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.

Tag: RML cannon

How were Trunnions Joined to 1866 Barrels? Correction of a previous post.

The earliest cast cannon barrels were cast in one piece, and the trunnions were included in the casting.

By 1866 however, large barrels were made from 4 or more separate pieces, which were heat shrunk together, and additionally forge welded together.

The following information comes from “Naval Gunnery” by Captain H. Garbett, published in 1897.

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The diagram is of a 64lb Armstrong rifled muzzle loader.  The 80 lb muzzle loader, which I am modelling, was very similar to, and based on the 64lb gun, except that the diameters of the sections were larger, giving greater wall thickness.

The “A” tube, containing the bore,  was made from best quality forged steel, in one piece, although earlier models used the “coil” method described below, and earlier than that it was wrought iron.  It was permanently closed at the breech, but in slightly later models it was open, sealed with a copper disk which was held against the cascabel.  The A tube was bored and rifled after assembly of all of the barrel pieces.

The “B” tube, or tapered chase was heat shrunk onto the “A” tube.  It was a coil construction. (see below).

The “Breech Coil” had 3 components, plus a cascable which screwed into place with a deep, asymmetric thread.  One of the components was the “trunnion ring”, which was welded to, and separated the other 2 components.

“COIL” TUBES.

When steel is forged into a strip, apparently it is strongest along its length due to the orientation of the crystalline structure.   It was discovered that the strongest cannon barrels were made from long strips of forged iron or steel (up to 200 feet long), which were then wound around a mandrel, while red hot, forming a cylinder.  The red hot coil was then hammer welded into a solid cylindrical mass, with most of the steel crystals aligned circumferentially.  It was then machined into its final shape, with allowance for final heat shrinkage onto its mates.

 

The “TRUNNION RING”.

The trunnion ring was forged from a single billet of steel.  Two holes were punched through the red hot billet, expanding the sides.  Further hammering shaped the trunnions from the lateral expansions.  The final shape was then machined.

The three breech pieces were forge welded together, and heat shrunk onto the “A” tube and the “B” tube.  I could not discover the construction sequence of welding/shrinking these components.

This post is to correct an earlier post about the trunnions in the Armstrong cannon  construction, in which I stated that the trunnions were heat shrunk into the barrel.  The incorrect implication was that the trunnions were heat shrunk into holes in the barrel sides.  My recent reading indicated that the “trunnion holes” method, which I used in my model, was NOT the method used in 1866.  I am not losing sleep over this lack of authenticity in construction of my model.  One of many compromises which are made when scale modelling.

 

 

Lost PLA Casting – 3rd pour

Today I attempted another aluminium casting session with trees that I had made 2 days ago.  More wheel forks, and barrel trolley brackets.  16 parts altogether.

And this time I installed air release vents, following my previous poor results, and at the suggestion of reader Rob R.

I also made some 50mm extensions of the pouring funnel, to increase the head of melt pressure.  The extensions were “add ons” rather than designed into the system, and the molten aluminium leaked between the extension and the main flask with the tree, so I doubt that they were very effective.

BUT!  Of the 16 parts on the trees, 14 were good to excellent, and only 2 showed any voids, and I assess one of those as repairable.  So, 15/16 is very pleasing.  I feel that I am closer to getting good results every time, if I can make an effective system of increasing the delivery pressure of the molten aluminium.

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These are the extension pieces to the funnels on the investment flasks.  The shape was made with the plastic funnel.  If I had positioned them before the investment plaster had set hard they might have worked better, but as they just sat on top of the already hardened plaster, the join leaked molten aluminium rather badly.  I have a different system in mind for my next pour.

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Previous failures were cut up and thrown into the melt.

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See the tiny silver dots surrounding the central funnel.  That proves that the air vents functioned as intended.

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The aluminium trees.  Not very pretty, but delightful to see.  10 parts on the top one, 6 on the other.  It is odd to see the wax spaghetti turn into aluminium spaghetti.   I will separate the parts tomorrow.

And while the investment burnout and baking was proceeding, I worked on previously cast parts.

