Wednesday, December 7, 2011

Board #3 comes off the table

After leaving it on the table for 36 hours (its been wet here so I left it in the evacuated environment of the vac table, safely away for the moisture - go the vac pump which run reliably for 36 hours!!!).

Overall I'm pretty happy. Other than the rocker/concave disaster, lots of things I tried worked well.

Sorry about the weird orientation of the images, they got rotated in transit and not sure how to change it.

Peel ply peeled back

Off the table - the footpad reinforcements are visible due to the different density weave of the 4oz s-glass

Eureka!!!!! Look at that shine right of the damn perspex - what a love/hate feeling I've got right now.
The bottom and the graphics looks awesome. There's a lot to be said for getting the amount of resin right and not letting too much get squeezed out.

The top surface was another story. I'm going to need to ask around about this one cause I'm not really sure why it came out with what appears to be too much resin extracted. In the image below you can see the white weave of the fibreglass that is not fully saturated with resin.

Slightly too dry top surface. What the?
Not quite sure what the culprit is here. Some possibilities that come to mind are:

i) The clamping pressure was too high? 27 inHg = c. 90% of a vacuum.
ii) The wood drank up the resin from below and left the voids
iii) The bleeder material is too effective? The paper towels are very absorbent material and so maybe there was excessive 'wicking' up of the resin.
iv) Too little resin in the first place. This didn't seem to be the case when I wet it out but perhaps when the resin got absorbed it was a different story.....

To fill the voids I literally did a 'hot coat' of resin and pushed it into the weave by dabbing it vigorously with a end of a paint brush.

Hot coat, I believe, refers to a polyester resin mix that has a bit of extra catalyst in it so that it goes off quickly. That doesn't work with epoxies but heating the epoxy up sure as hell does. When I was pouring the inserts the other day I put 70 gms of epoxy in the microwave for 15 seconds. It thinned out brilliantly but it went off in about 5 minutes. So I used the same idea here. I heated up 70 gms of resin, put it in the microwave for 10seconds. As soon as it hits the board and the surface area of the resin expands it looses a lot of the heat to the atmosphere so I figured it would be ok to leave it in the pot for 1 minute before I poured it as this would let the reaction that is speeding along due to the elevated temperate progress. It seemed to work ok and after I poured it by about the 15 minute mark it was already very tacky. Given it was slow hardener with a pot life of 35 mins it certainly was a faster process.

I have read, and this is in the category of Trev reckons, that for each 10 degrees you reduce the temperature of the epoxy below the design ambient temperature you slow the curing by a factor of 2. It would seem that raising the temperature by 10 degrees has a more dramatic effect.

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