Cauls for panel gluing ?

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Forum topic by MrWoody posted 06-10-2008 05:37 PM 9456 views 0 times favorited 17 replies Add to Favorites Watch
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325 posts in 3948 days

06-10-2008 05:37 PM

Topic tags/keywords: question gluing panels cauls

I borrowed some cauls for gluing up some panels and they work but I think they could work better.
There is no crown on top or bottom piece. I think they should have a slight crown on one of the pieces.
How much crown on say 30” cauls ? How do you create it ? Would several coats of poly be enough to stop glue from sticking to them ?

-- If we learn from our mistakes, I'm getting a fantastic education.

17 replies so far

View CharlieM1958's profile


16278 posts in 4392 days

#1 posted 06-10-2008 05:44 PM

This may be a very low-tech response, but I use whatever scraps I happen to have laying around when I need cauls to glue up a panel.

As far as the glue issue, I just put a folded piece of waxed paper between panel and caul.

-- Charlie M. "Woodworking - patience = firewood"

View Scott Bryan's profile

Scott Bryan

27250 posts in 3996 days

#2 posted 06-10-2008 06:45 PM

Here is a response for a similar question that Marc Spagnolo sent out today via e-mail:

How To Make Cauls? – Question of the Week

Posted: 09 Jun 2008 07:49 PM CDT

This week’s question comes from Geoff. He writes:
I have a question about cauls and how to make them. I have made some small ones (about 24″) out of some 2x pine. They did the job of gluing up a small table top, but… I want to make a real “set” of them but I don’t know what to make them out of. Could I laminate 1/4″ ply (I have a lot of scrap!) over a curved form to create a slight camber or should they be made out of maple or another hardwood? Thanks for the help and keep up the great work!

And here was my response:

Here’s the great thing about cauls Geoff. They can be made out of just about anything. I have a little bucket that I keep behind my bench that is full of little scraps of wood of all shapes and sizes. But they are really just scraps. Nothing made specifically for that purpose. The only time I specifically make cauls is when there is a very special clamping situation. And usually I use them for that task and wind up losing them a few weeks later.

So I use everything from plywood to solid wood scraps of all species. If you are making a really nice set, you probably can’t go wrong with oak or maple. Poplar would be a fine choice too, as would plywood (if done correctly). If you make a cambered caul out of 1/4″ ply, like you mentioned, you’ll need quite a few strips before the sandwich is sufficiently resistant to bending. You want enough resistance so that the crown of the camber provides the appropriate amount of pressure. You might have more luck using solid wood, but the ply is certainly worth a shot.

  • For those who don’t know, a cambered caul is simply a caul that has a curve in it. These are most useful when clamping long surfaces where you can’t get clamping pressure in the middle of the joint. The best example I can think of is clamping a bookshelf into a dado in the side of the case. The crown of the cambered caul goes on the center of the joint and the ends get clamped down. This applies the needed pressure all the way across the joint. The trick, is figuring out how much of a curve to put into the caul in the first place.

-- Challenges are what make life interesting; overcoming them is what makes life meaningful- Joshua Marine

View Bigbuck's profile


1347 posts in 3837 days

#3 posted 06-10-2008 07:21 PM

I put a few coats of polly on mine and then a put a stip of painters tape on the faces that come into contact with the panel. So far this seems to work pretty good.

-- Glenn, New Mexico

View MrWoody's profile


325 posts in 3948 days

#4 posted 06-10-2008 08:11 PM

Charlie, Scott, (Marc), I would ususally use scraps, but I quite honestly don’t have any scraps here suitable to use. That is why I had to borrow some. :^)
The last few projects have been toys, therefore, scraps gone.
I decided that if I had to buy wood to make cauls, I may as well do it right. That way I won’t get caught without, again.
I think as far as crown goes, I’ll try 1/16th each end from centre.
Thank you all for your replies.

-- If we learn from our mistakes, I'm getting a fantastic education.

View VTWoody's profile


95 posts in 4231 days

#5 posted 06-10-2008 09:30 PM

Clear packing tape is a good solution to keeping the glue from sticking.

View Al Killian's profile

Al Killian

273 posts in 3927 days

#6 posted 06-10-2008 10:38 PM

I have some cuals that I bought and the work great. A fellow woodworker on a different forum makes them. Here is the link to his site I have used them for pressing veneer on to a dresser and had exellent resulsts.

For keeping the glue from sticking use wax paper.

-- Owner of custom millwork shop

View GaryK's profile


10262 posts in 4162 days

#7 posted 06-11-2008 12:46 AM

I just do like Charlie.

-- Gary - Never pass up the opportunity to make a mistake look like you planned it that way - Tyler, TX

View Doug S.'s profile

Doug S.

