Parametric Counterbore Drill Guide

thingiverse

I put in a new floor. Now the bi-fold closet doors needed to be trimmed 1/2" because the door hardware was now not able to fit into the reduced vertical space. But I thought of a better way than shortening the doors. I could counterbore holes and inset the (one) bottom pivot and the (two) top spring-loaded pins. So I designed and printed a sacrifical centering jig which attaches to a 3/4" spade bit and allows one to cut a perfectly concentric counterbore despite there being a 1/2" hole already drilled. I also turned down just a touch the 3/4" hinge pin flanges so the fit would not be so tight into the counterbore. This worked perfectly. The 3D printed bits ended up inside the the door but they started the counterbore holes perfectly.