CJ in MPLS
Woodworking magazines tend to be rather cyclical in their subject matter. One of the topics that comes up periodically, as well it should, is the order of operations for fitting doors and/or drawer fronts into an opening. However I do not ever recall seeing the same type of article on the trimming of tenons or mortises to ensure a good fit. This topic is generally handled as an aside, i.e. 'take a whisper off of the tenon to achieve a good fit."

I have seen an article on undercutting the bearing surfaces of joints to ensure that the mating pieces pull up tight and I have seen the tip on spotting a joint (usually dovetails) with pencil lead to find high spots. However neither of these appear well aligned with fitting a tenon to a mortise as there are a few problems, the main one being that the surfaces being fit are not easily viewable. I can tell that the tenon does not fit, but I cannot easily discern which surface needs to be trimmed to free it up.

It is a given that a good practice is to first ensure that the joint has been properly marked, mortised, and sawn. In one sense, doing this properly may avoid the problem entirely. In another, it limits the nature of the problem to ones that are addressable in an organized fashion. If one is haphazard in layout or execution, the problems are likely to be much more complex. So to set the stage, I am really only talking about an organized approach to tweaking the joint and not a treatise on fixing the kind of cock up where the mortise is 1/8" too large or the tenon has an unintentional 5 degree complex angle to it.

I presume that one would start as one usually does in that reference surfaces are designated (male and female portions of the joint) and then inspected for any obvious defects. But from there I'm starting to rely on pecking away at the parts until something works, which in the end often results in a sloppier fit than I'm happy with.

To complicate matters, if one is dealing with through tenon (which is why I'm thinking of this), the distal end of the tenon cannot be willy-nilly trimmed until it fits as the distal end may well then be made smaller than the exit opening of the mortise. In this instance, my inclination would be to verify that the tenon tip and the exit of the mortise are indeed the correct dimensions, whereafter i would start to enlarge the mortise from its opening side. Throughout all of this I take long moments to breathe deeply and to banish from my mind the idea of swinging a mallet a bit harder to see if that works.

CJ