I sanded out the spar cap troughs using a piece of aluminium square tubing with sand paper glued to one side. It is perfectly straight and cuts evenly from one measurement station to another. The one challenge was that the M drawing templates didn't match up well with the actual dimensions listing in the actual plans. I measured it out about 10 times and my spar is perfectly correct, but the templates are too short to fit around the spar. I spoke to builder support and they said that the paper templates may shrink with temp and humidity and that is was acceptable to cut off the front tab. The templates were not particularly necessary with my router method of cutting the spar cap troughs.