johnsmachines

machines which I have made, am making, or intend to make, and some other stuff. If you find this site interesting, please leave a comment. I read every comment and respond to most. n.b. There is a list of my first 800 posts in my post of 17 June 2021, titled "800 Posts"

Tag: RML

Armstrong RML barrel

After 3D printing a plastic 1:10 barrel I decided to have a go at turning one in steel.  I had a length of steel 70mm diameter and 290mm long, which was just too short to turn the entire barrel, so I decided to make one of the breech reduction rings separately, when I make the cascabel.

I did not know what the steel grade was, but it was off a machine so I thought that there would be a good chance that it would be reasonable quality.

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The length of rod next to the printed barrel.

The turning was initially fairly routine.

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and I was really pleased with the finish which was appearing.

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Mountains of hot swarf.

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The roughed out barrel.  I used the 16mm drill bit to drill the bore from both ends, but there was still 50mm or so beyond the reach of the bit.  So I silver soldered the drill bit into a length of silver steel (drill rod).

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And quickly completed the drilled hole. 

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Then transferred the piece to the CNC lathe, and shaped the barrel exterior.

I experienced 2 problems with the CNC turning.  The tapered chase of the barrel, and the rounded fillets came out really well, but the straight sections of the breech developed chatter marks.  I was preparing to take a skim to remove the chatter marks when I bumped the manual CNC control, the cutter dug in, and I got a deep score in the breech.  And broke the carbide cutter.  I turned away the dig in, but it left the breech diameter 3.5mm undersize.

I have no more steel of that size, and it will be quite a while before I get an opportunity to buy some.  So I persisted with the slightly undersized barrel.  It will be 62mm diameter rather than the intended 65.5mm.   I still have not decided whether to scrap it and start again.  But if I can get some more suitable steel I will remake it.  I might even use the undersized barrel to make a 64lb Armstrong RML, which had a smaller diameter breech than the 80lb RML which I am making.  (note added 19 Jan 2021…  The Armstrong 64pd and 80pd barrels had the SAME dimensions.  The main difference was that the inner tube of the 64pd guns coiled iron, but in the 80pd guns was solid ended steel. “Naval Gunnery” Garbett pp52-53).

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I showed it to SWMBO.  “That is beautiful” she said, somewhat to my surprise, and being surprised by its 3.5kg weight. 

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Ah…  if only…

Armstrong RML

Some images of what I am planning to be my next model build.  As mentioned in a recent post, I photographed and took lots of measurements of this Rifled Muzzle Loader at Port Fairy, and have been searching the web for more information.  It is said to be an 80 pounder, but the bore (6.3″) is more consistent with a 64 pounder.  Can anyone shed any light on the discrepancy?

(note added 20/12/20…  I have now completed the model of this cannon.  See photo at end of this post.  To answer the question above, my reading indicates that the 6.3″ bore was used for both the 64lb AND 80lb cannons.  The 64/80lb refers to the weight of the projectile.  The Port Fairy cannon in the picture is indeed an 80 lb cannon.  The extra capacity of the projectile and the gunpowder charge was permitted by extra strength of the barrel provided by a more advanced construction method.)

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Yes, there will be some interesting machining challenges.

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Not looking forward to all of that riveting.  Considering options.

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Most of the photos were taken with a Panasonic Lumix camera, but some, like this one, were with my iphone, using an App named “My Measures” which accepts annotations and measurements.  The barrel “diameters” above are actually circumferences.  And the “19” is the plate thickness.

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The emblem on the barrel surface.  I am hoping to engrave this on the model, but there would be a lot of time cleaning up the image.

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A web search turned up this image, which will be easier to clean up for laser engraving on the model.

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And some basic diagrams of similar design

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The rifling grooves are 1″ wide.  3 of them.  How to make them?

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I asked about rifling grooves at a GSMEE meeting, and Rudi showed me how it is done.  He made these 2 rifling tools.   They are pushed through the bore to create the grooves.  The bottom tool was most succesful, because it has a pilot diameter.  But, the tools cannot be pulled backwards, so both ends of the bore must be open.  But what about the cascable end of the cannon.  It is not a breach loader.

Then the penny dropped…..I remembered seeing this diagram…

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The cascabel screws into the barrel.  That opening will allow me to broach the rifling.  I do not know how the rifling was made in 1866!  (does any reader have information on that point?)  Note also that these barrels were usually made with some concentric tubes of steel.  I expect that the model will be one piece of steel, with the trunnions silver soldered.

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And I have started drawing up the cannon, massaging the field measured dimensions (which were obtained with a builders’s tape measure)…

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And doing gear calculations for the gear train and rack.  Lots more detail to go into the drawing and plans.   And thinking about construction methods meanwhile.  Now who has a metal sintering 3D printer for loan?

See posts on this site throughout 2020 for construction of the model….

 

 

The completed model at 1:10 scale.