So, the first model Armstrong 80lb RML is finished. Final photographs following. I admit that some artistic license has been taken, as directed by SWMBO, and some scale details have been modified slightly in order that it is finished in time for Xmas.
Yesterday I fished out the components of the other model cannon, the “A” version, which I am making for myself, and which will be used in model engineering exhibitions. I predict that it will take another 2-3 months to complete. I am intending that it will be more rigorously an authentic scale model, and probably less pretty and decorative than the version pictured below. But it will look interesting alongside the 24lb long gun of the Nelson era, the 32lb carronade, and the huge Ottoman 1465 bombard, all to 1:10 scale.
Here are the final photographs of the “artistic” B version.
When I make the sights for my “A” model, I will also make some for this one.
There is a name plate which was lasered by my colleague Stuart Tankard but that reveals a bit too much information to show here. Suffice to say, it names the cannon, a few basics specs, maker’s name, and year. It will be fastened to the wooden base. It also states “NEVER FIRED IN ANGER”.
Thankyou to all of my readers, many who have supplied useful advice and welcome encouragement. Particular thanks to Stuart Tankard for his lasering expertise and machine, and other technical advice. And thanks to SWMBO, who has warmed to this project as it approached completion, despite having absolutely no interest in weapons of destruction. She does have a good eye for form and colour. And mostly for putting up with my foul moods when things went wrong.
Now. It will be interesting to see if the recipients of this model actually like it.
I have machined a wooden base and I will fasten the central column of the cannon chassis to the base. The reason is that people cannot resist swivelling the cannon around on its column and the the wheels tend to mark/scratch polished surfaces. Better to mark a wooden base than a polished mantelpiece. But how to finish the surface of the base? Any polish/paint will quickly develop marks from the wheels. I have decided against making steel railway lines for this model.
I have used an Australian hardwood (mountain ash, a very hard dense wood, reclaimed from a demolished building). I am thinking that I will just oil it. The colour of the wood will darken with age, but will never be as dark as the table, which I made decades ago from Australian Iron Wood. (note, not iron bark. Iron wood. The hardest, densest wood I have ever used. And yes, I have worked with lignum vitae, and Australian red gum. The marks in the surface of the table are only in the polish. The wood is almost impossible to scratch. My kids used to dance on this table 30 years ago.)
The burn mark on the end of the base is from the belt sander. I will remove it with hand sanding before oiling.
The machined finger grips on the ends were made on my vertical mill with a steel moulding cutter intended for metal machining. It worked well.
I discussed the finish which I wanted to achieve with my resident finishes expert. SWMBO. I wanted a slightly darker, low sheen finish, which would not get scraped off with the cannon wheels.
She recommended this stuff. It is a stained, penetrating oil. Smells very chemically.
It is actually a surface repairer, rather than an overall finish but I did what I was told.
OK. That looks good. The surface will be easy to touch up if required.
1:10 Model Armstrong rifled muzzle loading 80lb cannon WILL be ready for Xmas.
Apart from minor touch-ups, the model and painting is completed.
I will take some careful photos before it goes to its final home, but here are a few snaps to show how it appears with some paint and lacquer.
So, was SWMBO correct about not painting the chassis? I like the look of this finish scheme, but now have to decide what to do in that regard with the “A” model, which was put aside while I finished this one.
p.s. I weighed the model, because I was curious. The full size original barrel weighed 81.5cwt/4.1 tons plus the carriage/chassis, about 5 tons/5080kg total. The 1:10 scale model should weigh 0.1 x 0.1 x 0.1 or 1/1000th of that which would be 5kg/11lbs. It actually weighs a tad under 10kg/22lbs which is almost exactly double the predicted. It is a bit of a lump to carry around and I do NOT know where the extra weight came from. Or maybe my mathematical assumptions are incorrect.
The accuracy of cannons was dramatically improved in the 19th century with several developments.
The bore was machined rather than just cast, as result of the invention by Wilkinson of a powered boring machine. Incidentally, this process was also adopted by Trevithick in making steam engine cylinders, significantly improving the efficiency of steam engines.
The adoption of sights, calibrated for distance, and movement of the target, instead of just eye balling along the barrel.
