Chair Prototyping

On the 21/9 I spent the day working on a basic prototype of my chair with the assistance of Bernie from the Workshop. My aim was to determine the right method, materials and machinery for the manufacture of my chair. We began by removing the plastic shell off the chair and sourcing appropriate steel rods for the frame and shell of the chair. Using coat hanger wire we moulded various profiles of the chairs shell to use as a guide. Using the jig we began hand bending the steel, this process was easy and not physically arduous, however, we discovered using tubular steel would be swifter and make for a lighter frame. Next we arc welded two parallel steel rods to the side profiles to form our seat shell frame. Arc welding is moderately difficult but ensures strong bondage of joins. Our next step was placing the frame on the base to determine how it was to be fixed and also how the inner steel rods that form the seat would be joined. We realised the seat needs to have a degree of flex to be comfortable to seat in which requires rods of a certain diameter and length of span. The seat should also not have a base that interferes with its sagging in weight, hence, our decision to remove the three steel braces off the base with a power saw. What remains to be resolved is how to suspend/fix the rods to the frame and how much flex should be allowed? I have ordered in 6-8 meters of 6mm mild steel rod to test this aspect of my chair design.

Hand bent and welded solid steel frame on existing sled base

Clamps used to hold frame in position while welding temporary legs

Jig used to bend steel rod for frame. A hammer was then used to straighten the rod.

Quick welding job to form an outer frame for the shell of the chair. Tubular steel is proposed for the final prototype.

Basic steel section/profile. To be reused as a guide.

Bernie cutting off the base bracing using an angle grinder. 

Three Concepts

Thumbnail Sketches

I started my sketch design phase by drawing the purchased chair and noting all its positive redeemable features as well as its flaws. This helped me distinguish what aspects needed improving, rejecting and reinterpretation in the re-design. I then started drawing any curves evident in the purchased chair exploring how they could inform features of the new design ie. arm rests, curved legs and backrest. Considering the base was in good condition i decided to leave it as is and focus on the 'curve' feature for the shell of the chair. By tracing the existing profile of the chair with bent tubular steel i am reinterpreting the original style of the chair and utilising feasible workshop technology. I finally deliberated on three concepts;

1. Bent tubular steel frame with bent steel rod slats on original sled base

2. Bent tubular steel frame with timber inserts for seat and backrest on orignal sled base

3. Bent tubular steel frame with timber seat and backrest featuring pattern cut-out on original sled base

Quick hand sketches showing conceptual design development. 

Chair Exemplars

Examples of precedent that have direct and indirect correlations with my purchased chair, namely materials and stylistic features. I am particularly inspired by the pattern cut out evident in Nanna Ditzel's Trinidad chair 1993 (botton, far left) as it evokes a sense of fluidity similar to the stacking fins of my purchased chair. Secondly, the Tango chair 1997 by Sigurdur Gustavsson (bottom, middle) has motivated my technological feasible plan to combine timber with powdercoated tubular steel. The steel, in this case, enabling the 'curvy' feature all so evident in my chosen chair.

Written Statement of Purchased Chair

I purchased my chair from The Mission store on Chapel Street, Prahran for a mere $5. What attracted me to the chair was its distinctive stylistic features especially the exaggerated curved backrest and stacking fins. Featuring an injected moulded polypropylene shell and tubular steel frame the chair is believed to be a stackable dining or event chair suitable for outdoor use. While the exact manufacturer remains unknown the manufacturing process of injected moulding using polypropylene has a long history emanating in the 50's and 60's as a solution for a low cost, mass-produced chair that utilised minimal materials and was affordable to all. The manufacturing process involves thermoplastic materials being fed into a heated barrel, mixed and placed into a moulded cavity where it is left to cool, harden and assume the configuration of the mould cavity. Polypropylene is strong, heat, fatigue and impact resistant, easy to clean, weatherproof and can be joined by heat fusion rather than harmful glues. The bent tubular steel sled base on the other hand uses a technique first developed by Marcel Breuer in 1925. The material was available in quantity, technologically feasible and could be mass-produced. In the purchased chair the steel functions as a solid support for the plastic that allows a degree of flex and is supported by pressed steel braces and a middle steel rod to prevent hyper extension of the legs and it supports even weight distribution.