Foamcore



Foamcore is a material made up of foam sandwiched between 2 pieces of paper. It is great for many things, large models being one of them.

This article is intended to help with the construction of quality crafted foamcore structures. It is most likely too time consuming for quick and dirty things. If you just need some foamcore stuck together and do not care about its appearance, just hot glue it. The joints are just for presentation purposes only, and are non structural.

Working with foamcore
'''White foamcore gets dirty really easily, so unless you must use white, or you do not care about it getting dirty, use the black stuff. It looks cooler to boot. But do not use black for a model that represents a white structure.

While x-acto blades are popular to use, a good sharp Olfa blade will cut through the fomecore with half the effort and give you a nice clean edge on the foam. The back of an olfa blade also works well to scrape foam off of the paper when making a rabbet joint.

Joints


A rabbet joint achieved by removing one of the layers of paper and the foam just enough to set an other piece in the removed area. This makes it so the remaining layer of paper covers the end on the other piece leaving you with a nice neat barely visible seam.
 * Rabbet Joint (see image)

First, mark the area to cut away. This should be the exact depth of piece to lap over. Using an exacto knife, make several passes to cut through one layer of paper, and the foam, but not the 2nd layer of paper. Then use the knife to separate the foam and cut paper layer from the intact paper layer. If you are using 1/4in foamcore, you should then be left with a 1/4in strip of paper layer that is sticking out.


 * Miter Joint (See Image)
 * A miter joint is achieved by cutting two pieces of the foam core at a 45deg bias. When brought together, the two pieces meet at 90deg, and have a very small seam at the corner. The miter is nice because it can efectively be used to creat a joint at any angle. If you need the pieces to meet at 60deg, you just cut each piece at 30deg. 120deg, each piece at 60, and so on.

Make sure your blades to cut the foam core are really really sharp. If you can use a new blade. A dull blade will leave tattered paper on the edges. An exacto-knife is recommended for working with foamcore.


 * Seamless Miter Joint (See Image)
 * A truely seamless miter can be achieved. For this example say you have a piece that is 10 in wide and you want to make a piece that has 5 in pieces at a right angle. Instead of cutting the piece into two 5 in pieces, you could fold the two 45deg cuts so that they meet at the 5in mark. The trick is that you do no cut through the 2nd layer of paper, so you have a 90 deg angle taken out of the foam, but the board is still intact. Then just fold the board so that the gap comes together, and glue. You have a miter just like you do above, but there is no break in the paper. Obviously this is harder to do though.


 * Seamless inside joint (See image)
 * A really simple seamless joint can be made for inside joints. Just cut straight down through the first layer of paper and all of the foam, and fold. Then use low temp hot glue to hold it. High temp may melt the exposed foam.

Glue
The best and most often the strongest glue for foamcore is hot glue. Hot Glue works perfectly on foam core, as long as it is paper to paper. The hot glue can melt the foam, so if you have exposed foam, it may not be the best. But hotglue is the quickest, strongest glue you can use with foamcore. Low temperature hot glue may work without melting the foam, but test it before applying to your final piece.

Tacky Glue and Sobo are also very good adhesives for foamcore. They dry clear and flexible and do not leave those grody hot glue strings. They also won't melt the foam. Though Sobo and Elmers are both PVA glues, Sobo dries flexible While Elmer's does not, so make sure you are using the adhesive that you want.