Foam Molding Techniques
Johnson built three small F3Fs in total (above), each a little lighter and more detailed than the one before. His final version weighs 5 ounces when flying and spans 27
inches.These fuselage shells (at left) are for a future project, a Henschel 123. Making multiple pieces is easy once you have the molds.
Molding compound curves for fuselage sections More advanced technique is needed to mold compound curves, but don’t panic yet because it’s not really so bad. Choose a foam thickness to suit your needs. Single-faced foam has one side with a strong skinned surface and will con- form to the tight compound curves of a small fuse form. 1mm double-faced Depron foam will make compound curves, but will need some special handling to avoid major creases during clamp-up. This is suitable for larger models or models with a framework below the foam sur-
face. For small models you might try sanding one skin off the foam before molding it. Clamp your foam to one side of the fuselage mold first. Place the first clamp at the largest radius of the mold (usually the forward cen- ter of the fuse). Work out from there and space your clamps about 1⁄2 inch apart for thinner material.
When one side is clamped up, place the form on your table and begin to gently roll the foam around the form. Trim the foam to size and start clamping-up the other side placing your first clamp at the largest ra-
dius. Work your way outward from there and pull the foam down as close to the form as you can. Try to avoid making large creases— four small wrinkles are better than one large crease. The foam will shrink in the oven and the wrinkles will disappear, but the closer you can get the “cold” shape, the better. Adjust your clamps on both sides so the foam is drawn evenly to the form. Space your clamps side by side with smaller parts, or space them about every inch for larger parts or thicker foam.
Throw your part in the oven for about 5
Clip the foam to the center of the form (above left) then work toward the ends. Once the first side is started, move to the second side, continuing to adjust the clips to get the foam as smooth as possible. As you can see, there is no such thing as too many clips. Keep working the foam around the plug (above right) until you have it clipped as smoothy as possible. The bumps and wrinkles on the
example shown here did shrink and smooth out while in the oven. A typical mold for a complex shape such as a fuselage. Note the two flanges (below left) glued to the backside as anchors for the bulldog clips. Carefully trim the molded foam part (below right) while it is still on the form. A new blade will help minimize any tendency for the foam to tear.
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