"Edwin Pawlowski" wrote in message . com...
"Curmudgeon" wrote in message
. ..
Your mitre saw ain't "true"...either the grooves in the mitre box are worn
too large, or the blade angle on your power mitre saw is out of line.
1. Buy a new, good quality mitre box( and back saw)
2. Do an alignment on your blade (read the owners manual)

What if the tools are true but the walls are not? That is very common.
Ed

I would guess that in at least 95% of the cases it is the corner that
is not square, not the tool. Of course aligning the tool is always a
good idea.

Harry K