This was originally posted at the TerraGenesis Forum and I figured I'ld share it with you guys.

Sputnik on cutting foamcore:

This was one of my first obstacles when making terrain. When I started playing 40K I went out and got foam core and an exacto knife and started cutting out and making what I had originally planned to be a bunch of imperial structures... well, they turned out to be orky... There's nothing wrong with orks, but it's not the effect I was going for. I have a couple of professional artists as friends, one of which went to Cal Poly San Louis Obispo as an Architect major. (all their projects have to be made out of foamcore) So I went out and asked them how to do it. I actually found a special foam core cutter made by Exacto. It's a small gray piece of plastic in a semi-circle with a black rubber handle. It has a special blade that's double edged, so you can turn it over and reuse it when it gets dull, which is unfortunately very quickly.

The number one most important thing is to make sure your cutting tool is sharp as can be. It will dull very qickly as I said, so I don't recommend using a utility knife unless it's brand new, but even then it will dull and you'll need a new blade. I recommend an exacto knife if you can't find the special tool. The blades are fairly inexpensive, and it can be used for small detail.

The number 2 thing that I found was that you MUST CUT SLOWLY!!! I can't emphasize that enough. If you cut too fast the foam core will bunch and rip, not to mention you could lose control and the line could become wavy. Also, I'm sure you do, but just in case, draw the lines you want to cut with a ruler, then use a ruler as a guide when you cut. I recommend using a metal ruler with a cork or rubber backing. This keeps it in place without damaging the foam core, and you can't cut into the ruler like you can with a wooden one.

Also, one thing often overlooked is your cutting surface... Do not cut on wood, it will ruin the tip of your blade. I usually cut on a short stack of newspapers or some cardboard...

Caitlin:

In my opinion, the most important thing is that the cardboard is cut neatly. Cutting through foamcore requires cutting more than once. I find that I cut 3-4 times on average to get through a 0,5 cm foamcore. The first cut will cut the first layer of cardboard and the initial layer of foam. Then the next cut will cut most of the foam and the last cut will take the last foam and the next layer of cardboard. If I am not all the way through by now, then the line I am cutting from will by now be showing on the other side and I will follow it from that side instead - that prevents some of the "orky" look. Taking the time is the only way I know to make anything look really good. And then - I trim my foam afterwards with scissors if it does not look alright.

Finally, I can really recommend covering the exposed foam with a slice of cardboard (on the finished piece). Whatever you do, the foam will not be perfect and it does not like spraypaint. To make the cardboard stick to the foam, I use white/Elmers/PVA glue and then I press dressmakers pins through the cardboard into the foamcore to hold it together. Either I place the dressmakers pins as rivets or I use the ones with the large heads and remove them afterwards. Sometimes pliers are necessary. If you don't like the fact that there are small holes in the cardboard afterwards, then I can recommend using the plain dressmakers pins and placing them as rivets. They are relatively inexpensive and look great.

If you are making a building using the standard foamcore techniques as described by Gary James, TerraGenesis, on his foamcore page, then I recommend making one cardboard strip of 1,2 cm wide and as long as your building is tall for each corner. Score the strip in the absolute middle with your knife. Now bend it at an angle and glue it onto the corner as protection for the exposed foamcore. I know that only one side shows foam, but making it an angle will give you an added feature to your building. Many buildings have cornerstones or cornerbeams of a different color or type than the rest of the building. With the plain dressmaker pins placed like rivets, you get instant detail and greater strength at the same time.