# Teach me about wood cauls please



## ponch37300 (Feb 27, 2008)

I have been reading about using cauls in projects and would like to make a pair. From my searching they have a curve to them so they will put equal pressure all the way across the wood. What is the best way to make this curve and what type of radius should this curve be? Hoping to make a couple sets up because I want to make a cutting board and some other projects sometime soon. Thanks


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## Steve Neul (Sep 2, 2011)

Since the cauls you are wanting is to make a flat glue up panel I wouldn't make the cauls curved. I make them straight and cover the edge with clear package sealing tape to keep them from sticking to the glue up.


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## ed_h (Dec 1, 2010)

I just take a pass with a plane from the center to each end, then a few moire progressively shorter ones. The bow probably is around 1/8 inch. You don't notice it unless you sight down the board.

The idea is that when the ends are pulled down flat, there is pressure in the center and all along the caul.


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## ed_h (Dec 1, 2010)

Steve Neul said:


> Since the cauls you are wanting is to make a flat glue up panel I wouldn't make the cauls curved. I make them straight and cover the edge with clear package sealing tape to keep them from sticking to the glue up.


You would normally have a curved caul on both sides so the pressure is balanced and the work stays flat.


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## ponch37300 (Feb 27, 2008)

ed_h said:


> I just take a pass with a plane from the center to each end, then a few moire progressively shorter ones. The bow probably is around 1/8 inch. You don't notice it unless you sight down the board.
> 
> The idea is that when the ends are pulled down flat, there is pressure in the center and all along the caul.


Thanks for the details. Can I do this on the jointer by starting in the middle and keeping pressure on the infeed side? Might sound funny but I have a jointer but not a plane! I actually found 3 planes in my grandmas basement a couple weeks ago but I'm sure they haven't been use for 30-40 years so would need some work getting them usable again with the surface rust and I'm sure the blades need sharpening.


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## Steve Neul (Sep 2, 2011)

ed_h said:


> You would normally have a curved caul on both sides so the pressure is balanced and the work stays flat.


The problem I've had with making the cauls curved is if top or bottom caul was stronger than the other it would make the panel curved. A person really shouldn't need cauls unless glueing up thin material.


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## BassBlaster (Nov 21, 2010)

I personally wouldnt mess with making a curve on a caul for cutting board use. Now, if you are making cauls for large table top glue ups then certainly go through the trouble. My cauls are straight and I havnt had a problem with them. I use to make cutting boards without cauls. Mine are just two 3/4" X 1 1/2" strips of red oak laminated together. That makes eight total strips to make one set of cauls. Finished with poly and covered with packaging tape. They work perfect for cutting boards.


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## rookiewoodworker (Sep 10, 2012)

I just put a piece or 2 of masking tape in the middle of the caul.


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## ed_h (Dec 1, 2010)

Yes--the only reason to put a curve in a caul is to apply pressure to an area where you can't get a clamp (or don't have enough clamps!). 

The build-up method, like with tape, works as well as the stock removal method. 

Yes, I think you could remove stock with a jointer as well as with a plane.


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## Hammer1 (Aug 1, 2010)

Curved cauls would be used in situations like gluing an edge band on a long shelf where you only need or want to use two clamps. The curve distributes the pressure along it's entire length as the clamps are tightened.. When doing flat work, you are better off with straight cauls. Using curved opposing ones is a little like trying to clamp a couple of rocking chair rockers opposite from each other. Even with a very slight crown, when clamping one end you double the size of the crown at the other end. 

As someone else said, one caul may be stronger than the other resulting in a curved surface. Another issue is that the pressure from the curve can indent the wood. In those cases where a curved caul is called for, the crown is dependent on the species, length and width of the caul. I wouldn't curve a 36" long caul but might put a 1/16" crown in a 3/4" x 2 1/2" x 6' one. I wouldn't crown opposing cauls, just single ones when the work calls for it. Essentially, you are trying to create an even controlled bow to the edge, which you aren't going to do with a jointer that cuts straight. If you are doing heavier work, you will want cauls to match the work being done. 

