Saturday, April 30, 2011

Bagging the bottom - a much smoother ride this time.

The rain has lifted and its just on dusk so time to have a crack at laminating the bottom.

I had planned to try to laminate both sides at the same time for this board but I got cold feet and as it turns out it was probably a good move because of the timing. I am using standard hardener rather than slow this time which gave me workable resin for about an hour ( pot life is about 20-25 minutes i.e when mixing larger batches that sit in a pot which the exothermic reaction heats it up and causes it to go off in 20-25 mins - however when you spread it out into a thin layer the workable time extends, in this case to about an hour). I did some extra work to try to get rid of as many air bubbles as possible and it took me 42 mins before the glass was wet out and the vacuum pump was started.

Here's  a few things I did differently this time and overall it was hell of a lot better job this time.

i) I mixed the right amout of resin. Looking back on my notes from last time, for just a little less glass ( 3 x 6 oz layers) I ended up mixing 750gm of resin. However, I now get what the 'resin %' column in the reinforcement data sheet means. It means the amount that the resin represents in the final laminate. It tends to be around 50% which means there should be as much resin as glass. I weighed the glass and it came out at 350gm. Adding some extra for the glass that extends beyond the edge, the bit that stays in the mixing bowl and you can't get out and the excess you use when hand laying up and will subsequently get squeezed out by the vacuum, I ended up mixing 410gms in total including the 5% epoxy pigment that I used for the bottom. This was perfect. Obviously I wasted a shit load of resin in my last attempt (some of which remains stuck to the rocker table surface).
ii) I didn't use the vacuum through-connector for the vacuum hose but instead ran the vacuum hose half way along the length of the table under the vac film. I had suspected that the through connector was a source of leaking last time. This worked well and also  helped keep an air channel open along the board so that lots of areas were communicating via this channel.
iii) I had one long edge of the plastic stuck down prior to starting to wet out the glass. This reduced the time needed to get the vac film stuck down.
iv) I wet out 2 layers at a time instead of doing each layer seperately. This obviously saved time. I won't know whether this has caused more air bubbles to be trapped until I take the board off.
v) I used paper towels on the top of the board instead of breather material. I'll use proper stuff for the top but this was a cheap way to reduce the materials consumed.

So the laminating schedule this time was (from the bottom up):

6 oz eglass 0/90 degrees
4 oz s-glass 0/90 degress
6 oz eglass 45/45 degress ( used 2 overlapping pieces).
3 layers paper towel
rag drapped across the baord and the head of the vac hose to keep everything communicating.

mixed 410gm resing/hardner/pigment and used about 400gm. With excess squeezed off its likely to be close to the 50% resin percent.

Used standard hardener with R180 resin from FGI which gave about an hour working time. Clamped it under 23 inHg because I thought the stiffer board would need more pressure to bend the extra concave. Not so. 23inHG ( 11.5 psi) was more than enough. In fact I think this was a bit too much as it squeezed out a bit more resin then I hoped. So I backed it off to 20 inHg.

Rocker table showing the vac hose ( 12mm garden hose) run half way down the table.

Board drapped with paper towel used as breather/ bleeder material

The board clamped under 23 inHg. Within about 5 mins a lot of resin had wicked away to the edge of the excess glass.

The board is curing away as I type with the pump engaging about every 5 mins and runs for just a few seconds.

Close inspection of the step  from the balsa to the rail shows that the vac film has no problems conforming tho the circa 4mm radius on the filler between the sidewall and the rail.

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