Weird tracksaw precision

[Holmes Anderson]

I don't think the Makita saw or track is the problem. That isn't a surprising amount of error for trying to square up a panel along that length of cut relying on a 12" combo square and pencil line. The problem is that even small deviations from 90 degrees create unacceptably large errors over a long span because the error increases in proportion to the length of cut. I think a deviation of only 0.1 of a degree will result in the error you describe. You might try squaring up the beam edge of the track against a big t-square like an accurate drywall t-square but for efficiently and accurately squaring up panels with a track saw I think you need something like an MFT (emphasis on efficiently and accurately). Better yet, get a sliding table for your table saw. If you have unlimited time and patience then I guess try a bigger t-square.