Changing from round iron balls to cylindrical projectiles, with a pointy front and slightly rounded rear.
Rifling the barrel bore, causing the projectile to rotate.
Standardising the weight and granularity of the blackpowder, making shots more repeatable.
Increasing the power of gunpowder by increasing the size of the “corns” which sped up the rate of combustion. This permitted flatter, more accurate trajectories.
Improvements and calibration of degrees of barrel angulation.
Increased research and knowledge of the science of ballistics.
Increased training and professionalisation of gun crews.
The Armstrong 80lb rifled muzzle loader had a projectile which weighed, you guessed it, 80lb (36kg). A bit later cannons were categorised by the weight of the barrel. e.g., the 80lb Armstrong would have been named a 4 ton cannon. The gunpowder was standardised at 20lb per firing. The gunpowder filled silk bag, then the 80lb projectile were manually lifted onto the loader cradle, then ram rodded into position. Later, bigger cannons, needed a small crane to do the lifting, but in 1866, the 25 Armstrong 80lb cannons which were made specially for Victoria and South Australia, and were the most advanced cannons made at that time, required strong gunners to do the lifting and ramming.
My model Armstrong cannon is basically a display, rather than a working (firing) model. So, for the display, I have made some projectiles, and fake gunpowder bags. I was fortunate to find some old diagrams of both.
As you can see, for an 80lb RML cannon, the projectile is 15″ / 380mm long, and just under 6.3″ diameter. The barrel bore is 6.3″ diameter, and to cope with heat expansion the projectile must have some “windage” (a gap) to avoid jamming. The 1866 projectile has a pointy end, and a rounded rear, which is relatively aerodynamic, and similar to the form used in many modern guns.
Attached to the rear of the projectile is a (dark shaded) copper disk, which expands into the rifling grooves after firing, and further reduces the windage, and causes the projectile to rotate. The copper disk separates from the projectile after they leave the barrel, and it falls to earth. The best examples of the copper “gas checks” have been retrieved from the sea, in front of shore batteries where these cannons were located.
Before gas checks were introduced, the projectiles had copper studs attached to their exterior. The studs fitted into the rifling grooves. The studs were effective at causing the projectile to spin, but they caused rapid wear of the cannon barrel, excessive drag and lower muzzle velocity of the projectile, and were slower to load. The 25 Victorian Armstrong 80lb RML cannons were designed so that studded projectiles could NOT be used. (n.b. note added 7 Jan 2021… that last sentence is incorrect. The 80lb RML’s would have used studded projectiles until mid 1880’s, and then changed to gas check projectiles. instructions were issued then that studded projectiles should not be used.)
The following drawing shows a silk bag, containing the gunpowder. It also shows the central wooden rod which prevented the bag from bursting during ramming. This powder charge is for a 10″ RML, so it is bigger and heavier than the one for the Armstrong 6.3″ RML, but the design is essentially the same.
After loading and aiming, the gunner would perforate the silk bag with a long spike, then insert a quill or later a copper tube, full of fine gunpowder which extended through the vent from the touch hole to the perforated silk bag. Royal Gun Factory experiments showed that the best firings occurred if the silk bag was perforated about half way along the cylindrical bag, so the vent and touch hole were located at that point.
The method of igniting the gunpowder will be described in a future post.
First, I have decided to NOT rivet the final joins of the chassis. Instead I am using dome head stainless steel bolts and nuts. The main reason is that the other end of the rivets are in impossibly small (for me) cavities and spaces, and I could predict that the final riveting result would be horrible. Even using threaded rivets would be incredibly difficult. This decision does cause me to reflect on the 1866 cannon builders who managed such perfect results with red hot rivets in confined spaces, and again, to be awed.
To divert, back to the painting.
Question. When painting a model, is it best to assemble the whole model then paint, or to completely disassemble every part, paint the parts then reassemble?
1. Disassemble and paint the parts then reassemble. This results in complete paint coverage of all parts. It results in clean separation of different coloured parts. Mistakes involve limited areas and are easier to correct. However, the thickness of the paint can alter carefully machined tolerances. And surfaces can be painted which were intended to be unpainted.