295 posts in 3882 days

#8 posted 06-11-2008 03:15 AM

Another vote for the BowClamp cauls. They work great.

-- Use the fence Luke

View bbqking's profile


328 posts in 3897 days

#9 posted 06-11-2008 10:24 AM

I have a set of cauls that came from Charlie & Gary’s place. Keep an eye out and when you have a number of similar sized dropoffs from good, thick, ripped stock that will hold up to clamping tabletops & etc., Keep them and use them for that. More than several times I’ve had customers ask what those “boards” are for under my glueup table. I’ve had some of them for years. bbqKing

-- bbqKing, Lawrenceville

View beaudex's profile


65 posts in 3812 days

#10 posted 06-12-2008 08:52 PM

I must admit I use cauls routinely, mine are about 30 inches long and are crowned to about 1/16” on either end. They are made from 2×2 maple stock that I got at the sawmill as junk wood. When I first started using them I never thought that squaring them perfectly would critical however after a few uses I found out that taking the time to square them up made a huge difference. As far as glue goes the packing tape sounds like a great idea. I happen to have a doctor friend who gets me rolls of the table paper they use on the examining table that I use for my glue ups.

-- Derek Tay, Venerate the Tree Design

View Jim Crockett (USN Retired)'s profile

Jim Crockett (USN Retired)

852 posts in 3907 days

#11 posted 06-14-2008 03:45 AM

A question on cauls – I see many references to cambered cauls but don’t have a bandsaw so can’t figure out how to make them. I sometimes use a thin shim in the middle of the length of the caul – doesn’t this serve the same purpose as the cambered caul?

-- A veteran is someone who, at one point in his/her life, wrote a blank check made payable to "The United States of America," for an amount of "up to and including his/her life".

View beaudex's profile


65 posts in 3812 days

#12 posted 06-17-2008 04:51 PM


I just hand planed my caul’s to camber them.


-- Derek Tay, Venerate the Tree Design

View JohnL's profile


33 posts in 3042 days

#13 posted 08-03-2010 11:42 PM

Updating a 2 year old thread…

Found this and it seems to answer the shop made side of things for cambered cauls very well.

-- I'm looking forward to regretting this.

View steliart's profile


2822 posts in 2862 days

#14 posted 01-17-2011 11:48 PM

OK. Even though this thread is a bid old I will update it with my info on how I do my bow cauls.

I use 3 sizes 60cm (30”) – 90cm (36”) and 120cm (47”)

The lumber I use is kiln dried Swedish Pine with straight grain 2×2s or 2×4s
I make sure that at least the opposite edge to the crowned is made flat on your jointer.

The crowned at the ends varies according to the length of the cauls.
For the 60cm I give a 5mm crowned on both ends.
For the 90cm I give a 7mm crowned on both ends.
For the 120cm I give a 9mm crowned on both ends.

First I will get a 6mm (1/4”) MDF and cut it in size… 60×5cm (30×2”) or 90×5cm (36×2”) or 120×5cm (47×2”) and by using a bending stick or something else I will draw my curve according to which template I am doing, 5mm crowned for the 60cm, 7mm for the 90cm and 9mm for the 120cm.
Then I will cut close to the line on my band saw and sand it up to the line creating a smooth even curve.

Use this template with carpenters tape and stick it o your lumber and using a flash trim bit on your router create your smooth even curve. Then on my router table I groove (dado) in the center of straight opposite site of the crowned cauls wide enough to fit my F shape clamps. You can also do this groove with a stack dado blade on your table saw.

And there you have it… Bow cauls for any application

Oh yea. Drill a hole at one end and tie a loop so you can hang them from the wall.


-- Stelios L.A. Stavrinides: - I am not so rich to buy cheap tools, but... necessity is the mother of inventions !!!

View TomBrooklyn's profile


3 posts in 1980 days

#15 posted 06-16-2013 09:05 AM

@JohnL and Steliart: Since the use of cauls is thousands of year old, this thread is still relatively new.

@Doug S. and the person he alludes to: BowClamps are awesome, but expensive. Down the road, I’ll see if I can calculate the exact theoretical curvature required to make a caul have equal pressure along it’s entire length of some common wood types, and post it here.

@bigbuck: using poly and painters tape is like wearing a belt and suspenders.

@beaudex: There is no requirement to incriminate yourself.

@Jim Crockett (USN Retired): Using a shim will leave a gap next to the shim. The longer the caul, the thicker the shim that will be required, and thus the bigger this gap. Mighten it be better to plane or joint a smoother transition from the center of the caul to the end?

@MrWoody: to test your crown amount, you can place some pieces of paper along the length of the caul and something it’s clamped to, and then see how much force it takes to pull the paper out. If you have to, adjust the curve on the caul so it requires approximately equal force to pull each piece of paper out.

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