I've done a few round to octagon machining. With 1" flats I've always done it on the mill with the side of the cutter. But on this next project I'm thinking about using a Fly-Cutter and milling from the top. This would allow the barrel to sit flat on the table for extreme rigidity. Yes/No? 
How do you mill from round to flat? In this article you can see a recent set up I used..... (You need to Login or Register to view media files and links)

I side mill them clamped down to the table. I've found that draw filing them is easier with a side mill finish than with a rotary mill finish.

I used to do it held by my rotary index and a center with a support half way. I used the 90° attachment on the Bridgeport and a 2" spiral milling cutter and did it from the top. The set up makes it lots easier to taper and do a half round, half octogon leaving a nice transition radius between the round and octogon. The set-up also leaves the barrel in alignment  to mill raised sight ramps and  base (s) when material was left on the correct spots for fancy work. As one other poster said if nothing else it is easier to draw file the flats when the machine marks are not a spiral on the flat.
 

All good suggestions. Thank you. This barrel will be a Octagon to Round...Only 13" of a 30" barrel will be octagon and no transition at the receiver end. Octagon right up against the receiver.

5C collet spin indexers work.  Two aren’t necessary.  One end can be held by a center, but that is less ridged.  I usually put down paper towels over the ways because it is going to make a TON of chips.  Second picture is a couple light passes worth of chips.  At least the chips that didn’t end up on the floor, walls, ceiling, and everywhere else.

RoyB wrote on Jul 17^th, 2026 at 9:08am:


Just one?