2. Assemble the entire model, then paint. This can make some recesses, corners and hidden areas difficult to access. But the appearance of the entire model can be assessed as the painting progresses, and major mistakes in colour choice can be corrected. The painting process does not alter dimensions or fitting together of components. But paint edges and joins can be difficult to keep neat and straight, particularly in my inexpert hands.
3. (Obviously what I chose to do). Partial assembly, into modules, then paint the modules separately. This has the advantages of both 1 and 2. The modules can be stacked together to periodically assess the results. The modules are smaller than the complete model, and easier to handle. Difficult decisions regarding colour, or whether to paint at all, can be deferred until the easier parts are painted, and some idea of appearance ascertained progressively.
So that is what I am doing. I have painted the bottom part of the chassis, and the carriage. Etch primer at this time, but already firming up ideas about final colour. And my colour and design expert advisor (SWMBO) has had some input into this decision.
At this stage, I asked for advice from SWMBO. She has suggested that the primed modules should be painted satin black, which should contrast nicely with the brass/bronze components. Avoiding gloss will minimise the finishing defects. Some filling of defects will be required in any case. The black colour will be tested on the carriage, and if it looks OK, the chassis subframe will receive the same colour.
SWMBO’s most interesting suggestion is to NOT paint the main chassis beams at all! Well, a clear lacquer will be required to prevent rust.
But. What about disguising the copper rivets/stainless bolts?
SWMBO: “they look interesting. Leave them.”
Me: “but, but, but, they do not look authentic.”
SWMBO: “This has to look like a work of art, otherwise it will be just a boring dust gatherer.”
Then I fitted the bracket which restrains the movements of the elevation gear lock-release…
So those are the last major parts to be fitted to the cannon. Oops. I forgot. I need to make the aiming sights, and bore the holes in the barrel to hold them. None of the cannons which I have inspected have exisiting sights, presumably stolen-souvenired, but some 19th century publications have good diagrams which I will be able use to make scaled versions.
I will add a rear wooden platform, and the eye bolts.
Then a complete teardown, painting some parts, polishing others.
It was a bit too warm for casting bronze today. 33ºc/91.4f. But I went ahead. It was sweaty.
I had installed a new thermocouple in the potters oven and it performed flawlessly. Fumes from burning out the PLA and wax from the mold had caused the older thermocouple to behave erratically, but the new stainless steel type was unaffected.
And, as I displayed yesterday, I had made a very ambitious tree with 32 parts to be cast, and a second tree with 2 largish parts.
No vents. No vacuuming of the melt. Just a straight pour.
So, a very successful pour. Some careful hand sawing required to cut off the parts.
After a session on the model cannon yesterday, I sat down at home with a glass of red and my laptop.
I was awakened by a phone call, but my bum was wet, and the laptop screen was black. And the laptop keyboard, and presumably my bum, was red with spilt wine.
Dealt quickly with the call. Dried myself off. Wiped the keyboard dry, but it was stained red.
Turned the Macbook on.
DUMB!!! Turn it OFF you idiot!!! I didn’t find that out until later.
Screen remained black. Charge cable light not registering.
Turned the laptop onto its edge and some wine dribbled out.
Still would not turn on. (See previous “DUMB” comment .)
Opened up another computer. Looked up “MacBook Pro Wine Spill” on YouTube. Lots of videos. Obviously I am not the only person to kill a laptop with red wine. Quickly viewed a couple of them.
“TURN OFF THE POWER”. “DO NOT TURN ON THE POWER”. Ok. Didn’t know that. Oh Dear.
“Use a 1.2mm Penta Lobe screwdriver and remove the back as soon as possible. The longer the delay, the worse the problems due to corrosion”
I have a few sets of tiny screwdrivers. None of them had a penta-lobe.
Rang around my computer savvy acquaintances, but none there either.
WHY DO COMPUTER DESIGNERS SPECIFY SUCH WEIRD SCREWDRIVERS?
Oh, I get it. They don’t want end users to fix their own computers. In a pandemic there is not much help from repairers either.
So, next morning I visited JayCar, and bought another set of tiny screwdrivers. They had a few sets with “penta-lobe” screwdrivers. This was the most comprehensive set. $AUD50. Really nicely made, bits held in multi layer case with magnets. Feels quality.
