There are several bolts on the XYZ parts which are tough to snug (The outer most on the top and bottom). It looks like the design expects the plastic part to hold the hex in place while you tighten it but this proved no match for the nylock nut even if I broke it in first.
Yeah, the fit 4mm nuts well, 5/16" less so. That one feature on that one part was the basis of the entire burly mod. I fully understand to some it is a pain but it helps more than you know. For most breaking the nylock it makes it work just fine, sorry you had difficulties.
Honestly this machine is incredible and easily the most complicated 3d printed device I have ever built, so if getting creative on a couple of nuts is the extent of my problems, this is an amazing build. Was just trying to share some suggestions for easing the pain.
If it were something that frequently needed to be removed or adjusted, I’d agree with you. But since you basically never touch it again, sticking a small flat head screwdriver between the nut and the plastic is fine.
One place I would like to see a better captive nut is the DW660 clamps. Since that tool is (sometimes, by some people) periodically removed to swap out an extruder or pen mount or laser engraver, a captive nut glued into place on the back of those clamps would make that a lot easier.