Not a three way miter, but an alternative. More fragile. Pictured is a display stand post. It is 1" square cherry with a 1/8" kerf for the glass. The miter on the inside is 45 degrees to increase the sight lines. The post is just that and is anchored through a base by a smallish #4 long screw centered through the large area at the point and through the base. Sort of like a tent pole. It is a butt joint aligning the posts glass kerfs with other kerfs in the base and glass kerfs in the mitered wood top that also has a dado holding 1/8" glass set in as the top. The whole is carried/handled by the base and accessed by the recessed glass at the top. Sorry for the old pictures. There is no pressure on the post that a screw holding the post cannot handle given the glass kerfs in the base and top, but it is only for static display. With all of the components in place it has lasted twenty years. An identical post set up has worked in a tall mast pond yacht display case,(26l x 9w x 38h) but plexiglass was used there as tempered glass was too heavy.