MATERIAL SHEAR TIPS - OVERVIEW
1) Do not trust the ruler.
2) Do not trust it to be square.
3) There is a major difference between a metal shear and a flex shear.
4) Unisub FR may be shear cut under certain conditions.
1) Unless the ruler is engraved it is made of a plastic material pressed onto metal. It streaches when pressed. I have 2 trimmers and both rulers are off in different places. It may be perfect at 2" and 8" but can be 1/16" off at 6". Cut flex strips about 1" to 2" wide of precise lengths that you use by setting the stop with a metal ruler and then verifing the length. This will be the lengths that you will cut in the future so be precise (or the faintest bit under to guarantee not being 1/32" short in the last cut of a section of a sheet). Carefully bond them together (using Res-N-Bond or equivalent) going from the longest to the shortest to make a pile. Be sure that the common edge is even. This block can be placed easily against the blad at the length that you want while you set the stop. Due to there being a longer strip on top of the length that you want it is easy to hold in place. I Score lines on the surface to show exactly there the under strips are and mark them to make it super to place in the proper place. If you use many lengths better to make a few blocks than to go over 1/4" total thickness. I have one for 1/4 & 3/4 markings and another for 1/2 and even inch markings, plus some for oddball lengths that I commonly use.
2) Invest a very small amount in a machinists square. It is an L shaped picec of steel one foot by eight inches. It is thick enough to remain square. Align your ruler/guide with this. After aligning you can test by cutting a 6 x 6 piece of material by shearing each side in a clockwise progression. You will never get it perfectly square but you can see how far off it can become, shoot for very little. Cut a piece of scrap about 9 x 9 (hopefully you do not have many of this size scrap) mark the corner of the last cut and side that was against the guide. This makes an excellant push/align guide for last pieces of a set of cuts. When you buy flex have it split lengthwise unless you have a 48" shear or need things bigger than 12" in both directions, which needs hand cutting.
3) The shape of the blade is critical for the material being cut. Plastic ain't metal. A plastic blade is very sharp so as to cut into the plastic as it shears. A metal blade is much blunter to tear the metal apart at the cut. Metal will easily chip a hardened plastic cutting blade. (I believe that the bottom blade is the same.)
4) Yes Unisub FR can be shear cut somewhat. You must use a metal shear, the fiberglass reinforcement may microchip the plastic blade. The trick is to have the material at 80 to 90 degrees Farenheit. Too cold and you get bad chipping and a very rough edge. Too warm and you may put a crack at the edge of the surface at the cut. Too hot and the plastic will powder at the edge from being torn by the fiberglass as it is being sheared. If you need a perfect edge for a badge you will have to quick sand the edge.