Smith’s Screw -1

This is my CAD drawing of a Smith’s screw, which was used for fine adjustment of the barrel elevation of cannons on wooden carriage/platforms. The pivoting nut sits in the base. The threaded shaft is turned by the cog near the top which is turned with the iron lever which has protruding pins.

I started this mechanism for the Armstrong 80pr gun model today, by making the bronze base.

There were 4 components of the base, which were joined with silver solder. I could have printed the whole base and cast it in bronze, but I had nothing else to cast so decided to fabricate it with basic machining.

The 4 components. The bearing surface is bronze, the rest are of brass.
Squared up a lump of bronze, then used a ball nose cutter to make the rounded channel.
Carved out the desired bit…
And silver soldered the 4 components. Not very pretty at this point.
But with some filing and sanding it finished looking quite respectable.

Then to machine a recess in the posterior transom.

I did not want to make a mistake here, so did an air cut to test the CNC programming. First a shallow cylinder, then a deeper rectangular hole.
I spent an hour or so filing the part to make it fit into the recess. It was a neat fit, so pressed it into position.
A match to hold the “iron” quoin support in position for the photo.

Next session to make the cylindrical nut with a 5mm acme thread, and the matching threaded post.

I have made an appointment to see the original compressor unit at Warrnambool in a week, so I am deferring making that final component until I have checked some dimensions.