Cauls are one of those trade secrets, so to speak, that help insure that you get flat panels, doors, table tops and adjacent boards aligning with each other. They also reduce the number of clamps you have to use as well as having to clamp on both sides of a panel to prevent pulling a bow in the surface. When using them, you need to either use horses or stand offs on your bench to allow room for the bottom caul and the clamps that will hold them. 

I've collected several left over pieces of red oak from projects, about 3/4" x 2 1/2" x 36". Ran the edges on the jointer and marked them. They get stored on the shelf like any other assembly aid, there when I need them. I use strips of wax paper laid on the work to prevent them getting glued to the work accidentally. I've tried tapes and finishes but with years of use, those methods don't stand up. When I first place the cauls, I lightly tighten the clamps holding them, then use the bar or pipe clamps to pull the boards in the glue up together, lightly at first, then tighten the caul clamps and finally firm up the bar clamps. They will cut your clamp up time in half and end any wrestling you used to have with work pieces and clamping up.


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## ponch37300 (Feb 27, 2008)

Thanks for all the info. Any details on making cauls? Just an oak board or is there more to it?


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## MeasureTwice (Jan 12, 2012)

Check out this article by Highland Hardware


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## cabinetman (Jul 5, 2007)

ponch37300 said:


> Thanks for all the info. Any details on making cauls? Just an oak board or is there more to it?


Cauls can be made from many things. My take on them is more about being preventive rather than corrective. Their use should include a little bit about the whole glue up process. 

I've been a believer that a glue joint, no matter what kind (and edge glue ups are included, IMO, when speaking of joinery), should be well fitted and likely not need a whole lot of pressure. Starting with the boards themselves, edge jointing so their edges are straight, and 90 degrees to their faces. They should be dry fitted for a match checking for gaps. Alternating grain (crowns to the rings) will help in overall stability.

If necessary, I would use fitted splines, and not biscuits. When clamping up the boards, no matter what type of clamps are used, they should alternate (top and bottom) along the entire length. If the clamp ends are positioned more closely to one of the surfaces over the other, it can pull the boards into a curve across the boards, up or down. This can be detected as they are being positioned and being tightened. 

In having a good dry fit, it doesn't take extraneous pressure to bring the boards together. Excess pressure in cross clamping may be due to the boards or a board not being straight. Besides checking for that, its a matter of maintaining their overall alignment of their surfaces to be the same. When I mentioned that cauls to me should be considered preventive than corrective, I mean that the cauls should just be clamped preventing misalignment rather than forcing the boards to move into alignment. Joints that have been glued up under stress are less substantial than those that are well fitted.

I've tried the curved caul method, and there are many variables to the size, length, and proximity of the curve in relation to the length. I've had good luck with just straight cauls, and some weren't even wood. I've got some aluminum window mull bars that are "I" beam shaped, with 1¼" faces top and bottom. They don't bend at all.

As in many shop procedures, along with the dry fit, have handy all the parts and pieces you'll need to do the glue up. You don't want to be running around looking for another clamp, or getting a new bottle of glue, or adjusting a clamp to fit. Time is of essence.










 







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## Dave Paine (May 30, 2012)

Lots of good replies.

I use clamping blocks which can be considered cauls when I do not have clamps with a deep enough throat.

For cutting boards, I do not feel it matters whether the clamping block is curved or flat. My preferred clamping blocks are solid aluminium blocks about 1in x 1 1/4in. Originally sold by Woodpeckers, but now only made for "one-off" orders.

The pieces being joined should ideally have a good fit. The clamp ideally is merely holding the pieces until the glue sets, and should not be forcing a gap closed. Sometimes there will be small gaps, but they should be minimized.

Whatever you use for your clamping blocks should be reasonably wide to distribute the pressure of the clamps to avoid compressing the wood in the board. I use at least 1in wide. 

Another consideration is to prevent the clamping block from sticking to the wood in the board. You should cover the surface of the clamping block with masking tape, and ideally have a piece of plastic between the clamping block and the wood. Something which will not adhere to either side.

You could attach UHMW material to the bottom of the clamping block and then never have to worry about this sticking to the wood in the board.

http://www.woodcraft.com/search2/search.aspx?query=uhmw sheet


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