Wednesday, March 14, 2012

B6 - Mini-me off the table

So finally off the table and cleaned up ready for drilling.

The bottom came out very smooth. Putting down the coat of resin first and letting it cure worked well. No sign of the uneven surface of the core due to the carbon tape. Color came out a bit blotchy. This is the second time I've had the white pigment separate out under pressure and I'm starting to think that the pressure is sufficient to cause the different molecular weight components to separate.

Interesting also to note with the topsheet, pre-cured skin which cured for 24 horus before I put the white fill coat over the back still ended up having the white fill coat diffuse through into parts of the encapsulated graphics. I guess this shows that even though the resin appears to be cured it is still in a fluid state for a long time albeit a very viscous one. The only way I can see to fix this is I continue with the pigment in the resin is to speed up the curing by elevating the temperature for post -cure. the better option would seem to be to use opaque material as backing for the pre-cured skin.

Overall there were a lot of improvements in finished product that I'll carry over into the next one. Two things of note straight away that did work.

i) I layed the board up on a flat table and then bagged in and evacuated it down to c 20 in Hg. This meant that when I bent it into the rocker table the top skin could not slide over core and so it buckled. I noticed this while it was under the vacuum but it was too late by then. The buckling is very obvious in the right light. Fortunately it shouldn't affect it structurally as the potential voids underneath are filled with resin

ii) With an impervious top sheet almost no resin was squeezed out from the top of the board. This was exacerbated by the curves on the top with the surface stepping down from one layer to the next. This seems to have created a resin trap for resin being squeezed out and around the contours there is a noticeable deposits of resin under the topsheet. Also the board turned out heavy as a result of this and the extra resin for the topsheet and the 'gel coat' bottom each of which used around 200 gms of resin. As a result the board came out at 2.7kg without accessories. Well over 500gm heavier that other similar efforts.
Ripples due to 'pre-clamping' the topskin to the core before bending in rocker table. Pink color is courtesy of Picassa!

Do's, Don'ts and Don't Knows to follow.

1 comment :

  1. Great job. Could be that the precured top sheet can really only be used on a lightly curved top rather than one with rebates around it