Saturday, April 30, 2011

Vacuum bagging lessons - the error part

The pump held the vacuum for a good 12 hours and I just unveiled it. 99% good. 1 serious percent bad.

I used paper towels on the surface of the board as breather material on the basis that I was only going to be laminating the bottom and so no need to think about the top. If there was zero excess resin in use underneath then this would have been fine. However, there was a small amount of excess and because the seal to the perspex was so good the excess resin had no choice but to make its way around the rails and onto the top of the board. So, when I unveiled it this morning, I had paper towel and rag laminated to the rails and here and there tacked to the outer edge of the board.

Had I not been using white pigment on the bottom it wouldn't have been any real issue. Just a bit of sanding back. However, the white pigment stuck out like dogs balls and so the amount of time needed to work it back to invisible grew exponentially. Foretunately the resin hadn't penetrated into the balsa on top so was relatively easy, though tedious, to peel back while the resin was still yet to completely harden.

It took about 2.5 hours to scrape off and sand back the overflow but in the end it came up ok with the exception being parts of the rails that look a bit scrappy.

Lessons learned:

i) Never place anything weak material directly on the surface of the board or directly in contact with the resin where it will be in the way for further work. Always use some type of release material and bleeder material to soak up the excess.
ia) Tape off the areas where you can't afford to have excess resin flow.
ii) Cover the board with bleeder material well beyond the edge of the board to soak up excess resin before it has the chance to flow onto the top.
iii) If you can't afford to have pigmented resin on the top surface of the board and you build the board up with layers of core material, it might be better to only prepare the lower part of the core, laminate that then put the top layer on the board once the bottom laminate it done. You could leave it on the rocker table (stuck down) and work on the core and then top laminate in situ.
iv) (After thought) If laminating top and bottom in separate runs, then leave the bottom laminate stuck to the table to that when you laminate the top no resin can flow under the board and mess the finish on the bottom.
v) Random though - I really struggled with getting the vac film off last time because the tacky tape was was damn sticky that it stuck fast to the film and so it stretched in every direction before it let go. This time I took it off early morning when things where cool and ripped it off in one might pull. It came of perfectly!

Tonight the top laminate goes on!!!!

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