Octagonal barrel dimensions

[eddillon]

Anybody out there have a quick method of calculating the "across the flats dimension based on the diameter of the round barrel blank.  Trying to figure the least amount of material to be removed to make a swamped pistol barrel for a Boutet build.  Also looking for a Damascus blank or a 9-10 inch piece of an old Damascus barrel that can be made into an 8.5 inch 52 cal. barrel.

[Kermit]

Ed--use this. Enter "A" and all the other dimensions magically appear. Is this what you need?

http://www.pagetutor.com/octagon_layout/

I'll keep looking, since this one's really for large octagons. Works for furniture, gazebos, and such.

Addition: this may work better for you. It's the method I use for oar looms, spars, chisel handles, and other small stuff.

http://www.popularwoodworking.com/woodworking-blogs/chris-schwarz-blog/octagons-made-easy

If you prefer to use a calculator, this might help:

http://www.had2know.com/academics/octagon-measurement-calculator.html

[eddillon]

Thanks Kermit.  I'm getting too old to remember my trig from college.

[Kermit]

There was trig in college? 

[eddillon]

Part of calc in the mid 50s.

[Charlie B]

Generally you need 1/8" extra round stock to cut flats. I.e.1-1/8" round makes 1" across flats. This works up to 1-5/8" round stock.