On a 100" model, I will go through close to a half a box of each. Keep changing the blade. You can save them and use them for cutting balsa on other projects, but they seem to accumulate faster than you can use them up in building. Getting nice clean cuts is more important to me than saving a couple of bucks on the blades.

An alternative is to get a Whet Stone and sharpen the knife blades as they dull. It takes more time than it's worth, in my opinon, and disrupts the flow of covering.

I have half a dozen handles for the blades and change them all at once.

When I am making designs with film coverings, I cut on a sheet of glass. You peel the backing off first, then press the film down, rubbing out the bubbles. Use windex or soapy water if it won't stick. Don't press too hard with the blade, it cuts easily on the glass. If you are cutting circles, or arcs, a compass can be put in place without puncturing the film by using scotch or masking tape where the point of the compass goes.

Another cute trick is to use Scotch #811 low tack scotch tape. It holds, but comes off very easily. You can even do butt joints with it and iron it without problems, then remove it without residue. You can tape to the glass, or mat, or to the film itself. (They even make it double sided. Get your wife some for putting pics in a scrapbook and the pics can be removed later without damage)

JR