to the spindle. No need to center it in a chuck or other. I have other ones that are made to go into the Steady, but that's only for long work or difficult opps. The one-piece design, threading into the spindle, is bar far an easier to use fixture.

If you want to put the Catshead in the steady, you'll first need to center it in the chuck. Then, put the steady around it and get it running true (sometimes making a new register, on the OD, is needed.), while still in the chuck. Once good, open the check jaws and slide the whole thing toward the tail. Get the work centered in the chuck and slide the steady/catshead into place. Center the far end of work, in the catshead.

Thread a catshead for the spindle, thats a helluva idea.  My old lathe manual had a spider guide and in it it had 6 screws in two planes 60degrees offset.  That's how I made my first one so I duplicated it.  Having 8 screws so theyre directly opposed is a great idea, itll mimic a 4 jaw.

I still have a 8in section of pipe I ordered.  I'm going to make a catshead as you described for future projects as that seems useful as hell.

I realized I was overthinking this a bit.  I dont need an offset center for facing the piece, so I put the spider in the 3jaw,set the handguard in the spider, and then immediately screwed up by not tightening the spider screws enough.  Put some brass mars on the handguard and put a small knick in it -_-.




After I put it in properly and got it dialed in facing it was a breeze.




Now I'll use the jig to hold the work off centered for boring.  I'll put it in the 4 jaw so I can take the fins down concentrically.  I'm worried having the work so out there but boring should have minimal deflection so I think it'll work out.



Lastly I'll finish the top rail in the mill with just a 60deg endmil.

My next project is making another catshead with the remainder of pipe I have and getting like a 5in diameter pipe and making another of that.  Having a big one on hand would have drastically cut down on machine time.  I still have very much to learn, I really appreciate the feedback.

Why didn't you leave the part in the catshead, for offset boring?

If you make the catshead from large OD pipe, just be mindful of your screw lengths and your ways. You might need 2 sets, for larger OD and smaller OD parts.

This catshead is not large enough.  I may wait for material to come in for another larger catshead but will likely finish this work prior.