Clamping Cauls

All right, I've done a bit of googling and found a few different techniques for estimating how much crown to use. Now for the math jocks. I'd like to have my cauls be of a constant radius, so I can use the whole length or any portion thereof. If I want to have a 40" length with a crown of 1/10" in the middle, I'm drawing an arc of what radius? Thanks.

JP

| I'm thinking of making some dedicated clamping cauls out of maple, | and was wondering about dimensions. Say I use 8/4 stock, how | "tall" should they be, and given that thickness and height, to what | radius should I round them? (They'll be 40" in length.) I'm | planning on making up a template for them, and then shaping them | with a router. Any rule of thumb for this? (heh. any boondock | saints fans?)

You can find a "rule of thumb" at

Radius = 2000.05 inches.

You can cut them much faster on a table saw. Put one board on top of another, screw through one end into the board below. Now, etiher by hand or using C clamps or whatever, bow the top board so it's now-bowed edge extends over the lower board. While it's stressed like this, screw down the other end to the lower board. Then cut on tablesaw, & voila, one curved board. (Not sure, credit to FWW I think)

Wouldn't that result in a board that is 'skinnier' in the middle? I thought that for a clamping caul you wanted the board to be 'thicker' in the middle.

Maybe I'm confused about what you are describing, though...

Mike

Depends on which side of the bow you cut on. Cut on the concave side, and it's thicker in the middle; cut on the convex side, and it's thicker at the ends.

You do.

The description sounds like cutting on the convex side, which is not what you want. Using the same technique, though, and cutting on the concave side, seems to me that it should work just fine.

Oh. I'm gonna need a bigger trammel. JP

Maybe someone with a CNC router could start selling templates. Until then, I think this is the way to go.

JP

PS: I'll give someone $40 for a 4' CNC'd arc with a 2000.05" radius. Plus shipping. 3/8 or 1/2 inch baltic birch or similar plywood. Seriously.

| On Nov 29, 11:29 pm, snipped-for-privacy@fellspt.charm.net () wrote: || You can cut them much faster on a table saw. Put one board on top || of another, screw through one end into the board below. Now, || etiher by hand or using C clamps or whatever, bow the top board so || it's now-bowed edge extends over the lower board. While it's || stressed like this, screw down the other end to the lower board. || Then cut on tablesaw, & voila, one curved board. (Not sure, credit || to FWW I think) | | Maybe someone with a CNC router could start selling templates. | Until then, I think this is the way to go. | | JP | | PS: I'll give someone $40 for a 4' CNC'd arc with a 2000.05" radius. | Plus shipping. 3/8 or 1/2 inch baltic birch or similar plywood. | Seriously.

Would you like a 40" arc in a 48" piece - or the arc across the entire

The 1/4" material is less expensive to buy and ship; and can be used to produce additional templates out of whatever you'd /really/ like. [ B'sides, I already have the hardboard in the shop :-) ]

-- Morris Dovey DeSoto Solar DeSoto, Iowa USA

I think you're all getting carried away. I just took a hand plane and c= ut what seemed to be adequate. Been using them for years. Don't overcomplicat= e things.

--=20 It's turtles, all the way down

It'll cost you a hundred bucks just to turn mine on.

Take a look here

whatever, if one board is skinnier in the middle, waht does that make the board it was cut from? Actually, it doesn't matter, IMHO ideal would be a caul that was curved and of equal thickness & width (Kind of like HD lumber but more consistent :) ). Sometimes with a caul, you may want to put a clamp at each end; then you want the convex side facing against the "clampee" Other times, a single clamp in the middle will be adequate; then, you would want the concave side of the caul against the workpiece.

| It'll cost you a hundred bucks just to turn mine on.

Your machine beats the daylights out of mine for precision...

...but mine turns on a lot easier :-)

-- Morris Dovey DeSoto Solar DeSoto, Iowa USA

There are other methods to use. A trammel is great for a direct cut, but there really are other ways to get this.

FWW had an article in there mag a couple of years ago called "Cutting big curves"

Wish I had one like yours sometimes though.

You beat me to it. For that slight of a curve and given that cauls are not german timepieces, eyeball it with a #5 and start gluing.

Dave Hall