Monday, 9 June 2008

Step 5 - Assembly part 2

So now the board has cured for 8 hours. Out of the bag it comes and now prep time for the fibreglassing. I have used a 280gm Twill glass cloth for this is it is supposed to have good drape qualities, meaning it confirms to corners and shapes better than other types of glass cloth.

Using my cardboard template I cut the cloth out. I ordered 5 meters of cloth and this was enough to get 5 layers for the board with some to spare. I cut out two layers with the direction of the weave running 0/90°, these are to be my outter most layers - the very top and very bottom skin if you wish. Next where two more layers cut with the weave running 30° and a final layer at -30°(or +60° if you like).

The layers are to be laid up like this

  • 1st layer - 0/90°
  • 2nd layer - positive 30°
  • 3rd layer - negative 30°
  • The core and ABS rails
  • 4th layer - 30°
  • 5th and final layer 0/90°
This layer up should give the board the the strength and flex needed in the correct places.

So with my layers all cut and board prepped for the fibreglass work, I laid everything out starting with my release layer and mixed my resin, I added a white pigment to the mix at 3% by weight to give a nice base colour since I have never worked with fibreglass I used the min suggested ratio for everything.

I laid the first layer (5th from the list above working up to the 1st), on top of the release layer (polyproplene film) and gave it a good coating of resin (this is called wetting out). Now the second layer, then coated the base of the ABS rails and core and place this on top of the 2 layers. Then started to coat the top of core with resin ready for the next layer, but discovered that the resin was starting to string. I noticed that there was a hard flat something in the resin. When I tried to take this out using the vinyl gloves, it was super hot and melted the tips of the gloves. This is where things start to go pear shape and my lack of experience comes in. Epoxy when mixed with a harder always generates heat. Mixed in large quantities this can actually burst into flame. The amount of resin I mixed was to much (900ml in a paint tray) and it was startng to cook and at the same time cure the resin at a fast rate.

I decided to save what I had so yiped off as much resin as I can from the top of the core, cut some more release layer and lay that on top and start the vacuum bag process. This was going to have to be a two stage affair if I was to save the board. So on with the release layer, peel ply (a type of material that resin does not adhere to) then the breather layer and finally the vacuum bag. Seal it all up and connect it to the vacuum pump and wait another 8 hours.

Later that night I took it all out and was impressed with what I achieved. Not only was the board saved but it was smooth on the bottom and everything had bonded nicely. Not bad for my first go at vacuum bagging and fibreglass - my first major fibreglass project with some lessons learnt.

Mixing the resin - to much mixed wetting out the first layer
wetting out the second layer coating the base of the core with resin
lining up the core on the wetted layers
bottom of the board with excess fibreglass trimmed off

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