So I am trying, in vain, to make some 45* miter cuts to have a (mostly) seamless box. Having the miter saw on a flat surface, I check the square of the blade to the fence, fence to the work surface, and work surface to the blade. Everything was aligned to be 90*. Although not purely scientific, I made a cut at )*, turned over the waste and checked for fit.
I then used a framing square to align the blade (made sure not to rub on a tooth of the blade) to the framing square. The blade was pointed to my left. I cut off the edge of my 1x6" to give me something to check with my square, appeared to be spot on. I then left the blade to the left, and cut each board. When I needed a reciprocal angle, I rotated the board, and left the blade pointing to the left. I should also mention I borrowed this guy from my dad, who has used for about 200 cuts total.
When I went to glue and screw everything together, my miter cuts were > 90*. My guess is around 100*, maybe 105*. Needless to say, this was a huge frustration. I also discovered that using 18ga nails into a scrap piece wont hold the joints for crap.
The most annoying part: The scrap piece seemed to fit/align perfectly.
Where am I going wrong with my calculations/methods of aligning the blade? How do you make sure you make perfect cuts on any saw, be it miter, chop, or otherwise?