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The centre columns have beep painted with etch primer.  A little more filling required, then I will use the best 2 on the models.   The 2 bracket and column assemblies on the right were initially considered unusable due to large voids, but I used some aluminium solder to fill the defects, and they might possibly be OK.  The 2 on the left just need some tidying, machining removal of  melt tubes, and minimal filling.

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I will probably remake this one, but will continue to salvage it and see how well it comes up.  Note the solder fill on the RHS.   That will not be seen on the model.

One more melt and pour, and that should be the last of the castings made for the model Armstrong cannons.  It has been a challenge, and lots to learn, but very interesting and very satisfying.

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Finally for today’s post…  I noticed some black marks on the normally pristine white wall above the casting bench.  They extend about 4 meters above the floor.  Do you know what they are?  The paint has been melted off the wall by bits of flying molten brass, resulting from the steam explosion 2 days ago!

Many thanks to Rob R for his spot on suggestion about the air vents.

Video of Casting Small Complex Cannon Parts

This video was taken and edited by my daughter Eleanor.  I was doing an aluminium pour of some parts for the Armstrong RML cannon, explaining the process to her.  I was hardly aware that she was videoing, so the interaction is conversational.

Although the pour was not a success because none of the parts were good enough to use, it does show the process as seen by someone who previously knew nothing about it.

 

 

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There is also a 20 minute video of the whole process which I will add to this post when it is available.

Reader Rob has suggested that the positions of the defects suggests that air entrapment is the cause of the voids and that the fix is to position some vents at the positions at risk.  I will try that with my next pour.  Thanks Rob.

Here is the 22 minute video.  Just as recorded.  Not planned or edited.

 

 

 

 

 

 

 

Armstrong Cannon Wheel Assemblies -2

rear wheel and support

There are 3 major components of each wheel assembly, plus the wheel, axle, and king pin.

The wheels, axles and king pins are straight forward metal turning, but the other 3, the wheel bracket, the king pin post, and the chassis bracket, are castings in the original.

For my 1:10 model I am planning to cast the king pin column, and the wheel bracket.  But I will fabricate the chassis brackets.

There is one chassis bracket for each of the 4 chassis wheels, and they are all different.  Front different from rear, left and right hand versions.  And each one has angles of 90º, 30º, 20º, 6º, 2º so the machining was quite a mental exercise.  No major stuff ups though.

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Here is the main component of the left hand rear chassis bracket, being held in position.  It will be bolted on later, and have several flanges silver soldered to it.   Those M2 cap screws will be replaced by rivets eventually.

Meanwhile, having decided to cast the king pin casing, and the wheel bracket, I spent many pleasant hours (or was it days?), drawing them.  Then yesterday, I 3D printed an example of the king pin casings.

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2.5 hours to print PLA examples of rear (left) and front king pin casings.  I need to see the original cannon to check some details before committing to cast these in bronze.  The PLA parts will disappear during during the casting process.  (A pity.  They are quite attractive No?)  You can see why I chose not to machine them out of bar stock.   3 pin holes in the left hand print ? the result of not storing the PLA spool in a dehumidified container.

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So, it might not look like several days of computer and workshop time, but that is how long it has taken.

In Australia we have had some easing of Covid-19 restrictions, but not opening of museums or historic collections of cannons.  So I still cannot go to Warnambool (a 2.5 hour drive) to check details on their Armstrong 80 pounder rifled muzzle loader.  Flagstaff Hill Maritime Museum does not answer their phone.  Hmmm.  Maybe I could climb the fence and sneak in……    but maybe not.

Armstrong Cannon Chassis Wheel Assemblies

The steel chassis is virtually finished, although I am delaying inserting the final rivets which join the girders together, in case I need access to the individual girders for more machining or drilling.

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The 2 chassis’ are not identical.  Can you spot the differences?  And still waiting for more rivets to arrive.  The copper colour on the front one resulted from dipping it in well used sulphuric acid after some silver soldering.

 

Considering how to model these wheel assemblies…..

front wheel and mounts

The front wheel assemblies

rear wheel and support

The rear wheel assemblies

The rear wheels and supports are larger than the front ones.  But the top views are essentially the same.  The wheels themselves present no difficulties.  They will be turned from 50mm diameter steel rod.  And the axles will be all identical.

