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Build Log
Supra building: Mold making
In previous installments I have shown the plug for the pod with the pylon. I have done the mold now after many roundabouts. At first I made the plug with two halves thinking that it would be easier not to make a parting board. The result was two plug halves which were skew. I had to glue the two pieces together and do the finishing again (read lots of elbow grease). So now you know I am really not an expert and learn all the way. I made a parting board and the rest can be seen in the photos. I did not cut the board very accurate so I had to fill the cavities with clay between the plug and parting board. The complete setup took me less then an hour. What worked for me is to wax the plug and parting board and buff it by hand until it is shiny. I cover it with PVA mold release from Mica using a foam brush. When Dry I coat it with epoxy resin and fill the corners with a Carbosil mix. I found the carbosil mix should not be to thick as the bubbles do not escape then. I wait some time for the epoxy to get sticky and start with the layers of glass. I use a brush to tap it into all the corners and to make sure there is no bubbles trapped between work piece and glass.
After many thought I made a six piece mold for the fuz, nosecone and the servotray. This helps when you have to join the halves as you have access to epoxy the seam. The servotray was still a difficult shape and I made a joggle plate in order to create a offset for the one halve to fit inside the other. I fitted the plug in one half of the mold and cut a piece of 5mm hardboard to fit round the plug on top of the mold half. The gap is the sealed with body putty in order to get the shape of the plug. Once this is cured the joggle plate can be cut at the nose end in two. Position the two pieces over the mold half to create a overhang just enough for the thickness of the skin. The joggle plate worked fine but did not survive. The nose cone and fuz main part did not need this as I have lots of access space. I used the pretty Mantis fuz up to now with my Supra wing and have some experience with the pylon mounting. Due to the hard landings we experience at the local competitions the pylon is prone to damage when the wing twist on a hard landing. I saw in one of the RCgroup forums mention is made of solutions which includes a rubbery insert between wing and pylon base. This helps prevent the wing from twisting on its base. Meanwhile I found a rubber paint which is used for coating tool handles and applied this to the base of the wing. It helped so much that my wing broke next time, plastic bolt still in one piece. Additionally I fill the pylon with 12mm thick endgrain balsa (like the way the spar works) The grain runs 90 deg with the center line of the fuz, parallel with the wing and prevent any twisting which bursts the pylon open. I used to use acetone to clean the brush and tool, but normally the brush and acetone did not last long. I tested the Polycell brush cleaner and it works fantastic. afterwards you can clean the brush with water and it is soft again. The solvents available nowadays is brilliant! The Brush cleaner is expensive but overall I get far with it and use less brushes. Cheers Gert |
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Last edited by GNieuwoudt; Apr 22, 2007 at 08:13 AM.
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Lyk goed Gert! Wanneer begin jy komersieel vervaardig..... ;o) Ek kry so min tyd deesdae vir bou dat 'n RTF kit (yuck!!) al begin aantreklik lyk....
Waar was jy die paasnaweek, ons het 'n fantastiese naweek in Volksrus geniet. Drie dae uit die suide uit met 'n maksimum van 86km/h op Saterdag. Groete Izak |
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