To echo previous replies -
With a Morso the most common cause of gapping is dull blades. Once the pristine edge has gone
the blades will tend to cut slightly 'off-track'. Particularly if you have been cutting hard wood or
very thick synthetic gesso. The solution is the 'left-fence tweak' which I have explained to people
xxxxty times. Amazing how many framers don't know about it. Forget setting the blades to an angle
gauge. You can do this until the cows come home but the fact is the angles are so fine that you will
never get the blades set right this way. Except by dumb luck.
If the cut face is a fraction of a degree adrift then the error will cumulate over 8 faces. People get
baffled as to why the gap (typically on the inside) only occurs on the last join. If you think about it,
the first three joins will always be tight even if the angles are off. That's because the ends are free.
you simply can not tell that the corner is 89.99º. But when it comes to the last corner the faces will not
be parallel. Hence the gap.
You cannot correct the angle on the right hand blade. That is set in stone (or metal). One way is to lay a
stick in the cutting position
tight against the left fence. Then slacken the bolt and deflect the
far end of the
stick about 3" toward you. That will likely cure the prob. It will compensate for any angle deviation on
both blades.
Theoretically, this action will produce a different length on the right/left lateral miter faces, but in practice this
anomaly is sooooo small that you will never notice it.
The principle is the same on saws. I have two chop saws set inline. One does the left end and the other the right.
I slide the stick though and cut the right end. Then slide it further up to a stop and cut the other end on the other saw.
This not only saves swinging the head (which is likely to disturb the angle setting) but allows very fine calibration.
Saws of this kind that have a fine tuning adjustment on the set indents are few, if any. With my setup there is enough
play in the holes where they are fixed to the bench to skew the left hand saw a tad until it cuts true. It's worth taking
time to calibrate equipment.
My ideal situation is to end up with the two final faces
ever-so-slightly apart. The natural springyness of the v-nails
will make other corners flare out slightly. Pulling the last two faces together neatly cinches up all the corners all the
better for the glue bond.
** If you try this tweak and subsequently get gaps on the outside, you have tweaked too far.