Tom, make sure you are turning it the proper way. All saw blades,
no matter what piece of equipment, need to have the nut the same
direction as the saw blade turns to remove. I assume your motor
is on the right, blade on the left and that it turns clockwise
when running. Turn the nut clockwise to remove.

As others have said, I'm fairly sure the saw has an armature lock
(the one that shows up on Amazon does). If you can't find one,
use a scrap piece of wood set just like you planned to cut it.
Cram the blade into the board. Turn the nut clockwise. If the
armature turns and the blade does not, there is a different
problem - the threads are hurt or the nut is rusted on.

--
______________________________
Keep the whole world singing . . . .
DanG (remove the sevens)




"Tom" wrote in message
...
Black & Decker miter sale model 7715 type 3.

I bought this saw at a garage sale. the seller cut a board, said
it
needs a blade. But, I can't remove the old blade. The armature
of the
motor turns when I try to turn the blade nut. If I "jam" the
blade so
it can't turn, the armature still turns. How do I lock the motor
to
remove the blade?