Time to bite the bullet and glue the outer frame. When this is done the two parts of the outer frame will be attached forever, the metal bar to hang the spherical robot will be in place, and the o-ring channel will be smooth.

I started by printing a supporting jig into which I can bolt the two main frame pieces, holding them in place while the various glues dry.

I first glued some nylon pins into the ends of one frame piece (there are holes in both). This will aid alignment of the frame when assembled and improve its final rigidity. You can see the pin glued here:

The end of the frame has some more superglue applied. This is the first glue used to bond the two pieces of the frame together.

Here you see the frame, bolted into the jig, assembled and waiting for the glue to dry. While the two pieces mate well together, there are small gaps which I needed to fill. If I didn't, they'd provide a path for water to leak in later.

The gaps are filled using a syringe of the Formlabs Rigid resin. A little of this resin is injected into the gaps (and encouraged using a small paint brush). Then more resin is painted into the o-ring groove to make it smooth and continuous. The groove needs to be smooth otherwise water will wick between the o-ring and the surface. This additional resin also helps to two parts bond together (the second glue).

A blue/violet laser is used to cure the resin (which should only be used with the appropriate eye protection because this thing is nasty).

The final results looks like this: