Make Your Own Curved Clamping Cauls

[Tipton Lum]

I had an upcoming job requiring almost 30 slab doors, ¾" panels, ⅜" solid edge banding, four sides. I needed curved cauls of several different lengths of for the glue up. Two issue presented themselves. How to get the ideal curve for each length, and how to produce a bunch of them quickly. The methods involving hand planes, bandsaws, jointers, and sanders did not appeal to me, to much futzing. I wanted a setup that was repeatable and didn't involve a lot of individual handy work.

Steve Elliott describes how he bends and marks the stock for the curve, but he then shapes it by hand. Good on the curve but not the shaping. Wes Grass, post #10, cuts his while still bent. Now we're getting somewhere. {On Wood Central - Moderator}

In my shop, jigs are made from scrap, cobbled together with staples and sheet rock screws. If glue is involved, it's hot glue. They are made for a specific task and are pretty much a temporary fixture. After it's used, it gets cut up and trashed. Rare is a jig that makes it on the wall.

This is the jig I came up with to repeatedly cut curved cauls on a tablesaw. The "sled" is ¾" ply with a ¼" ply support stapled to the underside.

http://www.sawmillcreek.org/attachment.php?attachmentid=274606&stc=1

The "clamp body" is a bock of scrap with a hole, screwed to the sled. The "clamp screw" is a ¼" carriage bolt with the head cut off, heated and bent. The bend continually straighten. Bigger would be better, or a better bolt.

http://www.sawmillcreek.org/attachment.php?attachmentid=274607&stc=1

Drill a hole in the middle of the stock, put a spacer at each end of the blank and tighten the "clamp" until the stock just touches the side of the sled. Notice the stock lifting off the ¼" base.

http://www.sawmillcreek.org/attachment.php?attachmentid=274608&stc=1

More scrap and a screw makes it sit back down.

http://www.sawmillcreek.org/attachment.php?attachmentid=274609&stc=1

Set the tablesaw fence for the narrowest width of the sled and stock (measured by the clamp), and run it through the saw. To be sure the blade trims the entire edge, scribble a pencil in the middle. If the pencil mark is still there, nudge the fence over and take another pass.

http://www.sawmillcreek.org/attachment.php?attachmentid=274610&stc=1

This is what the curve on one of my cauls. This method gave me the most even clamping pressure of all the other methods I experimented with. Another reason I like this is you can rework the same blank. For a 54" caul, I started with ⅛" spacers and work my way up to a ¼", using the same blank. I made two other lengths using different spacers. For 40" I used 3/16, and 28" was a fat ⅛", 4/5 oak. Your milage will vary depending on wood and size.

http://www.sawmillcreek.org/attachment.php?attachmentid=274611&stc=1

After the jig was made and the stock prepped, it took less than 2 minutes to shape each (virtually identical) caul. No, This jig is not hanging on the wall.


This is my first post here. I have used this site as a reference many times over the years. Just paying it backwards. Hope this is of help to someone.

[Bill ThompsonNM]

Welcome to the Creek! That's a well thought out idea.. Thank you, I'll be using it. I think I even have an L bolt that would be perfect...

[Jacob Reverb]

Awesome first post and very neat idea. Thank you for posting it up. http://s3.amazonaws.com/advrider/beer.gif This thread is getting saved!

[Mike Henderson]

Good idea! Thanks for posting.

Mike

[Prashun Patel]

Great idea. Thank you very much.

[Joe Hillmann]

That looks like a really good way to make a caul that has even clamping pressure along it's entire length. I may have to make a few.

[Bill Huber]

Welcome to the Creek !!

Great way to make the cauls, it sure beats the way I have done it.
This will give me something to do in the shop this weekend.

[Bill White]

Now that's a feller usin' his head.
Well done.
Note to self:
Why the heck didn't I think of that? :confused:
Bill

[Ben Martin]

Sweet!

Now just to add the dado and rabbet so that you clamp can be captively held in the ends...

Ben

[glenn bradley]

Cool idea. I template route mine but, your idea actually deals with the caul under stress and takes the individual characteristic into account.

[Tipton Lum]

In the past, the length of time a glue-up was in the clamps, and the number of clamps I had, was kind of self monitoring. Run out of clamps and the first glue-up was ready to come out freeing up clamps. Using cauls, I need only 2 clamps per door and the glue-up goes faster too. I run out of cauls before running out of clamps. I NEEDED MORE CAULS!

