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Hi Guys
The 2mm card for the X900 arrived yesterday. As you have probably observed throughout the X200 development, I always carry out material tests when I am dealing with something new. In this case it proved to be decisive for the construction of the X900.
The card is 2mm ok - but consists of two layers of 1mm card pressed together. This is called "Bookbinders Card" here in Denmark. It is the cheapest one can buy. Its construction means though that glueing parts together by angle bracket will not work. That is because the glue will only hold the angle bracket to one side of the card while the other is free to break loose, which it does very easily.
Secondly. Bending this card is impossible without damaging it. The fibres are too loose knitted. Bending in large radius bends (above about 6mm radius) is possible without damage so the card can be twisted to match a hull shape if necessary. The X900 is built with my SLO (Straight Line Only) technique, so the ability of the 2mm card to twist is not an issue at all. It does mean however that angle brackets used to hold the structure together cannot be made from the same card.
Because of the loose fibre structure of the card I am reasonably confident that it will be able to absorb a good deal of the plasticising material. It will obviously have to be added on both sides of the card if the X900 is to be waterproof both internally and externally. This is not an option as the weight of the polyester or similar is large compared to the card. And the polyester will cost a couple of times more than the card.
I also performed punching, drilling and cutting with a standard hobby knife tests which showed that the looseness of the structure does not permit fancy operations like that to be performed upon it without resulting in raggy edges.
Sandpaper tests showed that if a very light hand is used and a medium grain sandpaper then good results can be achieved. So on that score the card passed the test.
Pop rivets are not an option. The pop rivets work ok, but the drilling or stamping operations needed to make the holes for the pop rivets damage the card.
Stapling using 6mm x 14mm staples proved to be a very valid solution. The card is not deformed or crushed by stapling.
The results of these tests show that the X900 should be (and therefore will be) constructed as follows:-
1) All major parts - bulkheads and plates - cut from 2mm card.Only flats. No bends or tabs.
2) No glue to be used unless unavoidable.
3) All Angle Brackets cut from 0.65mm card.
4) All connections between parts and angle brackets are by staples alone. The reverse side of the staples will have to be flattened as they are normally rounded by the staple machine.This may prove to be a problem when attaching the hull skin but a solution to that must be found.
5) Only surfaces exposed directly to water will be coated by polyester. Other surfaces can be protected adequately by normal acrylic paint.
6) Special fittings will be needed to attach the hull deck hatches to the frame as these hatches have to be removeable. The fittings will have to allow the use of 3-4mm machine screws. Self-cutting screws are to be avoided as they will eventually gouge the screw hole and prevent making the hatch cover watertight.
So that's it. I am changing the design to accomodate these requirements. There will be no huge changes unless you know where to look, but since only I have seen the original drawings this will not cause any confusion. Although the change to staples complicates things (some parts are not easy to reach with a standard staple machine - I may have to construct a special one for this) - work is saved in that I do not need to stamp or drill the dozens of holes needed for pop rivets, and I can save some money since the staples are much cheaper than pop rivets.
Gerry
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