Monday, June 11, 2012

Curved Bench

8:38 AM Comments 1

Curved Bench

Materials = Sapele Veneer and Sapele Hardwood

We recently had a client in San Francisco contact us about making a shoe bench for one of his clients. The bench needed to be fairly small, since it was going in a foyer shared by three apartments, have the ability to hold a fair number of shoes, and have a striking design.

After creating a few designs that incorporated a box joint detail where the legs and top met, we decided to throw that design out and go with a more streamline and sleek look, where the legs curved into the top. The client loved it! We then added a shelf to hold the shoes off the ground. We made the shelf out of slats, rather than a solid flat surface, which made the bench feel more open and light.

We began the project by building the frame that would give the bent lamination, which is the bench itself, its shape. We made the sides and spacers out of 3/4″ melamine scraps we had laying around the shop.

We have done some bent lamination in the past, but the bent lamination was not structural. With this project, the bend lamination was the entire piece, which meant that it needed to be rock solid and pretty much perfect!

Since using solid wood to form the bench itself was out of the question, I narrowed our field of options down to two contenders, 1/8″ MDF and 1/2″ EconoCore. I chose the EconoCore because the idea of trying to glue 12 layers of the 1/8″ MDF together to reach our desired thickness seemed a bit overwhelming. The EconoCore was more expensive, but with the amount of time it saved in the long run, it was probably the economically wiser choice.

As you can see from the picture above, the EconoCore is a a sheet of 1/8″ Masonite type material with kerfs on one side that create 3/8″x3/8″ ribs. We purchased a 4×8 sheet and cut the three pieces we would need for the bent lamination.

The next step was to glue those three sheets of EconoCore into the shape of the final bench. We decided that a polyurethane glue would be our best option for two reasons. The first was the expanding nature of the polyurethane glue would aid in filling the voids of the EconoCore and help to stiffen the glue-up and minimize any flexing. The second reason was the fact that polyurethane glue is activated by moisture and we needed to soften the EconoCore at the curve to try and alleviate any stress, so now, the water that would activate the glue, would also help to soften the curves.

We sprayed all the mating surfaces with water and liberally applied the polyurethane glue. We used a platen and cauls on the top to help distribute the clamping pressure and should have used platens on the sides, but totally forgot during the craziness that was this glue-up, and instead only used the cauls.

We were a bit nervous about whether or not the laminated EconoCore would be stiff enough to support a persons weight, but once we removed clamps and tested the strength of the assembly by sitting on it, our fears were put to rest. Keep in mind, we still needed to add trim to the front and the back and add a shoe rack to the underside, which would increase the rigidity even more, but even without those pieces, the assembly was strong enout to hold 150lbs without flexing.

We cut the uneven sides and bottoms off using our sliding table saw and then glued on a 1″ thick piece of Sapele to protect the EconoCore.

The blue material you see on the surface is an automotive putty, which we used to level out some of the depressions that were created during the gluing stage as a result of not using a platen on the sides.

With the bottom trim attached, we milled, glued, and clamped on the side trim. We also laid out the placement of the four shoe rack pieces before we adhered the inner sheet of veneer.

Once the glue had dried overnight, we flush trimmed the side trim and, since we chose to use a PSA (pressure sensitive adhesive) backed veneer, we sealed all the surfaces with two coats of sanding sealer to ensure an adequate bond.

Applying the veneer was only moderately difficult. We had to pay close attention as we pressed the veneer down to make sure we did not pull off to much of the backing paper and accidentally stick part of the veneer down that we did not want to. Also, PSA backed veneer bonds by having the veneer “ground” into the substrate using a tool called a veneer hammer. Well, to get adequate pressure, you really put a lot of weight into it, which was quite difficult on the curves.

We trimmed the extra veneer, eased over the edges with some sandpaper, and turned our attention to the shoe racks.

A few steps prior we laid out and drilled all of the dowel holes for the rack pieces. Now we placed the rack pieces into position and continued our holes into those pieces. We inserted some glue and dowels to the holes, added some clamps, and walked away for the rest of the day.

The last difficult step was to veneer the outside of the bench, and it was not even that difficult, since we were only dealing with outside curves, not inside curves.

After the veneer was adhered and the excess was trimmed off, we gave the entire bench a light sanding to remove any pencil marks, rough edges, and water wipe marks, and sprayed on two coats of sanding sealer and one coat of pre-cat lacquer.

The final result is one of my favorite pieces we have ever built!