Version 1.0 has long been "re-purposed". It had a tendency to try and tilt the blank. v2.0 has corrected that. I think I would be able to cut a 2x4. I'd try but there are none laying around the shop right now.

The flat side of the cutout was a plunge cut on the tablesaw. That flat area and the back of the upper piece need to be flush. Don't worry about the front side being aligned, running the whole jig it through the tablesaw will true it up. This blank was 66" x 1-7/8", 5/4 oak. When tightened in the jig, the bottom is not in contact with the table surface. It cut fine.

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This time it has a full length, 1-1/2" high face.

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The clamp is 5/16" all thread with an 1/8" hole drilled through it.

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The base is cut out to allow tightening the nut. A ratcheting box end wrench is real handy.

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One hole for the all thread, one for the retainer pin (a drill bit).

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Loose.

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Tightened.

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Cut.

[Chris Friesen]

Very nice!

The only improvement I can suggest would be to have a method to tension the caul to the average tension of the clamps you're going to use rather than using a fixed displacement. That way you know that when you tighten down the clamps it'll give even pressure across the whole surface.

[Prashun Patel]

Reviving an old thread...

I am gluing up a 72" countertop of about 23 x 2" sapelle slats.

The curved cauls have made gluing up a real joy. I made mine from 2x4 scraps. I found it easiest to work in 24-36" sections, and to clamp the cauls in the middle temporarily while I attach pipe clamps at the ends. This stabilizes the cauls during tightening, and also evens the gap before tightening so you don't have to muscle one side to close a huge gap.

Thanks, Mike!

[Jared Sankovich]

I had a bunch of 48" cauls to make for a 11' dining table and remembered reading this thread. My version used a washer head spax screw instead of a threaded rod. It worked great and took no time.

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[Joe Wood]

Could someone post some pics of these curved cauls in use? I don't understand using them on flat stock.

[glenn bradley]

Not actually in use but, this demonstrates what happens. The first pic shows the curved side down and only the center contact point in applying pressure.

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If the bench top was a long area to be clamped that you could not normally reach with typical clamps, tightening the clamps creates a line of pressure along the caul.

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I'll see if I can sind a shot of them in use on a carcass.

[Joe Wood]

Yeah I don't understand, it applies pressure at one point but why not use a flat clamp block and apply pressure across the whole surface?

[glenn bradley]

Because the flat block will apply pressure at the clamp points and then less pressure as the block surface is farther from the clamping point. The bow in the caul makes up for this by applying pressure somewhat equally over the entire length. At least, that's the theory; works in practice for me.

Ah, found one. You can see the caul at the top center. I am using one clamp at each end to clamp the 24" length of the panel to divider dado joint.

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[Joe Wood]

That makes sense! You'd need a flexible piece of wood not too thick?

[Joe Wood]

What I do is use ipe clamp blocks that hopefully don't bend much. I need to look into these curved cauls :-)

Trial and error about getting the curve just right?

[jack duren]

Is this another version of Bow Clamp?
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[glenn bradley]

What I do is use ipe clamp blocks that hopefully don't bend much. I need to look into these curved cauls :-)

Trial and error about getting the curve just right?

Depends on the material. On this Pecan set I use 1/8" on the 24", 1/4" on the 36" and 3/8" on the 48". I believe the commercial ones made of maple use a more pronounced curve.

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I just sand them smooth and apply wax. I re-wax about once a year.

[Jim Becker]

Is this another version of Bow Clamp?
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Yes...this thread is about "rolling your own"...cutting the curve.


That makes sense! You'd need a flexible piece of wood not too thick?

Glenn's explanation is spot on...the "bow clamp" (commercial or home-made) distributes pressure across a long space with only two clamps required; one at each end. This is very convenience for wider glue-ups where the wood has it's own ideas and doesn't want to stay level at the individual joints across the workpiece. The commercial version that I own have a cross section of about 2+" x 2+", give or take and are made from hardwood. You don't need or want something "super flexible" because you want the clamping action to do the work and you always want them to spring back completely when the clamps are released.

[Jared Sankovich]

Could someone post some pics of these curved cauls in use? I don't understand using them on flat stock.


Two opposing curves create a flat plane under compression

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These are 2.5" at the center, made out of 2x framing material 48" in length. The curve is about 3/8 per side or 3/4 for the opposing pair. It's enough pressure I'm tearing the threads up on those bessey clamps

[Jared Sankovich]

Is this another version of Bow Clamp?
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Yes, but I think curved cauls were around long before the "bow clamp" existed.

