canadafins
Hello, this is off of the boating theme a bit but the general principals still apply. I love vintage boats but I am also into building and flying large scale RC aircraft, specializing in WW2 fighters. I have made a number of molds over the years for various large scale airplanes so I thought I could show how it is done. First one must build the plug for the mold, this can be scratch built or working off an existing piece. The subject I am making a mold of is a 110"wing span Corsair. It is important to close all openings and add all details such as panel lines before starting the molding process.. Brad Lake (Canadafins)f13.JPG
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canadafins
Next the final plug must be finished with a surface that is impervious to resin such as epoxy paint. f1.JPG 
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canadafins
For reasonable size molds such as this I typically cut the shape of the object out in a 5/8" thick melamine board by carefully tracing it with an extended pencil then cutting with a jig saw. The remains of the melamine board was used to make the box to raise the mountaing board.f2.JPG
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canadafins
Once you fit the board to the plug the plug can then be temporary hot glued in from the back side. I typically put  small amounts of masking tape on the the plug then glue to the masking tape so as not to damage the plug later when releasing it from the board. We will be laying up half the mold using the melamine board to form the flange for the first half of the mold. Once the first half is made the plug will be removed from the melamine board  with the plug still in it and the second half of the mold laid up on to the now existing flange and other half of the plug. f5.JPG
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canadafins
Next the gap area between the plug and the melamine board must be filled with modeling clay (the type the is always some what soft and flexible) so there is a nice sharp  transition from the plug to the melamine . The modeling clay can be warmed up in a microwave if it is too stiff to easily use. It is important to force the modeling clay down into the crack so when you trim it off flush it will stay properly. You can see how the clay fills everything including the chips in the melamine from cutting with the jig saw.f8.JPG
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canadafins
Trimming the modeling clay flush using a old gift card. Gift cards can be had by the hand full at Walmart if you ask and work great for this type of thing or spreading bondo or finishing fillers. f9.JPG
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canadafins
The plug is now attached so 1/2 of it is showing and any gap  filled including the  chips in the melamine caused by the jig saw.f11.JPG
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canadafins
Now that the plug is nicely sealed to the melamine board the next step is to wax the plug and about 3" of the board around the plug about 8 times with mold release wax.The next step will be to spray the plug and melamine with a product called PVA that is intended to help release the plug from the mold when finished. If you thin the PVA with alcohol instead of water it sprays on smoother with less orange peal that would then transfer to your mold.f10.JPG Brad Lake     ( Canadafins)
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KevFin
Excellent and informative posting Brad.  Thank you!

-KevFin
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canadafins
Here is the next step in the molding process, the fuselage was first sprayed with a few thin coats of PVA mold release than a generous coat of gel coat was sprayed on. The first layer of mat fiberglass will be applied after the gel coat dries for about 3 hours and before 24hours...Brad LakeIMG_1628.jpg
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canadafins
Fiberglass mat is then cut to the size of the Fuselage and enough extra to form the 2" flange that will be around the outside of the moldd1.JPG 
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canadafins
Having the proper tools is important, for this mold I am using 2" disposable brushes and small diameter rollers to get out the bubbles that will form between the mat and the plug.These rollers are available at body shop supply places that sell resin and gel coat. They must be dissembled and cleaned in acetone after each use.
I also ran a fillet of bondo around the entire perimeter of the mold with my finger to eliminate the sharp 90 degree bend the mat would have to try and make.  Mat will easily follow a fillet but 90 degree corners are trouble and often the mat will pull away. Best to avoid sharp angles  by simply putting in a fillet of bondo or resin thickened with micro balloons.d2.JPG
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canadafins
Next a quart of resin was mixed up with 2% hardener added, resin was then quickly brushed on to the mat and allowed to soak in for a few minutes. Here is shown brushing resin on to the fuselage plug before laying down the mat. You can see the bondo fillet around the perimeter of the mold. Two of us worked quickly at brushing and rolling to ensure getting finished before the resin kicked.d3.JPG
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canadafins
The mat was quickly covered with resin not spending any time trying to work it in, new resin will soak in much faster than old thicker resin making the job easier. If your resin is too thick it can be thinned with acetone, thick resin is hard to use as it doesn't penetrate the mat very quickly.  d4.JPG
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canadafins
Once the mat is all saturated with resin the rolling process can start. The first layer of mat is the most important and must have all the trapped air rolled out.d5.JPG 
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