Ideally you should be able to stack one board on the other and see no light.
I usually shoot for the ideal since it means less stress in the joint.
I suppose a little light might be ok but certainly not 1/16 of an inch. In
relative terms I wouldn't consider that a little gap, I'd consider it a
As for gap filling abilities. Most common glues don't have any and what they
do have provides no structural strength. Epoxy or the like may do the job
but they won't take stain and, in a gap like that, will look like hell.
I'm not familiar with a busy bee but if it is a jointer and you can't get
the joint so you can't see light either there is something wrong with the
jointer set up, your procedure, or both. A properly jointed board has a flat
face. Not partly flat, not almost flat, just plain flat. When you put two
flat faces together there will be no light.
Accuracy in any joint tolerances can be summed up easily. The closer you
get to perfect the easier the project will go together and the better it
will look. The further off from true the joints are the harder it will be to
stick things together and the sloppier it will look. After that it is up
to what the individual woodworker's threshold for a good looking project is.
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