But, those supports are complex, and will need to be silver soldered parts, or possibly cast from 3D printed lost PLA bronze or brass.  Just drawing them was challenging.

This is a complex project, and the parts are complex.

Considering that the original cannon barrel was made in 1866, and the steel/iron chassis made approximately 20 years later (the original barrels were mounted in a wooden carriage),  the standard of the workmanship in the originals is simply superb.   Even at 1:10 scale, and using modern equipment including CNC machinery, I am struggling to match the standard of fitting steel pieces together so neatly.  I am in awe of the original engineers.

(and by the way.  Neil M, who very kindly loaned me the rivet gun which died, has loaned me a replacement gun.  The replacement gun is a bit bigger, and more fierce.  It requires more care in not overdoing the hammering, and bending the steel parts or producing “two-bobs” in the work piece.  “Two-bobs” will be understood only by older Aussies?  They are unintended dents in the workpiece produced by hammering.)

Model Cannon Barrel. (T)rifling Thoughts.

My aim (as it were) in making this model cannon is to have a high visual quality exhibition piece.

It is a 1:10 scale model, 1866 Armstrong 80lb, rifled muzzle loader, blackpowder cannon.

One question which always arises is whether it will be actually fired.  My answer is that if it could be fired legally, it would be nice so I could make a video.  However, Australia has very strict gun control laws, (with which I totally agree), and I do not intend to flout those laws.  So this gun will not be capable of being fired.  It will have no touch hole.

To satisfy the visual appearance of a touch hole there will be a laser printed dot at the location.  Along with laser engraved Queen Victoria insignia, sight lines, etc.

But, it IS a rifled cannon, so I do intend to rifle the barrel.  And that needs to accomplished before the trunnions are fitted, and after the cascabel is fitted, so the orientation of the rifling is as per the original.

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The original rifling.  The 3 grooves are each 30mm wide, (clockwise or anticlockwise, not sure) and extend up to the edge of the powder chamber.  They are about 2 mm deep.  The powder chamber is slightly wider than the barrel bore, being continuous with the depth of the rifling grooves.  It is academic, because it will not be visible, but I will make it (the powder chamber, and the whole model) as accurately as I can, for my own satisfaction.  Fortunately the powder chamber is accessible to machining from the breech end, because the cascabel is screwed into position, and is removable.

Yesterday I started making the cascabel.  It was difficult.  The steel thread is lathe cut first, then the shape is lathe CNC’d.  Then there is milling the insides, and making a removable pinned rope retainer.  The third attempt was the most successful, but I am still not satisfied, and so there will be another one made today.   This is what I have so far…

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The turned barrel, threaded to accept the cascabel.  More work is required on the cascabel.

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The cascabel is mounted in an ER40 chuck.  It has been drilled and milled, and a removable insert is temporarily glued into place pending more machining.

 

Rifling.  Searching YouTube reveals multiple tools and setups from US sites.  Here are a few screen shots to show you some varieties.

From the sublime ….

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to the other extreme…

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No.  I will not be using a PVC pipe lash up.

The amateur designed and built machines are interesting….

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Sine bar on the right.

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Then there is the method of pressing a button cutter through the bore.  My bore is an odd size, so if I used this method I would need to make my own cutter.

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This one is a computer animation of a 19th century rifling machine, now a museum exhibit.   Can you see the barrel?   Armstrong probably used a much larger version of this type to rifle his cannons.

 

But I think that I will use none of these methods.  I have a CNC mill and a CNC rotary table.  Mach3 can control both of these machines simultaneously.   If I mount the cutter assembly in the rotary table, and the cannon barrel to the mill quill, I should be able to cut the rifling grooves.  Still working on this one.

Armstrong RML. Roughing Out the Barrel

Today was humid.  But I hardly noticed.  I was attacking a piece of 72mm diameter steel rod for the Armstrong 80lb model cannon barrel.   Enough of the plastic printed shit.  Now for the real material..

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It was a piece of an axle.  No idea of the exact material.  But it is magnetic, turned beautifully.  So not stainless.

