Friday, June 24, 2011

Molded Beam - Fail

The first molded beam was a total failure.  The part turned out so, so, but I had to destroy the mold to get the part out.  All the waxing and mold release worked perfectly with the exception of an area on the top of the beam, about the middle for about 20 cm.  This area stuck so bad, the beam still has plywood bonded to it.  Needless to say, I was very disappointed.  However, I didn't get that discouraged to scrub the entire project.  I got out the plans and modeled the beam using a CAD tool and sent the model to a local composite prototype company that often does work for Mercury Marine.  They looked at the design and wanted to meet with me to discuss the project.

When I described all that I had done with my attempt they came up with two suggestions that would have probably gave me success.  First, the suggested that the mold should have been built so it would split or for a side to come off.  Once this suggestion was made, I saw how simple it would have been to make the mold split in half.  The other suggestion was to change the process of laying up the part.  In the instructions, Ray states that you apply a coat of resin to the mold and let it tack up.  Once it is tacked up, you start to apply the cloth as per the laminate schedule and you can not stop until you finish.  The composite company told me that when you lay up a laminate using this method, the part will shrink very tightly to the mold and if the mold is a light weight plywood mold like this mold, it often will suck the mold in when curing making it almost impossible to remove the part.  This is exactly what I experienced.  The composite company suggested that I should have let the first layer of the laminate (chop cloth) fully cure before adding the remaining layers.  This will greatly stiffen the mold and probably prevent the distortion of the plywood mold.

I then talked to them about what it would take to have them make the 4 parts for me.  I instructed them to give me a quote for 4 molded beams, untrimmed and unfinished.  When I got the quote for the mold and four parts, I told them to proceed with the build!  I figured the little extra money was worth knowing the beams will be built correctly and not fail.

Since the beams are under way, I will now focus on building the hull, floats, and finishing the centerboard.  The seven sheets of plywood on the workbench are for building the two strongbacks.

More to come....