Wednesday, April 24, 2013

1/12 scale metal folding chair

With a completed music stand, it only seemed fitting to try a folding chair to go with it. I first did one in copper as a proof of concept, manually forming the seat and back and holding the whole thing together with my omnipresent friend, superglue. Even though the legs were not quite right, I was encouraged enough to plunge onward.

I looked at many different chairs on the web and decided on the typical Samsonite chair, one of which I have in the shop which sort of made the decision a no brainer.

The first step was to create a mold for the seat and back. I used tempered hardboard which is apparently what pattern makers use or used to anyhow. The first few attempts resulted in splits at the corners, which I finally attributed to friction when being squashed in the vise. At just about the same time serendipity sent me to Goodwill where lo and behold, a big red Sizzix press. I figure I have gotten way more than my 9 bucks out of it.

With press in hand I went back to deforming duct metal but with a touch of class. The cracking problem was solved with the addition of layers of waxed paper on both sides of the blank.

The original mold I made had a lot of slop and was only aligned via eyeball, sometimes working, sometimes not. I remade the molds with the original carved molds and 1/4 in tempered hardboard with 1/4 inch indexing dowels which also serve to center the blank in the mold. The clearance in the top of the seat mold was much narrowed, and could still be tighter but that is a project for another day.

Aluminum solder is scarce and iffy, spot welding is not suitable for this thickness so I fall back on my friend, super glue, which as it turns out bonds aluminum very well.

With seat and back pressed, legs were bent/built, seat back and braces attached, and the adventure of putting it together commenced. I solved the seat to leg hinge point problem with transverse tubing under the seat, and pinning the leg with a pin thru the seat into the transverse bar where it is held with superglue. There is a photo of the workaround for the seat mount.

It appears that there is a good deal of geometry involved in locating the hinge points for the leg to seat mount as well as where the side diagonal braces go. When attached at the angle the scaled measurements dictated, the seat would not fold completely. Resetting the bracket mount with the seat folded allowed the chair to unfold with the bracket angle less than full size. I can live with that.

I found the color I needed at the hobby shop, and sprayed it. After light sanding with 1000 to 3000 grit it had the shine and bare spots I wanted. Fimo gave me feet and the bumper on the back leg top, (one is missing like most full size).

Another chair happened shortly after that, slightly different shade of the same color, air brushed on instead of rattle can, and bagged parts for another half dozen sit on the workbench for later.

There was a vague tickle in my head that this might be the beginning of a music lesson waiting for the students roombox, which leads to the next entry.



This is a static copper version I did for proof of concept.  It is just copper sheet and wire superglued in the shape of a folding chair.  The leg length and orientation are less than accurate, but it solidified the concept to the point of creating functionality in the ones to follow.

The first chair back was cut and formed by hand as in the following series.  Subsequent backs were stamped out in the press.

Bending the bottom lip of back of chair.

Shaping the ends of the leg braces to fit the inside of the leg tubing.

This is the workaround I came up with to mount the legs to the seat.  Scale would have the legs riveted directly to the seat, a difficult feat at this scale.  I decided to try cross tubes under the seat to provide a gluing area for the pivot pins holding the legs to the seat.  It worked remarkably well, and I recall at some point seeing a chair with similar tubing so I can get away with the addition.

Revamped molds with index pins on the big Sizzix press.

Revamped back mold.

Revamped seat mold.