Removed the 10 tiny screws under a magnifying light.
Didn’t photograph the clean up steps. I was feeling very pessimistic about a successful outcome. Wiped off the red wine. But there was a sticky, syrupy, residue. A great glob of it under the big T shaped label, and a lot more around the vent holes on the right. I guess that the wine got access through those vent holes, and the keyboard.
One YT video showed a repairer scrubbing the electronics with alcohol and a toothbrush.
Oh well, here goes. So that it what I did, using methylated spirits. It felt risky, but the congealed mess did seem to clean off. Then I patted the cleaned areas dry.
Next question. Do I remove more components, to hunt for more areas of spill?
No. I think that I will try it first, just in case my cleanup so far has worked.
So I reassembled the bits which I had removed. Plugged in the power supply. … and the little power supply plug light came on! Hope!
Turned on the computer. Took a while to boot up. But boot up it did. Wonderful.
Next step. Make a complete backup of all of those files which I thought that I had lost.
Next step. Brag about my success on johnsmachines.com using the aforesaid MacBook Pro.
Meanwhile back to the scale model Armstrong cannon. The next photo shows yesterday’s result. Can’t see any change? Look carefully under the protractor. See that tiny bit?
That little piece represents several hours of cutting, silver soldering, filing, and fixing to the cross bar with TINY 10BA screws and nuts. Later it will have a mark to line up with the protractor marks.
So, life seems good again. And more Covid restrictions are being lifted tonight. Yippee. But still cannot see my Melbourne family for another 2 weeks.
BTW. I found some more videos to delete. So I have some more space for posts. But sad about the videos .
And the gears with ratchets attached need 2 mates. I tried to make them yesterday, but we had a wild day with thunderstorms and high winds, and my machines were playing up. I might get back to them today. (the ratchets can be seen in the header photo).
In country Victoria we are out of level 3 lockdown! Hooray! Still can’t see family from Melbourne, and minor restrictions on visiting local friends, and need to wear masks when out and about. But things are on the improve. I doubt that we have seen the last of the virus however.
I did not expect these mounts to require a third day session, and they are still not finished!
I discovered that two of the drilled holes in each bracket were in the wrong position, by approx 1mm. That is a really bothersome error, because the correct position includes half of the existing hole.
I managed the problem by threading the errant holes, and Loctite gluing in some threaded rod. Each rod was trimmed flush with the surfaces. Then drilling the new hole, partly through the Loctited metal patch. That fix worked well.
Threaded rod glued into the errant hole. Trimmed flush later. Then redrilled correctly.
THE TRUNNION PINS.
The pins hold the trunnion caps in place. And they took another whole day to make and install. Ah…. just as well I enjoy all of this. They are tiny, and I spent at least 50% of the time looking for them on the workshop floor after accidentally dropping them on several occasions.
Milling the pin handles from 2mm steel. The handles ended up at 7mm long. The holes were drilled before the outlines were cut. Then the tabs were ground off using my newly made belt sander belt. The belt lasted 15 minutes before the belt itself tore, with the join still intact!
Then some delicate silver soldering of a ring to attach a securing chain later, then the pin shaft itself. The wire through the ring is just to hold it in position during soldering.
And that is one of the 8 pins made. I will polish them in a gemstone tumbler next session.
On the model, the pins are jammed into position with a cam action, after some filing-shaping. On the original cannon there was a small protrusion on the inner end of the pin shaft, which fitted through a slot in the side of the carriage. I could not figure out a method of making such a tiny slot (1mm wide x 1mm deep) through 4mm of steel plus 2mm of brass, but the cam action seems effective. I will attach some chain soon, because I do not wish to make any more of these. And yes, the pins handles are slightly over-scaled, but I think not outlandishly so.
So, apart from polishing riveting and painting, I think that the trunnion mounts are finished.
Now planning to make the gear train for the carriage positioning on the chassis, and the pinion, quadrant gear, and bevel gears for the barrel elevation. We are currently in level 3 lockdown for Covid containment, with level 4 looking likely any day, so obtaining brass for the biggest gears is difficult. I am considering workarounds. Apparently community anxiety and depression, family violence, and even suicides are mounting. When I am in the workshop I am in a different world, thank goodness.
