Saturday, March 10, 2012

B6 'Mini-Me' under the pump

Started putting the next board together last night.


I previously poured the inserts and left the core in 4 pieces to help put the concave in it without having to fight against the stiffness of a single piece core.

In the B5-Light Wind board I used 50mm strips of 6mm core and this worked well. I left these as 100mm widths just to see if it still preserved the concave as it did previously.

The set up this time is

4oz e-glass pre-cured topsheet with encapsulated graphics printed on tissue paper
450 gm stitched e-glass ( this stuff is a pleasure to work with)
2x 65mm uni-directional carbon stips the full length of the board including over the tips
8mm paulownia wood core thinning to 4.5mm at the rails
4.5mm ABS plastic rails abraded but not heat treated.
2x 65mm uni-carbon strips
450 gm stitched e-glass
160 gm e-glass
pre-cured 'gel coat' of epoxy with white pigment (left to sure for 2 hours before dong rest of lay-up)



'gel coat' of epoxy - c. 200gm.

Although its not recommended on the forums due to chance of explosion, I heated the 'gel coat' resin in the microwave for 30 seconds and then let it stand for about 1 minute so that it would start to thicken before I applied it to the surface. The reason is that the FGI resin thin enough that it pools on the perspex rocker table top. Letting it thicken, paint it on and then paint over any holes that opened up in the coat ( this happened for about 10 mins) allowed me to get a full coverage on the perspex.

The kit of bits
Under the pump
Then I just assembled it all and put in under a vacuum.

I used 200 gm resin for the bottom 'gel coat'
450 gm resin for the 160gm and 450 gm glass on underside and for gluing the core and rails in place.
50gm of resin to make filler with q-cell to put around the area where the two decks joined as I wasn't sure whether the top sheet would bridge over this join so I wanted to make sure there was something there to fill the void
300 gm of resin for final 450gm stitched glass.

So it was a fairly resin rich layup this time. A reasonable amount should be squeezed out but I wanted to saturate things because I wanted the resin to push into the joins between and around the core pieces.

I layed the whole thing up flat and then put it into the bag and evacuated it before moving it to the table. This turned out to cause a problem with the top sheet. I took the pressure to about 20 inHG (2/3 atmos) and when I then clamped the board into the rocker table the topsheet buckled, presumable because it was clamped too tightly for it to slide over the rest of the layup. I think that the area under the buckled area should be filed with resin because it was pretty well sealed so there was no way air could get sucked in. Only time will tell. If it has an air void then this is where the baord will fail.

Its been under the pump for about 12 hours now and I'll going to leave it for 24 before I take it off.

It was a slow layup this time at 1 hr 45 mins but it was a cool night so the resin was still workable. However, the process of assembling it as a kit doesn't seem to have improved the process greatly in my set up because the hidden time sink is designing the templates and moulds etc to deal with the poor tolerances that I can achieve in my set up while the pieces fo 'tools' still functioning as intended. For example, the mould piece that clamps the rails to the core and holds the core together from the sides needs to accommodate rails of slightly varying thickness and moulded rail pieces that don't quite conform to the outline of the core. This means endless tweeking in situ which is time since. I think that v. tight tolerances are key to making this approach a net benefit.

Also, the reusable vac bag hasn't proven to be a great success either.  I've used vynl table protector (1mm thick) and despite the apparent strength of it it is relatively easy to puncture and so I have had a real stuggle to maintain a good seal on it. This is another tick for pnumatic presses. I have been thinking about possibility of pouring concrete moulds........


Time to do some rethinking.......

3 comments :

  1. I had a very close look at some new boards over the weekend and i have to say i expected more in the quality stakes. Most had the glass weave pattern showing and some actually had a patterned bottom.

    Makes me think why try for the elusive perfect shine when the big boys don't?

    I know you're trying to make it simple , but it looks like you have moved from simple to being harder to make it all work right for yourself. As it gets more technical it's getting more frustrating and time consuming.

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    Replies
    1. Hey Peter,

      Your right that the attempts to simplify have overall increased the complexity. The approach is very similar to the way Brokites do thiers but I now realise there is one major difference that I didn't even consider before. They use foam cores which are able to be compressed at the edges where they join the rails and in the inserts so that small size variations can be overcome by squeezing it tight. Wood cores do not forgive variations and small size variations mean gaps. The other big time issue is using proper top and bottom sheet material that then avoids all the pre-curing and the gel-coat and waiting etc.

      I was thinking that the ability to create a kite of pieces would mean that I could create all the pieces in batch processes and building the board would just be a matter of assembling the bits as needed. For an scale bigger than 1 at a time this would be a good benefit.

      Time to rethink the goals while making sure its still a fun process..

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  2. I think you hit it on the head right at the end there "fun" if it aint then it isnt worth doing.
    I hear you about the pvc table sheet being to easy to damage. I did see thinker stuff at bunnings that if heated slightly would conform nicely and still give a good shine. If i didnt spend my weekend at the state titles watching i would have tried it.

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