It may be that the slots are not in line with each other. If they make a V
to the inside or the outside of the mitre the joint will align with the slot
and not the mitred edge. This would give you a gap at the inside or the
outside of the joint.
Let the rest of us know what the solution was when you find it as it may be
of some help to others.
Jim
"Toller" wrote in message
...
I made my first biscuited miter joint last week; with two 15" wide panels
and three biscuits.
It did not come out well; no matter how much I fussed with it I couldn't
eliminate the gap. Possibly no one would have noticed it, but I sure
didn't like it. (it couldn't have been too bad, as it held my full weight
jumping on it...)
So, I am redoing it, being more careful that my cuts are perfect, and only
using two biscuits.

Well, when I dry-fit it, there still a gap I can't get rid of; the gap is
uniform all across, so my cuts are good. I marked up a biscuit with a
central line, and the central line falls exactly on the edge of the slot.
I have thinking that maybe the clamping on 90degree joints is adequate to
make it work, but the clamping on 45degree joints won't push them
together, and I have to make my slots a hair deeper.

Does this make any sense, or is my problem likely to be elsewhere?

I am not thrilled about the recutting my slots, as they are likely to end
up a bit wider than I would like; maybe I can get away with just deepening
one side?