Turning a radius on a barrel.

[Frank46]

Have a semi turned .375 barrel blank with 1x12 twist. And would like to know how to get the nice radius like on mauser military barrels from where the breeching part of the barrel butts up against the receiver then turns down to the cylindrical section of the barrel. Does one grind a special tool bit and take light scraping cuts?. I can grind one if needs be. And now for the rest of the story. I have a #4 enfield receiver that I cut down the left side wall and removed the charger guide. The receiver is basically the way I want it now and has been polished to 320 grit and I used one of the green 3M pads to blend the finish. I have hopes of getting Pacific Tool to grind a reamer for the .303 british cartridge necked up to .375 caliber. So if anyone can give me some ideas about chamber and throat length I'd be a happy camper. Still have to get some tooling for my lathe before starting out on this quest. The cartridge will be sort of a 38-55. I have about 500 IVI .303 virgin cases and will be using this brass for this rifle. I have JeffinNZ to thank for this. Should keep me broke and off the streets for quite sometime. Thanks,Frank

[Cap'n Morgan]

Grind a tool bit with a slightly larger radius than you want. The corner of the wheel on a bench grinder works great for this. Don't make the rake angle too large as this will increase chatter. When cutting, use low RPMs and use cutting fluid. Alternate the feed between cross slide and compound to keep chatter down.

Good luck with your project.

[Frank46]

Cap'nMorgan, Thanks for the tips. This is one project that will get done. Still have to get the wood (enfield buttstock and forend) as well as a bunch of parts. But bit by bit will get 'er done. Thanks, again Frank

[JIMinPHX]

... would like to know how to get the nice radius ... Does one grind a special tool bit and take light scraping cuts?

That would be one option. If your lathe is fairly rigid, then it's probably the easiest way to go. I've cut thousands of radius that way. The Captain's suggestions about easing in from both directions to keep your tool's surface contact area down is good advice if your equipment is borderline on rigidity. On my big greasy old Hendy, I could pull a 1/4" radius cut on a 17" diameter work piece with ease. My 13" Clausing cries if I try to pull a 1/8" radius in one shot. I need to pull the Captain's 2 direction trick with that one. If you are going to try that trick, then leave some lead in angle on the edges of the radius when you grind the tool bit. It's real easy to go in just a little too far with the bit & leave a nasty line just outside the edge of your radius if your tool has a sharp shoulder (don't ask, it's an expensive mistake that I've made more than once).

Another option is a little craftsmanship with a file & some wet/dry paper. With a little patience & a radius gage, I've been able to get good results on a lot of different parts where I didn't want to take the time to grind a special tool for a particular size radius.

The Cadillac rig would be a genuine radius tool. It's a little swivel jig that you mount on your tool post. It holds a single point bit (like an E bit). By setting the stick out length of the bit, you set the dimension of the radius. You swivel the bit back & forth to cut a perfect arc. That's how I used to make ball valve cores. It's a bit tedious, but it gives great results. A rig like that is more than a little pricey for a one-off job though.

[Jon K]

yep, radius tool can be pricey, but can also be made without too much difficulty. So for a one of a kind part, if the lathe is not rigid enough for the form tool to cut the radius, you might consider making a radius tool. just remember to just cut a little at a time.

Jon

[leftiye]

If all else fails, file it. (with a file, not in the circular file)

[Frank46]

Jim, Jon, and lefteye. Never tried using the radius trick. Would be worth a shot. The smaller radius's where the barrel steps down could and will be filed then cleaned up with abrasive cloth (not sandpaper- hate that word) and then the whole barrel given a go over with some 3M polishing pads I have to get a sort of matte looking finish.Just started playing around with the various grades of the 3M pads. Think they do a good job softening a polished finish so that it does not look shiney. Hey when you have more time than money anything to keep the mind going is better than nothing. I had taken the enfield receiver down to a 320 grit polish with 320 grit silican carbide paper then used the green 3M pads you get at home depot to sort of even out the finish/polish and they work pretty good. I may be wrong here, but sometimes a highly polished finish looks to glareing and looks a lot better toned down. Thanks for the tips. Just realized that this thread should have gone into the Barrel Works section. If the moderators want to move it to where it should be ok by me. Thanks,Frank

[JIMinPHX]

I find that a little motor oil on the scotch bright pads gives me a nice finish. I picked that trick up from a model making shop out in Brooklyn several years ago when I was there fixing a band saw.

[Frank46]

Jim, thanks for the tip. Will eventually be bead blasted. Helps to get rid of the scratches and evens out the finish. Frank

[quasi]

use a handgraver, like clockmakers use.