Armstrong RML Cannon Sights

by John

The sights were the final parts to be made for the model Armstrong RML.

There were reasons for delaying these items. They are tiny, easily dropped and lost, have tiny almost invisible details (to my eyes), and involve fine and very deep drilling into the barrel, on which many hours have previously been expended.

First I looked up every reference I could find about the full size originals. I could find no picture of the sights on the 80pr Armstrong, but I did find some diagrams of the sights on the Armstrong 64pr, on which the 80pr was based. Another problem was that there were rapid developments in sight technology, and I had to decide which period I would choose. The later periods (after 1880) had complexities which did not exist in 1860. In the end I just made decisions, knowing that they might not be exactly correct, but thinking that if further information surfaces I could make and install new sights.

This is the design I chose. The 64 pr had 3 pairs of sights, the 80 pr had only one pair, on the right hand side.

The next step was to drill some 2mm and 3mm holes into the barrel.

The drilling setup. The barrel was held firmly between brass strips. The breech end of the barrel might need a bit more finishing.

First I milled 3mm flats. The first milling bit, solid carbide, just snapped as it bit into the barrel from the side. A HSS bit was more long lived.

A complication was that the foresight was vertical, but the hindsight was sloped 2º inwards to adjust for slight lateral deviation of the projectile which results from the rifling.

Next, a 2mm hole was drilled right through the barrel, missing the bore, and exiting through the bronze bracket which supports the elevation quadrant gear. At 40mm deep that hole qualifies as deep drilling. Tension drilling.

I did not have a long series 2mm drill bit, so I silver soldered an extension, leaving 40mm of the 2mm bit exposed. No photos of the deep drilling. I had other things on which to concentrate. The drilling was actually uneventful.

Showing the drill sitting in the hole
Fabricating the sights involved silver soldering 0.5mm brass strip to 2mm stainless steel rod. This was the soldering setup. The the sights were shaped by belt sanding and filing.

And now for some sights of the sights on site.

I will polish the sights.
Apart from dusting the base, and some final polishing, the model Armstrong cannon is now completed.