To give some perspective, the entire chamber assembly above is about 4 inches tall. The lower portion is about 4 inches diameter on the outside.

The view on the left is a close up of the bottom of the sample holder that is inserted in the top chamber. It extends into the lower chamber. The central hole stops just short of the bottom and is only about 3/32 inch in diameter.

The lower view shows three holes that closely surround the sample holder. These give the temperature controlling liquid a path between the two chambers as close to the sample holder as possible.

If any of you have machined Plexiglas, you will understand the challenges here. The cutting tools must cut as freely as possible to keep heat from building up. Just a small excess of heat will lead to microscopic cracks forming and the possible failure of the part.

This is why I took the extra time to make the boring tool shown below. It is a tooth of a broken HSS reamer welded to a couple of CRS scraps. The cutting edge was put on with a small grinding wheel in a hand held die grinder. The scooped out shape allows the cutting edge to peel off material like a knife.

Not the least bit pretty - but quite effective!