This guide outlines how to cut pieces of foam into airfoils with the handheld hot wire cutter.

Setup

Cut out block big enough to fit airfoil in. Leave extra space on top and bottom. If there is not extra space on the bottom the cutter handle might hit the table and be unable to cut low enough.
Measure out from the edges of the block, mark with a marker, and screw the 3D printed guides into place. Measuring out the hole locations ensures they are aligned with each other (assuming your block was straight to begin with).
Ensure that the nichrome wire does not have any defects, like ridges or excess hardened foam on it. This will result in a poor cut.
Ensure the nichrome wire is tensioned properly. If it is not tight enough bowing will occur during the cut. This will cause warped airfoils, and will cause especially poor spar hole cuts.
Draw a line with a marker roughly corresponding to the cut. Do not cut the whole airfoil with one cut. The wire should enter the foam and make contact with the 3D printed guide tangent to the curve. If you go straight down and then 90 deg to the side it will cause an unwanted indentation in the foam. Ideally, do one cut going mostly horizontally along the top, same along the bottom. The leading edge should not be cut directly with the hotwire cutter. The rapid change in direction will likely cause an uneven cut. It can be cut off with an exacto knife and sanded down.

Cutting technique

Cuts should be done by two people. One on each side. Write numbers with a marker on the foam along the direction of each cut. Then each person can call out the numbers as they cut. Both people need to listen to each other and stay aligned (don’t want one person speeding ahead or lagging behind).
No not push toward each other even slightly while cutting. This easily makes the wire lose tension and will result in bowing. If each person pulls with a very small amount of force while cutting that would be ideal.

Clean the wire aggresively with paper towl within 10 seconds of cutting power after each cut. The foam residue cools very fast and will become difficult to get off quickly. If too much foam residue is left on the wire it will not cut as well, and will cause small divits in the cut where droplets form.
Replace the nichrome wire if it is not tight enough and cannot be tightened. It will likely have to be replaced every 10-20 cuts or so. The wire can be replaced by cutting it carefully, and then feeding in a new wire and using the copper crimps that we have in the bay to secure it.
Unscrew the nuts on the hot wire cutter to reduce tension before storing the hotwire cutter away.

Nichrome wire gets hot and it is easy to burn yourself. Keep in mind not to touch the wire while it is on or immediately after turning it off.
The wire is sharp on the ends, so be careful when replacing it.