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Minimum-Affordance Side Chair

Author:admin | Visited- | Date-2010-4-24

Minimum-Affordance Side Chair

Minimum-Affordance Side Chair 

Chairs are difficult to build when compared to other furniture. Nomadic Furniture, a book otherwise replete with good, simple plans for quality do-it-yourself furniture, equivocates on the issue of chairs: "We think that 'dining' chairs, which also work as desk chairs, can be bought cheaply enough...so that you should not try to build one." (p.11) Although the book and its sequal do include several more-or-less successful plans for chairs, these are all of the "lounge" variety, and would serve poorly as dining chairs. Lounges are not expected to be as mobile as dining chairs; they can be difficult to move and still serve their function adequately, and easing the weight constraints thusly makes things much easier for the DIY designer. A dining or "side" chair, however, is expected to be readily pushed out, or pushed in, or shuffled around to accomodate guests.

The original concept sketch for the MASC design.

As may be obvious to my readers, my design insticts tend toward minimalism. Tasked to appoint a dining room, my first answer is "Make a low table and sit on the floor." If a table of normal height were required, I'd say "Provide it with stools." If stools were also unacceptable, for whatever reason, I guess I'd admit the need of chairs. In this circumstance, the question becomes "What is the minimal object that constitutes a chair?" The MASC is my answer.

The MASC alongside the great Emeco 'Navy' side chair.

Of course, when we begin to talk about "minimizing" our designs, we are immediately obliged to qualify our answers in terms of which of the many design variables we are concerned with. There are, obviously, at least as many "minimum" chairs as there are nameable qualities of chairs. Here are a few others:

A cost-minimized plastic chair.  $3.69 apiece. The weight-minimized carbon fiber 'Light light' by Alberto Meda weighs less than 1 kg. The manufacturing-minimized 'Sof sof' chair by Enzo Mari.

The MASC is a minimum chair in two senses. First, it has the minimum number of "affordances" (Donald Norman's term) to be called a chair. What's the difference between a chair and a stool? Well, a chair has a back support of some type, while a stool does not. In a chair, the back support also serves as a "handle" whereby the chair may be lifted and moved without bending over, as is required for moving a stool. So I began with the minimum stool (in terms of rarity), which is an inverted bucket, and added a minimal back support. The back support was designed to be manufactured and attached using minimally-expensive and minimally-rare materials: It is comprised of an approximately 8' length of 3/4" galvanized EMT conduit, 6 one-armed conduit straps, two sheet metal screws, and 6 sets of nuts, bolts, and washers. All parts of the chair are galvanized steel, providing visual and aesthetic unity.

Detail showing attachment of bent-conduit back support to bucket.

Secondly, the chair was designed to require minimal effort in its manufacture. The construction is accessible to anyone with access to an average hardware store and basic hand-tools. Besides a drill and a selection of screwdrivers and wrenches, the only "exotic" tool required is a manual conduit-bender, as shown below, which allows the EMT to be bent smoothly without crimping.

The head of a manual conduit bender, which is generally sold seperately from the handle.  Make sure you get the bender head for 3/4-inch conduit. The complete conduit bender, with handle attached.  The bender head I purchased accepted a threaded length of 3/4-inch galvanized pipe (NOT conduit) as a handle.

Construction details are as follows: A 10-gallon garbage pail (Dover Parkersburg Item No. 910), a 10' length of 3/4" electrical conduit, 6 3/4" one-armed conduit straps, 6 1/4-20 by 1/2" hex bolts, 6 1/4-20 hex nuts, 6 flat washers, 6 lock washers, and 2 1.5" sheet-metal screws were procured at the local hardware store. The lid of the pail is not required. All labels and stickers were removed with Goo-Gone (TM), and the handle and handle brackets of the pail were removed by drilling out the rivets in each handle bracket with a 1/4" drill bit.

4 holes in one side of the pail where the rivets holding the handle-brackets in place were drilled out.

The conduit was bent at a point approximately halfway along its length to an angle slightly greater than the 90-degree capacity of the conduit bender (note resultant crimping, below), forming one half of the "hairpin bend" that makes up the seat back in the finished chair. The conduit was then reversed in the bender and the second half of the hairpin bend completed, taking care to position the bender as close as the design of the bending head would allow to the first bend, and to match the angle of the first bend as closely as possible. The "legs" of the hairpin, which were then crossed due to the acute angle of the first two bends, were bent outward at a point approximately 14" from their termini, so that they no longer crossed, but rather ran parallel about 3" center-to-center. Lastly, the two legs were bent back at an angle of about 20 degrees each, forming the angle of the seat-back with respect to the seat itself.

Detail of one of two small 'crimps' in the seat back caused by pressing the bender past its nominal 90-degree maximum bend.

The completed seat back was attached to the inverted bucket by clipping the conduit straps onto the bent conduit in appropriate places, and then holding the assembly in place and marking the location of the holes in the conduit straps on the surface of the bucket. Holes were drilled and the assembly attached to the bucket one strap at a time, being careful to check the alignment of the entire assembly before each one. Flat washers, lock washers, and nuts were installed on the interior surface of the bucket, with only finger-tightening during the hole-drilling process and wrench-tightening once the entire assembly was in place. Lastly, two long holes were drilled in the uppermost conduit straps, through the conduit itself, and into the surface of the bucket to acccomodate the two 1.5" sheet-metal screws, which were installed to prevent torsional and longitudinal slipping of the strapped-on conduit.

Interior of the bucket showing attachment of 6 conduit straps, plus anti-slip sheet metal screws. 

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