tricky technique needed--curved cut

[Australopithecus scobis]

Greetings, I saw a nice wooden compass on eBay:

. I won't attempt ascii art. Having just finished my 28" frame saw, I thought I'd make a copy of the neat old compass. So, I hacked and whittled some scrap pine to get a feel for the process. One cut up between the legs to, well, the crotch. One cut to fillet the "hips". Now the tricky part: to get that nice round shape. A hole saw or fly-cutter won't do it. The round part only goes 3/4 of the circumference. How to make a curved cut? Abuse an appropriately sized gouge to pound straight in? Patient work with a #11 scalpel blade? The outside part of the top round is simple to carve. It's just the curved parts that overlay the opposite leg which pose a problem.

I could use two separate blanks, but it would be so elegant to cut it from one piece of wood. A simple straight cut would yield something that some of you may remember from high school geometry: that ugly thing with a rubber tip and a piece of chalk. Yuck.

Any ideas?

[Morris Dovey]

See

(Even more ugly than what you remember from geometry class :-)

I used the end of a pill vial for the top curve, cut both parts at once with a coping saw, and sanded 'em together, too.

Tain't pretty - but it draws well...

[Bill Rogers]

It is nice!

Doesn't it go all the way around, so deep? Then you can finish with a rasp/file/sandpaper ...and patience, which a lot of old woodworkers had. So, I'd start it with a curved wheel cutter for the top rounded shape then rasp down the rest.

P.S. [A compass is a direction finder.] I use drafting compasses or trammel points, but still love old tools like the one shown.

Bill.

[J T]

Sat, Aug 14, 2004, 9:52pm (EDT-1) [e-mail] (Australopithecus=A0scobis) hails us: Greetings, =A0=A0=A0=A0=A0=A0=A0=A0I saw a nice wooden compass =A0Any ideas?

Buy one. I got a nifty plastic compass, that works great, for about $1 at an office supply store.

If I wanted to make one, I'd make a nice master, maybe use a hole-saw cutout for the round part (glued to the leg), use my router table to rout out a couple of copies, then sandpaper fo a final shape. No prob. Or, cut out most of the legs, and just route the round part. No prob.

JOAT You have to kill pessimists, but optimists do it themselves.

MUPPET SHOW THEME

[Australopithecus scobis]

Brutal, yet effective.

[Morris Dovey]

I should have looked at the pix before I posted - sorry.

I think this might be more a layout problem than anything else, although careful work will be needed.

You might think about laying this out so that the ends of the legs fall at the edge of a board; and drill the legs first (to avoid splitting). Then use a Forstner bit to drill the flats of the joints and a small brad point bit for the pivot screw hole. Once that's done, I think I'd saw out the two blanks on the BS. A

1" belt sander or spokeshave might work for final shaping of the legs; and you might even be able to use the belt sander to round the outside face of the pivot.

Good luck on finding a similar brass screw and high-angle wing nut.

I'm tempted to try a divider (no metal point or pencil) version on the CNC out of ipé - except that I'd never be able to give myself permission to actually /use/ it...