A few days back I asked about getting the wood discs out of a hole
saw easily. Then one of the replies inspired me - I'll make octagons
instead. That'll work, look better, be faster, etc.

Sounds easy. The discs were to be bases for profile chess pieces, 1
7/8" across. OK, cut a square 1 7/8" on each side, lop off the corners,
got an octagon, no prob. Prob.

I knew it would be a 45 degree angle, but how to figure how much to
cut off to have each side equal? Turns out, no prob. Drew a square on
graph paper, marked a line from corner to cornr. Measured 1/4" out from
each side of the lines, each way. Then measured one half of the width
of the square (would vary with the size of the square). Mark across,
and that'll show just how much to lop off. Repeat on each corner.

Now needed a jig to make accurate cuts. Had been gonna use the
mitre saw to cut with, but decided it'd be best all around using the
bandsaw. Took my graph paper with the sketch, made some guide lines,
didn't like that, drew out a new square, marked the corners, new guide
lines the opposite direction. Done. About 10 minutes tops.

Glued strip of scrap plywood on a piece of 1/4" plywood to be the
runner for the bandsaw. Just take it for granted I waited for the glue
to dry before going to the next glue step. Then ran the piece thru the
bandsaw to trim the edge. Then cut out the pattern, set it on the edge,
with the portion to be lopped off over the edge, then align a guide
along the top edge of the pattern, glue, clamp. Then same with the
other two edges, leaving the "back" edge open so a square can be slid
in.

I cut a piece of scrap OSB into a trial square with the mitre saw.
Got one size just a tad narrow. But put it in the jig, zipped thru a
corner, rotated the square, repeated until all four corners were lopped.
Looking at it, the octagon looked gread; but upon measuring it, four of
the corners were about 1/16" too short. But I figure that was from
cutting the one side too narrow, and once I get a cutting jig made
they'll all turn out the same. But, like I said, just from looking, you
can't tell. Beats messing with a hoesaw - for this project anyway.



JOAT
You'll never get anywhere if you believe what you "hear". What do you
"know"?.
- Granny Weatherwax

There's a faster way.

Make a bunch of oversized squares, and stack them up with double sided
tape or something (if you can drill a hole down the middle and bolt
them all together, even better.

Joint one "face" (edges), square an adjacent one on the jointer. Use
a table saw to square and true the other sides. Now you have a set of
perfect squares. Tilt your saw blade to 45 degrees, put the squares
against the blade (so they're also at 45 degrees) and set the fence to
just touch the corner of the squares. When you run the blocks flush
against the fence, it will cut off exactly the right amount off each
corner.

Also, for the math: http://www.delorie.com/quake3/octatrap/

Sun, Nov 25, 2007, 11:49am (DJ*Delorie) doth claimeth:
There's a faster way. snip

Don't agree at all. Plus your way is loads more complicated. I'm
thinking of adding to my jig the far end so I can square cut scrap using
the one jig. Remember, K.I.S.S.



JOAT
You'll never get anywhere if you believe what you "hear". What do you
"know"?.
- Granny Weatherwax