Wooden Compressor

by John

Another boring cannon post.

A very pleasant drive to Warrnambool yesterday, and re-inspection of the very rare compressor which was the recoil arrestor for the LowMoor 68pr cannon. And probably for all guns on the same carriage and platform, including the Armstrong 80pr RML’s at Elsternwick, Queenscliff, etc which I am currently modelling.

This is the 1861 compressor. 2 elm wood pieces, plus a repair on the right, all splits, cracks, rot and rust, and rather fragile. 4″ thick. Possibly the only one of its type still in existence. The central bronze elliptical bearing shell halves are in good condition. The iron pieces riveted to the bearing shells are rusted, but fairly intact. The rectangular pieces in the corners rest on the inclined platform slides. The central iron presumed elliptical post and its handle are missing.

I wanted to closely examine the iron riveted pieces closely to check my theory that the short straight sections are the parts which acted as the cams to close the gap between wooden leaves and release the friction from the braking action. Unfortunately the rust concealed any such evidence. But I still believe that was the purpose of these iron pieces.

So, today, I commenced making a 1:10 scale model of the compressor to fit to my miniature cannon.

The bronze bearings and attached iron cams protrude above the surface of the wooden leaves.

At 1:10 scale the bronze bearings would be less than 1mm thick. How to make them?

I CNC milled them from some gunmetal hex bar, then parted them from the bar in the lathe. I had previously made the wood leaves, and CNC’d the elliptical hole to fit the bearings. I don’t have any elliptical drill bits.
… and they fitted nicely. The original bearings were screwed to the wood leaves. I intend to use Loctite. The originals were made of elm. I used a close grained Victorian Mountain Ash.

I milled the steel elliptical post from silver steel. Yes, CNC’d.

Steel post, threaded to eventually fasten the handle with pins to move the cam pieces. Handle not yet made.
The pieces all fit well. The screw is temporary.

Another workshop session require to make the iron cams and the handle with pins.