The George Blog – Applying pressure & Comments

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Applying pressure

Talking to a 055 builder on the forum about making the transom from two layers of 9mm ply instead of solid mahogany (see sketch in previous post), got me thinking about the various ways other builders think of to apply pressure to fairly large off-the-job laminations.

Peter, the builder of the new design 152, simply parked the lamination under a vehicle and used a couple of screw jacks between the lamination and the vehicle to apply the necessary pressure. In effect using part of the weight of the vehicle to apply pressure. Now I guess most modern cars don't appreciate having a couple of jacks under their rear end, but the principle holds good.

An open crawl space under a building would work, for example.

What this has produced in our newer designs, and as we add DXF files for ply components to our existing designs, is a change in thinking for laminated curved surfaces that are best laminated off-the-boat, rather than laminated in place to beams, carlings etc.

We alway used to draw up a male template for a curved surface. And it is true that you can reasonably well drape the thin ply layers over such a mould and use tensioning straps (the sort you use as tie-downs on a trailer or roof rack) to apply the necessary pressure.

But for some (but not all) curved surfaces I think you can get a better result more easily in a female mould and apply pressure with probably a single stretcher (a timber bar, say 100 x 50) and a couple of screw jacks under something heavy and solid (tractor, car, building). The single bar pushes the laminates down into the female mould and the result is nice even pressure over the whole lamination.

The upshot of this is that we have started to draw some DXF files for mould components as female rather than male.


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