Custom cauls for gluing up curves
Words and photos: Darren Oates
The key to a successful glue-up for me is an effective glue-up caul design. All my furniture involves curved elements, with these either being fixed to a flat piece or to another curved piece. Over the years I have designed cauls that will ensure seamless and strong joins (photo 1).
I have cauls for use on unfinished timber that are designed not to slip, and sets that are used on fully finished timber and therefore designed not to mar the surface.
My Omega hall table is shown above in photo 2...
...and the cauls used to glue its steambent tapered legs to the cross member prior to finishing are shown above in photo 3. These cauls are made from bending plywood, MDF, solid timber and 120 grit sanding belt.
They are shown in use here in photo 4.
Photo 5 shows a closer view of the Omega caul, and above it, another caul that I use on my Parenthesis hall table. On both cauls, sections of a sanding belt are folded around the MDF which is then glued and stapled to the bending ply and the solid timber block. This ensures the sanding belt cannot slip if, say, it were just glued to the caul.
The job of the sanding belt is to help hold the caul in the correct place while under clamping pressure. The timber blocks are angled so the clamp used forms a 90° angle to the surface the curved element is being joined to. This ensures a nice flat seamless join. The Omega table caul suits its much curvier leg which is why I have used both the bending ply and the MDF to form the shape required.
Two cauls are shown in use on my Omega hall table legs in photo 4. You can see how the solid timber blocks, once clamped, are parallel to both the joins and to each other, and work to produce a perfect join. Not shown fully are the three clamps that hold the cauls to the legs. Even though this is a glue-up of unfinished timber I still place blue painters masking tape about 1mm from the glue line to reduce the risk of epoxy squeeze-out going onto the raw timber once the three pieces are tightly clamped together.
The cauls shown in photo 6 are for the final glue-up of one my signature Parabolae hall tables, shown below.
The Parabolae table cauls are designed for use after final coats of lacquer have been applied and are therefore padded with felt. I also wait 48 hours after the final coat has been applied before I undertake this glue-up.
Photos 7 and 8 above show the construction of the cauls used for my Archimedes coffee table that you can see in photo 1. The solid timber blocks are glued and stapled to the 3mm MDF. There is no requirement to run the felt along the entire length, as at this spacing the MDF does not come in contact with the finished timber.
In photo 9 you can see how the angled block is parallel to the flat surface the curved element is being glued to – this is so the camp can provide maximum downward pressure. When pressure is applied evenly to the angled blocks on either side of the MDF strip they prevent each other from slipping and are locked in place.
I’m pretty happy with the results I’m getting. It’s amazing what a well-designed gluing caul can do when joining curved elements. I have about a dozen limited production hall and coffee tables and each has their own specific set of glue-up cauls. You may be able to use one set on another table but this could be a bit of a compromise. When you take into consideration the average amount of time that it takes to make a piece of furniture, the time taken to design and make purpose-built glue-up cauls will be easily repaid after only a few pieces are made.
Darren Oates @darrenoatesfinefurniture is a studio furniture maker in NSW who also teaches at Sturt School of Wood.