When I lived in London I did a short course in furniture design at Central St. Martin’s College, run by Ben Panayi. As part of that course I produced a design for a lampshade made from polypropylene.
While I was designing my pattern as described in my previous post, I was experimenting with some cheap fabric that I did actually buy from Spotlight as practice material. I wanted to iron out (mind the pun) any problems by sewing some cushion covers with this practice material first before getting the real fabric design custom printed.
There was much to enjoy about making the cushion covers for the couch. Moving on from plywood to work with another material, attempting to sew for the first time since I was in school, sourcing foam and finding a suitable fabric with a pattern that would match the frame. I knew the cushions would make or break the whole piece of furniture. I also wanted to explore the possibilities of digital printing onto fabric.
Plywood has a property that is very useful indeed for ensuring your pieces are rigid: it doesn’t have a preferred grain.
If you wanted an ‘L’-shaped section using solid wood, you would need to fashion two pieces and join them together. With any joint, there is inherent weakness: it’s weaker than if it were a single piece. With plywood of course, you can make this a single piece as it’s a sheet material.
For every piece of furniture or object I have in mind to make using digital fabrication, I spend a lot of time thinking how the components will be assembled together. These components can be other pieces cut out of the same plywood sheet or externally-manufactured items like dowels, hinges, bolts, electrical cords etc.
This is a way I have used to enable one piece to ‘grab’ another without the use of a slot joint, or even a screw, nail, bolt or glue. Using a dovetail bit, a CNC router can mill a groove into plywood in which the gap at the surface is narrower than at the bottom of the groove.
Kerfing is the use of parallel engraving lines that are cut deep enough to allow an otherwise too-thick piece of plywood to become curved. It has been used for a long time in making the curved wooden sides of acoustic guitars, but I thought it could be useful for some chairs I designed.
With the right dimensions, it is possible to design a plywood piece which can only be put into position by bending it. This can be useful in many ways for objects assembled with plywood pieces.
The traditional way you bend plywood is to glue several layers of thin plywood together in a mould. Using steam to soften the wood fibres, the piece is set and dries over time to produce a piece of plywood that has a fixed bent shape. I want to talk about bending of plywood in a much simpler way which fits the central concept of many CNC-related designs: ease of manufacture/assembly. The purpose I want to focus on here is not necessarily for aesthetics (although it can be a nice by-product) but for strength.
The most basic joint is the slot joint, and it’s a staple when designing for CNC cutting. It’s the joint that, in its simple form, just needs just the standard router bit, doesn’t need any other implements like screws or dowels and it’s very easy to assemble.