It took a whole day making and fitting the top caps of the trunnion mounts from brass.
A 76 x 76mm piece of brass was milled to 10mm thickness. The trunnion straps will finish at 9.5mm , giving me a 0.5mm machining allowance.
The 4 straps were cut out using a new 4mm endmill. Rounded internal corners were milled square, and the bottom tabs were milled to 2mm thickness.
2mm wide slots were milled into the brackets, and ends of the slots were filed square. None of my rifling files were small enough, so I ground one to size, leaving the faces and one edge intact.
Trunnion mount almost finished. Pins in the tags to come, and they will pull the strap down tight with a cam action. The half circle line on the bottom bearing is a painting border to delineate the bottom bracket from the bronze bearing surface which will not be painted. If you inspect the full size trunnion in the previous post you will see what I mean.
Now I can take some measurements of the model, and start the barrel elevating gear. There are 4 gears to be cut, including bevel gears, handle, shafts, gear case, and some complex mounts.
Back to the model Armstrong cannon carriage this afternoon, and fitting 2 internal transoms, which provide rigidity to the carriage.
The transoms had been laser cut some months ago. I cut the floor from 2.8mm stainless steel.
Each transom is attached to the sides and floor by angle iron, 2mm thick. In the original cannons the angle iron was mitred at the corners, and for this model “A” carriage I decided to try to replicate the mitres.
The angle iron was again bandsawn from RSS tube and milled to 10x10mm. I used the following setup to form the 45º angles…
This is the Eccentric Engineering tool sharpening arm, set up to 45º on my RadiusMaster belt sander, about to form mitre angles on the angle iron resting to the right.
The Angle iron pieces were glued to their respective transoms, and 2mm holes drilled. Bolts progressively inserted. The lengths and cutouts will be trimmed later.
Then milled and filed the corners until the parts fitted neatly into the carriage. Rivets will be inserted later.
…and for your interest/amusement, depending on your UFO opinion… Listen to the information, and try to ignore the appearance of the narrator.
….and do I think that UFO’s are real? I would say that my “belief” has risen from 95% to 99% YES. One of my readers, with whom I have spoken directly, and for whom I have no doubts about personal veracity, has seen one at close quarters. Do I think that they are of non human origin? A bit less positive about that one, but it does seem more likely than not. Waiting to see if and what NYT does publish.
Friction welding is a technique which is used in industry. It involves rotating 2 metal surfaces against each other, under considerable pressure. The heat generated from the friction is enough to make the contact surfaces to become red hot, then melt together. There is a funny and instructive YouTube video on the subject by AVE.
I had a costly and unintended demonstration of friction welding in my workshop yesterday. I was drilling multiple small holes in the 2mm thick sides of the model Armstrong cannon, when, somehow, I activated the Z axis downward in fast motion. Probably I miskeyed G0 instead of G1.
The hole was drilled in a fraction of a second and the chuck continued downward. My reflexes are not TOO bad, but by the time I hit the big red button, the bottom of the drill chuck was grinding into and bending the workpiece. Which was glowing red hot!
“Oh Dear”! (Or something along those lines.)
I could tell at a glance that the workpiece had been destroyed. I had a spare piece, so it was going to cost some time to repeat the work already spent on the part, probably at least a day.
But that was only the beginning.
I backed off the quill, and tried to remove the workpiece from the of the chuck. It would not budge, so I released the 2mm drill bit (actually a carbide end mill) from the chuck. Well, I tried, but the chuck key would not rotate. The chuck was frozen solid. So I went and had a cup of coffee.
On return, it was apparent that the workpiece was welded to the end of the chuck, and the chuck jaws were welded together at the tips.
So, I released the chuck and its arbor from the mill, and broke off the workpiece from the chuck with a hammer. The weld and the drill bit broke. But the jaws of the chuck were still welded together.
You might recall that I had accidentally destroyed an expensive Japanese chuck some months back, and this one was its “temporary” replacement. Obviously I will need to buy a replacement this time, but I am in the middle of my cannon build, and want to get on with it. What to do?
