August 2019 - Demo 3
Working Plywood with Ed Walker
It was surprising to learn that the Egyptians used plywood some 3500 years ago; the Royal Navy used several laminated layers of hand-sawn veneers at the end of the 18th Century; and in 1847 Sweden, Immanuel Nobel (father of Alfred) realised that several layers of wood bonded together was stronger than a single thick layer and subsequently, he invented the rotary lathe to exploit plywood's industrial potential.
Ed went on to describe the types of plywood in increasing price : Softwood made from Cedar, Firs or Spruces; Hardwood from Oak, Beech or Mahogany; Tropical from wood as the name suggests; Aircraft grade incorporating adhesives resistant to heat and humidity (most memorably used in the WW2 De Havilland Mosquito aircraft); Decorative grade made from thin veneers of attractive woods; and Marine grade made from tropical hardwood with few defects and waterproof glue.
It was startling to see how many holes and flaws occurred within the cheaper grades, all requiring copious amounts of superglue and wood dust to stabilize. It seemed as if the better quality plywood grades wouldn't be much more expensive than the Softwood plus all the superglue!
Ed discussed particular aspects to consider when working with plywood :-
►Let your glue have plenty of time to really set before turning, eg overnight;
►Coloured plastics may be used as laminates but roughen the plastic sheets for the superglue to adhere;
►If using a doughnut ring with your chuck, glue an appropriately sized sheet of ply under the ring for a flat & secure contact;
►If using a tail stock, avoid a pointed centre splitting the laminates of the ply by either gluing a sacrificial piece of wood/ply for the pointed centre to engage or else a ring type revolving centre;
►Gouges will blunt quickly but shear scraping works well;
►With plastic as laminates, watch buffing speed as too much heat will soften it;
►Axminster supply resin-impregnated coloured wood veneers.
The September Competition was set for a turned piece(s) comprising at least 50% of a ply component.
September 2019 - Comp