I know that joints should always be tight, but I suspect my dadoes are too tight.
I have done a couple of projects using dado joints. I cut using a router, either using a 3/4 inch bit, or using "undersized" bits for plywood. (I've either used an edge guide or clamped a board as a straight-edge, and this has generally worked quite well.)
When dry-assembling the joints, I usually need to use a lot of force by hand or a mallet to seat the parts and to take them apart. Sometimes I need to lightly sand the joining board thinner in order to fit. So I would say these have been very tight.
When I glue the joints, I am not always able to get the parts to fully seat in place - even using a mallet and clamps as tight as I can make them. I apply glue (Titebond III) to all contacting faces first. It feels like the glue quickly sets and I can't move the parts fully into place, but I suspect the grain is swelling so it doesn't actually fit anymore. Without being fully seated, the glue is only bonding at the edges of the joint, and I suspect it isn't very strong.
For past projects this has been "good enough" if not fully satisfying, but for an upcoming project I will need the precise fit and full strength of the joints.
I can't really adjust the width of the dado finely, but I could sand the joining boards more to achieve a looser fit.
Is there a good way to know if a dado joint is loose enough to glue properly, but not so loose as to compromise the strength?