The gray triangular structure sitting on the table is the jig that was used when machining the sector bearings. By re-fitting the original mounting screws and then cutting off their heads, it is precisely set in its original position and then readily serves as a polar alignment fixture.
My Platform
Top Board
The top board is just that platform which rotates as though it was mounted on an axle parallel to the Earth's axis. Of course, if it were, then there would be interference issues with any telescope, but by placing the bearings UNDER the Top Board, those are relieved.
What is left is the problem of building bearings which can constrain the rotation of the Top Board as needed. Chuck Shaw developed the idea of two cylindrical bearings which represent right sections of the cone of revolution. This simply leaves the problem of shaping these cylindrical sections, and Shaw and others came up with the simple idea of mounting the sections, roughly cut slightly oversize, on the platform's Top Board with a temporary mounting fixture that permits rotation about the desired axis.
Then no tool more precise than a disk or belt sander is needed. Rather than explaining all this, check out the information and photos in the eqplatforms group. However, my next page has details of the way I did this.
One small idea I had was to preserve the jig built to hold the Top Board during the shaping of the sectors. By driving the screws used to mount the jig and Top Board into the jig without the Top Board, and cutting off their heads so they can be placed back on the Top Board in the same alignment when used to shape the sectors.
When set into this position, it serves as a fixture for aligning the finished platform in the correct azimuth and elevation for polar alignment.