This afternoon I did a trial run for making the deck beams.
I cut the test jig from an old kitchen work top. Firstly, I used the hand jigsaw to form a curve representing the upper side of the laminated beam; then I made an identical piece which I screwed to the first, so that it was 45 millimetres equidistant below it. The lower curve represented the bottom of the beam, and 45 millimetres below it I drew another identical curve and trimmed both pieces to match.
There was my jig ready for laminating the trial piece of deck beam, but before applying epoxy resin to the plywood strips, I first taped thin plastic sheeting to the jig to prevent epoxy from coming into contact with it. After using a brush to apply slightly thickened epoxy to both sides of the 4 by 24 millimetre plywood strips, except the upper side of the top batten and the lower side of the lower batten, I bent them around the jig and held them in place with clamps. I took the precaution of placing plastic covered pads between the clamp heads and the upper side of the beam to make sure they would not be bonded together by spilled epoxy.
Tomorrow, when the epoxy will have hardened, I shall remove the test deck beam from the jig and use a rotary grinder to smooth away any nodules of resin that may have squeezed out while the beam was under pressure from the clamps. Then I’ll use an electric sander and a sanding block to make all surfaces smooth.
In all, I used 11 strips of 4 millimetre plywood to build up the vertical thickness of the beam to 45 millimetres; the thickness of the epoxy accounted for the extra millimetre.
There will be lessons learned from the exercise - already I have discovered that when I cut strips from plywood I should allow at least a millimetre between them to compensate for the thickness of the jigsaw blade.