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The roughed blank, and the plastic printed model.

Next problem was to produce the 16mm bore, through 285mm.

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None of my 5/8″ (15.87mm) or 16mm drill bits were long enough, so I drilled from both ends.  Still have a substantial chunk in the middle.  The cutting fluid is my own mixture of olive oil and kerosene.   I used to grow and make olive oil and I have quite a bit left over.

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The roughed barrel, ready for CNC finishing.  And a 16mm drill bit which I turned down to a 10mm shank, and a piece of 5/8″ drill rod/silver steel drilled to 10mm, which I will silver solder to the drill bit to make it adequately long to drill through the whole barrel tomorrow.

 

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The roughed barrel, and the 16mm drill bit ready for silver soldering.  Yeah.  It is a bit longer than necessary.

Turning cannon barrels is really satisfying.  Still considering how to manage the rifling.

BTW.  I am not feeling the love lately.  If you want these posts to continue, you need to hit the “like” button occasionally, or better still, make a comment.  If I continue to feel unappreciated I will just stop.

3D Printing a Cannon Barrel

There is quite a learning curve to 3D printing, and most of my prints so far have exhibited considerable room for improvement.  There are some helpful YouTube videos on the subject, but at my beginners level there is still a lot of trial and error.

I am still planning my next cannon model build, and printed some cannon barrels to improve my printing skills, and also to have a plastic model of the barrel to help decide about construction methods of the metal model.

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This is a 1:20 print, but was unsatisfactory because the cascable, and the rifling did not print.

The next prints took 22 hours (vertical orientation) and 24 hours (horizontal orientation) each.

Firstly the vertical orientation..

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It starts with a thin line which marks a little beyond the outside outline of the model to ensure that it is properly located on the printing plate.  Then a thin base to ensure adherence of the model to the printing plate, for the duration of the printing.  My plate is heated to 60ºc, which is not essential with the PLA filament which I am using.  I changed the filament colour for aesthetic reasons.

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Each layer of filament adds another 0.2mm of height.  The rectangular columns support the overhanging parts, and increase the overall support of the model during printing.

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The printing is finished after 22 hours.  I can already see some mistakes.  The barrel should be smoothly rounded, instead of faceted.

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After breaking off the supports.  Next to a bit of workshop rod  which I will use to make the actual cannon model.   Not quite long enough, but the rifled gun tube and cascabel will be made separately so the steel rod will be long enough for the rest of the cannon.

The next print was horizontal…

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I made the supports more densely placed to improve the support.  The cannon barrel is just appearing in the centre.

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I left the printer to continue overnight, and this is what I saw next morning.  Note the longitudinal placement of the plastic fibres.  Infill set at only 3%, which was adequate.  I increased the outside wall thickness to 5 layers, which was plenty thick enough.

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The finished horizontal print on its supports (front) and the vertical version (behind).   Apart from the facets, the appearance of the vertical version was better IMO.

Now I am ready to turn the barrel in steel.  I have obtained a facsimile book about naval artillery which was written in the late 19th century, it reveals that the Armstrong barrels were made in concentric pieces, and heat shrunk together.  I will adopt a similar method, making the cascabel and the central rifled tube separately from the breech sections.   Not decided whether to heat shrink them together, or silver solder, or Loctite. (ps. a week later.  Changed my mind.  Making the barrel from a single piece of steel)

The artillery book also answered my question about 64 -80 lb cannon and bore sizes.  When round shot was replaced by pointy cylindrical projectiles, the projectile weight could increase by increasing the length rather than the diameter of the projectile.  And some 64lb cannons were redesignated as 80 lb cannons, after modifications which did not necessarily alter the bore.  Unfortunately the book does not answer how the rifling was accomplished with a closed breech.

And I made another workshop tool.   This one is a lathe tool height gauge.

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I expect that the tough PLA will stand up to workshop treatment quite well.  It is light, very visible, will test upright and upside down tool bits, and will hang on a conveniently placed hook. Also, it is within 0.01mm of the required 38.05mm tool height.  A light rub of the base over fine emery paper will get the dimension right on.