Had to work out some the functions on this build her:
1) A secure verticle post.
2) A bar with a stop block
3) A indexing system
4) A locking system

The Post (#1): this one may be a tad bit long, but always good to start up with extra. I used a drop of Oak stair tread that was in the shop and ripped it to 2". Thinking this will give me a good support system for the bar that needs to extend to the center of the turntable. Now I needed a block to hold a bar in place and yet be able to slide up and down on the post. Again, over to the scrap drawer of Oak, and dig out a few blocks. Had to have something to go across each flat and each short side, so a combination of 3/4" and 1" stock was chosen.

I formed a hollow box to wrap the post, just used but joints for this and glue only. The Bar (#2) had to be installed so that it rides against the side of the post. Over to the table saw and cut a shallow dado for the bar, after a little fine tuning with chisels and a file had a good fit with the aluminum bar stock (yea it a little long for now) and the post. Now time for a glue up, that High Vise came in handy for an extra set of hands.

And an assembly.

The stop block was easy, just ran it through the table saw centering the grove. Both blocks will have a thumb screw taped into them.

Back the post now, had to have something that will make this secure and plumb. I decided it would be a good idea to build a frame around the base for that and the other mechanical parts that are in the requirements, (more on that later). So, in order to attach the post in the corner of the jig, also to match the layout lines being at 90* to each other. A short shoulder was cut at the base of the post, then notched 45* from the center, (missed the photo). Then a block was cut to go across the edge opposite the corner, spanning the frame, this block also has a shallow dado to lock the post in place. When the post is installed, I will drive 3 screws in, 2 from the outside of the frame and 1 from inside through the support block.

A good solid connection and the bar is parallel to the turntable.

The Indexing System (#3): I ordered a full circle protractor which is 12" diameter to sit on top of the turntable. So, I had to install a block across the corner of the frame to support a piece of acrylic with a index mark. this is a simple one, not sure of the height yet (waiting for deliver). I just may cut it flush with the frame and add a block to get the height of the index plate.

The locking system (#4): Started thinking again, might not be a bad idea to be able to lock the turntable while gluing a segment in place. So again cut a block to go across the corner of the frame, so it would just clear the turntable. This was part of the reason to have two layers between the base and the top, needed a tad bit of room to allow for a lock pin.

Originally, I was going to use a threaded coupler, but the hardware store was out. Looking around the parts, I chose to use a T-Nut. Was thinking a longer thread should be used to keep the threaded rod going in straight to push up against the bottom layer of the turntable. The T-Nut will work out, and the little tangs give it a tad bit more support (it will be epoxied too). The was counter bored then the through hole for the threaded rod. Currently this is a 1/4-20 hex bolt, may or may not increase the size a tad to a 5/16-18, not sure yet. However, it only needs to lightly hold the turntable in place. I will lock a wing nut at the end up against the hex head, so wrenches are not needed. Engineering as I go along.

Oh, that frame was also needed because of the 1/2" block of plywood at the bottom of the round cylinder. There is a shallow dado on the inside of a 1x4 stock to allow clearance for that block. And the frame will allow a good secure connection for all of the mechanics needed to make this thing work.

One note to add that base is not exactly square, 16-1/2" x 15-3/4", it's what I had. But it works out with the 90* layout lines having the one for the post not going directly into the corner.

Thanks for reading and following along, comments are always welcome and appreciated.