Paddy King, Woori Yallock, Victoria

Jarrah Dining Chair
1040 h x 450 w x 480mm d

Concept
To build a dining chair that is:
• Modern in concept
• Aesthetically pleasing.
• Comfortable to sit in, for prolonged periods
• Fully utilises the properties of modern high strength adhesives.

Geometry and joint selection
In order to fully utilise the strength of the adhesive, it was essential that the jointing systems were selected to allow high clamping pressures to be applied to the adhesive interface. Hence half lap joints (or variants) were utilised, for the main load carrying areas.
The tapered staves forming the back of the chair were located with hand cut dovetails into the seat.
The final geometry of the chair, minimised the bending loads in the various components and allowed sufficient bond area to be obtained, to provide very low stress levels in the adhesive.
The final contours of the seat and angle and contour of the back, were established after sitting trials by many people of various shapes!

Glues
A number of adhesives were evaluated on both blackwood and jarrah, utilising 200mm cantilever test samples. Both epoxy and polyurethane systems, produced the most consistent results and similar failing strengths. Selleys Durabond polyurethane was, used for all the main structural joints. Araldite Epoxy slow cure was used for the fitting of the back staves, as it gave a longer working time and better slip characteristics.

Structural testing
Whilst calculations showed a large safety factor, for the design. A prototype was also subjected to a static load on the seat of 280kg. A drop test of 100kg (sand filled bag) from a height of 150mm above the seat. No damage was caused by these tests.

Materials
The original blackwood chair exhibited unacceptable timber miss-match when viewed from various angles.
Jarrah provided a much more consistent and predictable appearance from all angles. The colour variation within the batch of jarrah, was utilised to provide a contrast between the seat and the side members. An additional eight chairs, are currently being produced to this design in jarrah.

Joinery
The chair was made from 185 x 43mm KD dressed jarrah, supplied by Matthews Timber. Components were cut on a bandsaw and final shaping was achieved with spokeshaves.

Finish
To bring out the natural colour and characteristics of the timber it was decided to use three coats of Organoil Danish oil. Polished to a 1500 grit finish.
After curing the surfaces were given a light buff.

Photos: Paddy King