cutting an octagon barrel
What is the best way go about milling a round barrel blank to tapered octagon? Rotary table with a tail stock?
Spin index on one end with the other in a milling vise?
Mike Hunter will have more insight, but either method will work. The RT and tailstock might prove a bit more rigid.
The problem comes with the length of the barrel compared with the mill table and travel. You might have to make a sub-base to mount things on and move it to cut the full length of the barrel.
I have only half-octagoned barrels, and not tapered at that.
I like the method Jim describes with the sub base and then moving the whole works. That way you don't loose position. I would definatly use the tail stock, I am thinking an adjustable tail stock so you can get the taper you want and keep everything more rigid. Just curious , are you starting from scratch? what type of steel are you using? or are you buying a ready made barrel?
Both ways will work, I'm not overly crazy about spin indexers, they always seem a bit flimsy to me. I use a Hardinge 5C Collet indexer on one end and a tailstock on the other
Biggest piece is how much real estate you have on the table, you'll be surprised how quickly you use it up. On a 42 inch Bridgeport table, a 26 inch bbl will be very tight.
Your barrel needs to be well supported in the middle, either with a couple of vises or a couple of angle plates.
Also keep in mind that you really need a center on both ends, remember all measurements need to be from the bore.
Hope this helps
I should have been more specific
The rifle is a low wall I want to rebarrel to 218 bee with a 1/2 octagon barrel. I was thinking of turning the round portion as a "target" and then cutting the octagon. The total length of the octagon is no more than 12" and my mill will handle that with no problem.
Most of what I do is drilling/tapping, cutting dovetails, and other "short" jobs. I've just never profiled and octagon barrel.
One set up would be to hold the round section in a milling vise with the chamber end in the spin index or rotary table. That would seem more rigid than a tail stock.
The half octagon does make life easier, and working from a tapered round barrel will help. Just about any of the setups described will work, but holding a taper in the vise presents a few problems. The tailstock, if nothing more, will help insure everything remains on center with the bore as Mike mentions.
When turning the taper, leave a step in diameters to leave more material for octagoning, and leave a bit more on the length for a wedding band transition, it really adds class.
That will be a pretty gun when done. Please show us some photos.
12 inches should not be a problem; and the way you proposed will work fine.
On full length octagons the tailstock is primarily for alignment (minimal holding) of the bore, and to set over the taper. Primary clamping is a couple of mill vises or angle plate.
When I do ˝ Octagon BBLs I mill the octagons first then turn the round portion.
For full length octagon, couple of ways to do it.
You can mill the top with a face mill by adjusting the height of the bore, using the tailstock raise or lower the height to get the correct taper. The mill vises are loose on the table, set the taper (height), clamp the vises to the BBL then clamp the vises to the table. You need to loosen the vises from the table each time you index.
Another method is to use angle plates. Again set the taper using tailstock, offset the tailstock to the correct taper, then bring the angle plates up against the BBL. Clamp BBL to angle plates (I use “clamping buttons”), then clamp angle plates to table. Use a shell mill and mill the flats from the side. Again you need to readjust the angle plates each time you index.
For a quick /easy taper adjuster, I’ve mounted a boring head with a center on my tailstock.
If you want to spend some time and end up with a really pretty barrel, mill the flats from the side with a large diameter shell mill and leave the octagon to round tulip at the breech end like Ballard used.
Thanks for the tips
I was going to do the ballard style breech end, but I had forgotten about the wedding ring. That would really look great.
I'll set up the barrel like Mike Hunter suggested, with an angle plate or two backing up the cut. The boring head with a center trick is one I've used on the lathe for tapers.
Cutting an octagon barrel
I made a set up to mill octagon barrels. You must have a means of support. The supports also have to be adjustable. I have photos but don't seem to be able to post them here.