[Joe Wood]

Oh I understand now, you need an opposing curved caul underneath?

[Jared Sankovich]

Oh I understand now, you need an opposing curved caul underneath?
Yes.
In my experience, unless you have a significantly thicker (in cross section) bottom caul it will bend.

[Mike Henderson]

Is this another version of Bow Clamp?
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The bowclamp has some features that a shop made caul might not have, but the cost is much higher. I made my cauls from kiln dried 2 by 4's which were a couple of dollars each and I was able to get two 4' cauls out of an 8' 2 by 4. So a set of 4' cauls (two cauls) was a bit less than $3 for me - plus some time to make them. Two 4' Bow Clamps are listed (http://bowclamp.com/buy.html) for $95 (plus $20 shipping).

Mike

[Joe Wood]

"In my experience, unless you have a significantly thicker (in cross section) bottom caul it will bend."

Jared don't you want the cauls to bend??

[Brian Henderson]

Yes.
In my experience, unless you have a significantly thicker (in cross section) bottom caul it will bend.

That's kind of the point, isn't it?

[jack duren]

Yes, but I think curved cauls were around long before the "bow clamp" existed.

Really? Tell me more....

[Jared Sankovich]

Really? Tell me more....

Um...ok? Are you saying [non flat] shop made cauls didn't exist before the "bowclamp" or implying that the curve is not necessary because you can just use flat cauls with shims.

[Jared Sankovich]

"In my experience, unless you have a significantly thicker (in cross section) bottom caul it will bend."

Jared don't you want the cauls to bend??

If you have 2 curved cauls yes. I was referring to attempting to only use a curved caul only on one side. The curved caul will cause the flat caul to bend towards the curve caul, Resulting in a non flat plane.

Use 2 flat cauls in opposition, or use 2 curved cauls in opposition.

[Jared Sankovich]

That's kind of the point, isn't it?

Not if you were expecting it to remain flat.

[Joe Wood]

Jack you have a nice shop and those two pics with the wedges gave me some good ideas!

[Prashun Patel]

I've made these several times. I use the jointer to make them per job. In my Murphy's Law shop, the cauls from the last project are never the right length or thickness. So, I just make them from cut offs from the current project - which usually makes them the perfect length and width. I joint the curves on the jointer. I try not to make them longer than 36-48". They're just easier to handle and make when shorter.

They're easy enough to make, and the reader should know that the curve, type of wood, and accuracy is not so critical. I learned the paper test from Mike Henderson, but truth be told, even when they're not perfect, they work well.

[Larry Copas]

If one wants to become a professional juggler start by balancing two cauls, and two clamps on a hectic glue up.

All thread, a better way.

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[jack duren]

Um...ok? Are you saying [non flat] shop made cauls didn't exist before the "bowclamp" or implying that the curve is not necessary because you can just use flat cauls with shims.

Been using a clamp cauls since 83. Only using Bow Clamp as an example because it's a purchase caul.

[Mike Henderson]

If one wants to become a professional juggler start by balancing two cauls, and two clamps on a hectic glue up.

All thread, a better way.



When I'm applying clamps on cauls, I put one clamp on one end of the two cauls, but over the panel - not outside the panel. That allows me to tighten that clamp without regard to the other side.

Then i go to the other side and put a clamp on the two cauls on that side over the panel. Normally, I just tighten that clamp until the cauls are brought in contact with the wood.

No juggling, easy peasy, quick.

But if threaded rod works better for you, go for it.

Mike

[Bill Space]

The threaded rod idea is neat. I like it.

Threaded rod (and some nuts and washers) is a lot cheaper than a ton of clamps. I can see some advantages to using this idea, especially since I am relatively “clamp poor” :)

One could even substitute carriage bolts for the threaded rod and eliminate the rod/nut protrusion on the bottom. Cheap at Tractor Supply.

Bill

[Carl Hill]

I always use culls. Cauls get really messy.:)

[Dan T Jones]

I'm don't know how folks are making their cauls but why not make a template with a arc drawn say 4 ft long that gives the 3/8" per side and use what ever length you need for a given caul. Would that work?
Dan

[Mike Henderson]

I'm don't know how folks are making their cauls but why not make a template with a arc drawn say 4 ft long that gives the 3/8" per side and use what ever length you need for a given caul. Would that work?
Dan

The problem is that different woods bend differently. Even different batches of the same wood bend differently. Doing something like the OP did takes these differences into account.

But as Prashun said earlier, you really don't have to be exact with cauls and they'll still work.

Mike