Moldmaking time on the Forward Fuselage! (FINALLY)
To prevent the 3D printed shell masters from possibly getting distorted when clay is pressed against them I laser cut an 'eggcrate' system of acrylic supports that were slotted together and then held in place by machine screws through the bottom of a mold base laser cut from 1/4" acrylic. The 1/4" base was cut to the desired overall size of the mold, about 3/4" larger than the part all the way around. The shell pattern fit snuggly onto the supports, a little water soluble white glue making sure it stayed put.
By not actually gluing the eggcrate supports together and by attaching them with screws through the bottom, I will be able to unscrew and remove the base and supports without the possibility of pulling the cured mold rubber away from the pattern, ensuring cleaner seam lines and minimum flash to clean up on the castings.
I built up clay around the shell patterns up to the desired parting line, carefully making the edges were as clean as possible, again to ensure a clean seam line. I used WED water based clay from Laguna Clay for this. Once the clay had hardened a little bit I cut half-dome keys into the clay with a ball end mill.
The mold box was made by gluing walls of styrene sheet to the edges of the 1/4" acrylic base.
After the silicone rubber was fully cured the styrene sides, mold bases and eggrate supports were carefully removed and the water clay removed. Careful cleaning of the surfaces with clean water and soft brushes eventually removed all the clay residue. That it the reason I prefer to use water clay over oil based clays, the residue is much easier to clean.
The next step will be to build a mold box around the first mold halves and pour the second halves. Being sure to use a little mold release to prevent the silicone from sticking to itself.
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