How to Create a Foam Prop Project

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When you think “Foam” think of “Props” – Foam can be used to create any size and shape of props, from as small as a grain to as big as a life size airplane, boat, tank, sky scraper and more.

Props are used by endless number of industries for endless number of uses, including films and movie sets, theaters, monuments, signs, architecture, art, museums, trade shows, displays, booths, amusement parks, decorations and events, aerospace, aeronautics and many more.

But how exactly are these props made, and can you make them yourself using simple hardware store tools at home?

Smaller props that do not require detailing can definitely be created with hand tools by using carving and sculpting tools and hand-held cutters. The props can then be brushed with any type of coating and then painted. However, larger and more complex props require the use of a CNC hot wire foam cutter, a CNC router, or a combination of both.

First, a CAD file (drawing file) need to be created, so that the foam cutter will be synchronized with the computer to produce the desired cut. If the prop is a two dimensional one, a PDF or DXF file is mostly sufficient. For a three dimensional prop an STL file is probably the best choice, although other software such as Solidworks and Vectorworks will work as well.

If a CAD file is not supplied to the foam cutting services company, it can be achieved by scanning the item, using a 3D laser scanner. The scanner can increase the size of the item up to x20 times larger than the original.

The CAD file created is placed in the computer that is connected to the hot wire cutter or the router will create the coordinates for the cuts. The CNC hot wire foam cutter will then cut the 2D shape using X, Y and Z motions (horizontally, vertically, up-and-down) by melting the foam. The CNC router will machine the foam in drilling-like motions to create the 3D foam prop. Any 3, 4 or even 5 axis machine is suitable.

After the prop is cut, sanding it is usually required to give it a smooth surface look. If the prop required is a large scale one, it can be cut in sections, then glued together and sanded to erase any lines created by the gluing. If you need to give it a more natural look you can then use a hand chisel or a knife. For example, you can carve bricks into a foam wall, carve letters into a tombstone. There are cases where the 3D model to be designed is either too large or too thick to be machined due to height or cutter length restrictions or the foam material not being thick enough. If that is the case, the shape can be sliced into sections. Each slice will be machined separately using the router and then the pieces can be glued together. The machined parts can then be sanded and coated with protective hard shell and painted, which will also take care of eliminating any visible grooves due to the gluing. Routers can also be used to create molds that can later be poured with concrete or polyurethane and other casting materials.

The next stage would be the coating. To make the prop stronger and durable you need to coat it. If you need a hard shell coating you can use polyurea. This type of coating combines high flexibility and durability with high hardness and is fast drying. It can be sanded to a smooth finish and can then be painted with any type of paint – water-base paint, including latex or any oil-based paint, as well as automotive paint. It dries in minutes, providing a tough chemical and abrasion resistant coating. Polyurea will not provoke blistering and blistering will not occur even at extreme temperatures or in humid environment. It will also resist yellowing from ultra violet light exposure. Since the polyurea dries very fast, it requires fast and efficient mixing and spraying techniques, thus, spraying a large foam piece with a spray gun is the smartest application method.

Coating can also be made using polyurethane or epoxy, but it will not be as strong as the polyurea hard shell. The last stage is the painting and at this stage, the artistic abilities are often required. Painting might require detailing to resemble the original picture or project, mixture of different colors to create special look, for example a rusty-look, antique-look and more. 

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