Squareness comparator I finished building today. I was planning to use ½" steel ball bearings for the feet and face but didn’t I didn’t have any in stock. Impatience caused me to improvise! I put a slight radius on some steel rod with my radius turning tool and sanded with progressively finer grit until I got the finish I wanted, then parted off at ½". Reamed holes at .499" then discovered the stock I used is slightly undersized anyways, so had to cement the feet in place with red loctite. The face is made from 5/8" material so rather than drill and bore a hole for it in the base, it’s just held on with a grub screw. This will allow me to make fine adjustments in the future if I need to, as well as replace the face entirely should the steel get damaged or worn with use.

Now all I need is a cylindrical square or a granite square/angle plate as a master. Unfortunately, I can’t make one of those. :[