Tuesday, February 1, 2011

The materials

So, time to commit some real $$$ and buy the material for the board. Everything I needed I was able to source at FGI and Dion Chemicals in Brookvale in Sydney. Here's the list:

-1/2 sheet of 6mm Klegecell (2.4 x 1.2 m) $100. Enough for 5 board sized pieces which when laminated (2 x 6mm layers) is enough for 2 boards + another board using a combination of foam and some other core material.
-2 litres epoxy resin + slow curing hardener (40 minute pot life) $70
-7m, 6 oz e-glass 900mm wide. This is enough for 3 layers each side including layers with weave running diagonally across the board $6/m
-750ml of Q-cell (from Dion Chemicals as they sold small quantities) for thickening the resin when using it for a filler.
- ABS plastic for rails. 10mm strip 2.5x the length of the board. This can be heated and bent into the shape of the rails.
- stainless steel T-nuts and 12mm screws . these are the nuts that will be glued into the board and the footstraps will bolt onto. 4 cost $8 from Bomond Trading, also in Brookvale. I saw on the Brokite video that they use flange nuts with ABS around them. The stainless T-nuts took a couple of weeks to get hold of because they weren't so common in stainless (mild steel are readily available). The flange nuts are also a dime a dozen and you can get them straight of the shelf as they are commonly available and look like they would do the job just as well.

Other accessories
-Standard Mold Release $26
-Tacky tap (for creating an air tight seal between the vac bag and the mold surface) $15. -Apparently can use window mastic from bunnings.
-Vac bag connector $13
-Vac bag film 1mx 3m $5/m
-A piece of 1.5mx0.9m rip stop nylon from an old kite. This is the peel ply that goes over the top layer of glass and allows excess resin to be wicked away.
-Polyester wading (using in making quilts) from Lincraft. This is used as bleeder/ breather cloth over the top of the peel ply and keeps the space above the board open enough to allow the air to be draw off. $15 3x2m piece.
- old credit card for wetting the glass out with resin
- coffee cups for mixing the resin in

Couple of things worth noting
ABS plastic - I found this a challenge as it is quite expensive $80 for piece about 1.5mx 0.8m ( an offcut from Allplastics here in sydney.) Expensive because you only use a small amount of it 10mm width around the perimeter of the board.

There are alternatives, namely, reinforcing the rails with carbon fibre matting or Kevlar (thin stripes would do) or using resin thickened with Q-cell and pouring it into a channel around the board that would act as a mold (and throw in some chopped fibre to reinforce the resin further). These other methods may end up being cheaper if your only going to build one board as you won't have all the excess plastic if you can't get a small enough off cut. Also, according to some designers, they allow you to do more with rails which some claim to be a very underestimated feature of a board.

Liquid ABS
I used ABS because I had some on hand but I made the mistake of cutting the rail shape directly out of the sheet rather than heating a straight strip and forming it around the edge of the board. This meant I had lots of offcuts left over which I thought meant were just going to be waisted. However, a friend mentioned to me that a friend of his who makes boards in Melbourne swears by using Liquid ABS to pour the rails.

A little googling turned up what Liquid ABS is. Its simply ABS plastic dissolved in acetone. I took the offcuts and cut them up into pill sized pellets and poured in the acetone and within about 20 mins it was like peanut butter and when left out for the acetone to evaporate off it reconstituted in solid ABS plastic what was indistinguishable for the original. Turns out this is a brilliant glue for ABS plastic parts and also also for casting to make ABS parts.

It seems like you could use it as a replacement for epoxy in the poured rails discussed above and I am going to have a go at using it to fill in around the t-nuts that footstrap bolts will screw into as well as the reinforced sections that the fins screws will pass through.

Cost per board

As you can see from above there will be a fair bit of excess material given the minimum quantities you can purchase. In particular the Klegecell, ABS plastic. If you pure calculate it on a per baord basis and ignore the minimum quantities its going to cost around $150 in material for the board. Footstraps and pads are extra.

You can also see that there is real economies of scale with the foam and the resin/hardner also gets much cheaper as you buy larger quantities. Also, starting with 12mm foam and carving it rather than laminating would also be cheaper as 12mm foam is less than 2x the cost of 6mm.

My plan is make at least 3 baords. Two will have 2 layers of 6mm foam and the 3rd will be made from 6mm marine plywood with large panels cut out and replaced with the foam. This one will be a light wind board like the Slingshot Glide.

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