Oh and mark where you want to cut with a perminent marker first!

Also don’t worry if its a bit uneven as what ever covering you have over it will disguise it.
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Many, many years of sewing and costuming.

This multi-speed, hand held tool can take a wide range of bits, and works fast. You have to wear safety glasses though, so bits of plastic don’t shoot into your eyeballs. Most Hardware/DIY shops, and some craft / hobby shops will carry some form of Moto Tool. (Dremel is my current brand, but Black and Decker makes one that has more torque and better speed control). My 3 favorite bits are:

Metal Grinder bit (in the tool above)– good for cutting out "keyholes"- turns your moto tool into a drill saw! Hold at a slight angle to cut into plastic without having to cut from an edge. Great for making doorways, window holes, etc. Also good for making small, half round notches in things like Eldar terrain or for pipeline guides.
Fiberglass reinforced Cutoff wheel (left)– Cuts through plastic and wood quickly! You can use these to make doorways too- they give you a straighter line, but you’ll have some trouble cutting the corners all the way through without overcutting (cut from the inside if you can, to hide overcuts). The fiberglass wheels last MUCH longer than the stone ones, but cost more. If you need to cut metal, use the stone wheels- they won’t last any longer, but are much cheaper. (Or consider using a hacksaw instead).
Drum Sander (right)– If you need to remove material quickly, or sand a curved shape into something, this is a great tool. Use the rough sandpaper drums- the fine ones tend to clog too quickly. Like the metal grinder, it can also be used to cut half round notches into edges.
One last note- a Moto tool is very useful for adding "weathering" to your terrain, particularly the kind of nicks, scrapes and cuts you would see on stone, wood, or beaten metal. The Cutoff Wheel is the best choice for generating these effects, though the other two bits can also yield good effects. I use two techniques- Tapping (repeatedly dropping or pressing into the terrain, to form nicks, chips and dents), and Dragging (lightly drawing the tool along sharp edges and corners to round them off). Example applications include:
Adding score or seperation lines to represent Stone work (best seen in the Aqueduct and River pieces)
Adding nicks, chips and cracks to make more convincing Stone work (again best seen in the Aqueduct and River pieces)
Adding dents, chips, and other weathering to Metal work (best seen in one of the Space Hulk pieces and most of the Ork terrain).

RAZOR SAW

Aside from it’s uses as a terrain tool, this fine-toothed, thin bladed saw is the ultimate tool for conversion work. Use it wherever you want to preserve both sides of a cut, or wherever you need a neat, clean line. If you want to save money, just buy the "blades" and don’t bother with a handle (I find I get more control by gripping the blade directly anyway). Razor Saw (blades) are available in most hobby stores. TIP: When cutting through pewter, resin, or hard rubber, the blade tends to "bind", making cutting a slow, laborious process. Speed things up by rubbing some lip balm (I use Chapstick) directly onto both sides of the blade. This acts as a lubricant that helps the saw fly right through for a faster cut!

Easy to Form. Unlike styrofoam, foam rubber is easy to shape and to add texture- cut it with a serrated knife, or just tear it apart with your bare hands! No more hot wire cutter incidents… Once you have a general shape you like, you can add more detail just by "pinching" and tearing away small bits of it. This is a great way to make rocky crags, especially if you rip out vertical strips, forming "gullies". Note that you can buy it in any thickness, and because it starts out flat on both sides, you’re guaranteed to have a nice, stable surface on top to put miniatures on, plus you can stack them to make taller formations if you wish.
Easy to Paint. Unlike styrofoam, foam rubber will not "melt" away when you spray paint it. It even comes in a variety of colors, though you can spray it to be any color you like if you’re persistant. Build up your colors in layers- for example, for crags I usually start with flat black, then add grey and brown highlights. When spraying the highlights, come at it from the sides, so only the edges that stick out the farthest catch the paint. This emphasizes any shapes you ripped into it during the forming stage. You can also "dust" it from above to highlight the top edges- this can be very effective, and very quick too! The tiny pores in the foam catch spray paint well, so you won’t need to do any hand painting or drybrushing.
You can paint with it too! You can use foam rubber to paint large areas quickly. Just dab the foam into your paint, and dab the foam over the area to be painted. You’ll get a nice, even, grainy texture that can be put on heavy or light for different shading effects. This is much like drybrushing, but faster and easier (though not very precise).
Also a good tool! When cutting sharp, pokey miniatures with a razor saw, it is often hard to hold onto the model. Try wrapping it in a piece of foam for a soft but sure grip (blister pack foam squares are great for this). Also, when bending metal parts, you can reduce "tool marks" caused by sharp plier edges by wrapping the piece in foam first.
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