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Tag: trunnions

Armstrong RML Cannon Trunnions – 2

Silver soldering the trunnions into the barrel and the squared blocks did not go well.

For a start, I did not know the composition of the steel of the barrel.  The trunnions were/are silver steel, and the blocks were mild steel.  So it is possible that I did not use the best flux.

And the barrel is quite hefty, so I knew that it would require a lot of heat to get it to temperature, and to keep it at soldering temperature.  So I used a large oxy-propane torch, and heated it to dull red heat.

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The steel pieces fluxed and wired together, ready for heating

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It was a cool day, but the heat output from the red hot barrel was ferocious.

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Soldered, but one side was not good, and a hammer blow dislodged it.  Damn.

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The good side, partially machined.

I dithered about how to deal with the faulty side.  I was not enthusiastic about re-soldering it, expecting that the good side would fall apart.

So I cleaned up the pieces, and used high strength, high temperature, Loctite 620, to join the pieces.  The machining will test the strength of the joins, so I will give it the full 24 hours before testing it.  This is the “reject” barrel.

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Still pondering how to join the trunnions of the “good” barrel (front).  I will discuss it with my colleagues tomorrow when we have a Model Engineering Society meeting on “Zoom” video link.  The 3D printed barrel at back is a handy “how it should look” example.

 

 

 

Armstrong RML Cannon Trunnions 1.

cannon from above front

The 80lb Armstrong RML cannon trunnions were probably heat shrunk into the sides of the barrel.  The squared off barrel sides would have been part of the original wound and welded steel rods, and machined to shape before the trunnions were inserted.

The hole above the trunnion is to hold one of the 4 sights.

For the 1:10 model I considered various construction methods. This is what I decided…

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The 20mm diameter trunnion is fitted into a milled steel block, and the 2 pieces on each side are then silver soldered into prepared recesses in the barrel.

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The the barrel is mounted in the CNC rotary table and tailstock.  15mm deep holes are drilled into the barrel….

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and widened to 20mm diameter (drilled then milled)……  (for cutting fluid I use a mixture of olive oil and kerosene.  It produces a lot of evaporated fluid but is very effective at keeping the job cool).

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….then complete the recess.   The bottom of the recess is 8mm clear of the bore.

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Next step is to make the blocks, the trunnions, and silver solder them all together.  Not entirely authentic, but compromises are required when scaling down.   Still on the reject barrel, as a trial run.

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