I tend to cut mortise/tenon joints on the tight side and use the clamps to force the parts together.
These shelves I made when setting up my gallery booth with the 40 through tenons were a killer.
Add on to that that the original Bessys handles are slick as snot on a door knob, I used some channel locks to get a better grip. The softer metal where the clamp screw threads into was not to happy about that.
