Aviater,

The reason for some of the deep "gouges" running the span of your core is due primarily to a non-uniform wire travel speed. To slow (or stopped momentarily) and it melts out a groove. When you try to control the speed of the cut at both ends by yourself, you will invariably get the result seen in your photo, especially when the wire is too hot. When the wire is at the correct temperature, there will be very fine whiskers attached to the core and the kerf width will be no wider than the wire. If the melted out area is any thicker than the wire, then it is too hot. It is nearly impossible of one person to properly control the speed of both ends at the same time. Best to get a helper. If you are in a model club, I bet there are several people who would be willing to assist and learn along side you.

Assuming that you will eventually cut symmetrical or semi-symmetrical wing cores, be sure to mark the ends of the foam block with a cord line reference line to align the templates. Be sure these lines have no relative "twist" between them or you will get a twisted core. When cutting the cores, always start at the front of the foam block on the cord line and cut back to the leading edge of the template. It is important to cut in slowly to the leading edge to give the wire time to "catch up" in the middle of the span. Otherwise, the leading edge will not be straight. Don't wait more than a second or two at the leading edge before starting cutting the upper surface so as to avoid melting a groove along the leading edge. Be sure the wire is stretched tight. It will get longer as it heats up and loosen some, so the cutting bow needs to have some form of spring tension on the wire to keep it taught as it heats and cools. If the wire starts to faintly glow at any time, then the temperature is dangerously too high... by about 500 degrees F or more. Be sure to do all cutting either outdoors or in a well ventilated and exhausted area, as the styrene fumes from the cutting process are very bad for you.