Furniture Design final project

This term I took a class on furniture design (4.296). Basically, the goal was to learn some woodworking, then design and build a piece of furniture. I chose to make a chair. This project is also a classical example of something I forget to document until the very end, sorry :/

It started with a copper model of my idea. I knew I wanted to do something with curves so I would have an excuse to use steam bending.

copper idea sketch

You can see that the whole chair basically consists of only 2 unique forms – the leg arches and the seat halves.

Quick summary of steam bending:

Wood fibres can be softened when they are wet and heated, but they can’t be softened that much and steam takes a long time to penetrate wood. So lumber is cut into thin slats (~1/8″ thick) and put in a big box fed with steam by a vat of boiling water. The final dimension of my glued together bent part was 1″ thick and 2″ wide. This was made by bending 6 2″ wide slats that were roughly 0.16″ thick.

After 45min to an hour, the wood is soft enough to bend around a form. In general this only works for forms curved in one dimension – more than one dimension is doomed to fail, wood just isn’t built for that. Clear grain should be used to ensure nothing cracks.

Lots of clamps are necessary to clamp the stack of slats onto the form, as the wood will still want to spring straight with substantial force. Many clamps also ensures the pieces conform well to the mold. Start with one clamp in roughly the middle, and work outward from that. After about a day, the wood will retain ~70% of the mold curvature, this is enough for gluing.

Butcher’s wax is applied to the same mold used for bending the steamed pieces to prevent gluing the part to the mold. Glue is applied between each layer and clamped thoroughly. Each clamp is basically touching the ones next to it. Be very careful to tighten from a center point out, otherwise kinks will develop between the layers.

hmm, then I missed about 2 months of documentation. Next we see that the parts have been bent, glued, joined, planed, routered where needed, and sanded.

seat assembly. There was a fancy router jig involved in mitering the ends so that they would meet at an angle.

front leg assembly

Now, one of the main complications with this assembly was that although the front legs could be bolted on with normal carriage bolts, the back bolts had to clamp between surfaces that were angled to one another. So I made carriage bolts with angled heads. Its nice to have custom hardware anyway.

I estimated the angle and made a jig to machine the heads.

angle block with head holding jig

machining the angled hole

(L to R) finished head (front leg, straight), un-drilled head, angled head (rear leg)

ready for welding

straight head, clamped for tag weld, TIG. Also, material = stainless steel

red hot!

The angled bolts were trickier to hold for welding. I turned down the ends of the threaded rod to give a flat surface to rest on the milled hole. The I just positioned the two pieces between two heavy pieces of metal.

welding angled bolt

I cleaned up the welds with some minor grinding, and sanded the head on one of those grinder wheels that feels like scotch brite.

finished bolts with polished heads

At some point I made some filler blocks to go between the seat pieces and the legs. These pieces are cherry, the rest is ash (ash is really nice for bending).

assembled chair

another view

yea, so a bit of sacrifice of comfort for aesthetics. Its not as bad as it looks, though.

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