On close inspection the weld between the jaws stopped about 3mm from the jaw tips. It involved the surfaces between the jaws and the still present carbide drill shank, and the sides of the jaws. So I ground about 3mm off the ends the jaws until they started to move. Then used a tiny grinding wheel in my Dremel to remove most of the weld between the sides of the jaws. At this stage the chuck is looking very ugly, but it works in a fashion, and I was able to resume my drilling. Very carefully.
I did straighten the bent workpiece, but it is RS. I spent the remainder of the day using my spare workpiece, repeating the lost work. No photos of the damage. I was not in the mood.
These are the sides of the second carriage. For this one I am drilling the holes in both pieces simultaneously, by clamping, and then bolting them together. Pretty obviously a better method. Sometimes I am slow learner. But I do try to not make the same mistake more than 3 times in a row.
The “B” carriage on the left, and work to date on the “A” carriage on the right. The bolts will eventually be replaced with rivets.
BTW, I have de-monetised this blog. You should not see any more advertisements. I noted that the income from the ads from the one post on which they appeared, was one cent. Yep. One cent. If I had monetised the site from its beginning, 6 years ago, I would have earned approximately $AUD6 dollars. Nuf said.
Meanwhile, I discovered some more videos from posts 5-6 years ago. I have deleted the videos. A pity about that, but it has created some more storage space and allows me to continue to post on the current plan.
If you have been following the build of the model Armstrong cannon, you might remember that most of the steel panels for the carriage were laser cut a few months ago. In the past few days I have been drilling dozens of 2mm holes, ready for final riveting. Meanwhile the parts are held together with 2mm bolts and nuts. I expect that the rivets will not be installed until I can see that everything fits and works as it should.
Only a few fasteners so far, but it is surprisingly rigid.
The angle iron is cut from the corners of rectangular section tube with 2mm wall thickness. It does require some more finishing and rounding off, but the scale is accurate. The big hole is to allow the hydraulic recoil tube to be inserted. The recoil cylinder will be 18mm diameter.
SWMBO’s comment…. “It looks like it is made from Meccano”. I guess that there are a lot of holes.
Meanwhile I have discovered an excellent reference source, published in 1879. It is a free book, available online at Google Books. “Treatise on the Construction and Manufacture of Ordnance in the British Service”. 517 pages. Original price 9 shillings. It is full of gems for the cannon modeller. As an example, this is a drawing of the sights on the 64 pounder RML converted to 80 pounder. You will see that the barrel shape is different from the one which I am modelling, which is a mark 3. But it is probable that the sights remained the same as those pictured. A great find, with enough detail for me to scale down and model.
Note that the sight on the right is not vertical, but sloped at approximately 2º. That is to compensate for the slight deflection of the projectile to the right, caused by the rifling.
From the same book, a detailed description of the Vent / touch hole / ignition hole. It was NOT just a simple hole drilled into the barrel, but a copper cylinder which was threaded into the barrel. The touch hole was drilled through the copper. The reason for this was that the touch hole gradually became bigger with use, and needed replacement after a certain number of firings. It also allowed repair of the touch hole if the gun was “spiked” by the opposition, but that was a major exercise which required specialist knowledge and tools, and a return to the factory or one of the 5 workshops listed above.
Yesterday I spent some time with 600 grit emery paper on the barrel. A bit more elbow grease is required, but I took some pics of the progress….
From the left, the sighting line called the “line of metal”. There will be a corresponding line on the muzzle. Next is the weight of the barrel in hundredweight. 81cwt = 4 imperial tons plus one cwt plus 2/4ths of a cwt plus zero pounds. One hundredweight = 112 lbs, so this barrel weighs 9128lb / 4140kg. The arrows indicate that the barrel has been “proofed” and accepted for service and also possibly mark the end of bore. The dot would be where the “vent” would be located (the ignition or touch hole) usually about half way along the powder cartridge. Then the reigning monarch’s cypher. In this case, Queen Victoria, with her motto, that of the Order of the Garter. HONI SOIT QUI MAL Y PENSE. The translation from French is “Shame to him who thinks ill of it” (“it” being the Order of the Garter)
The Royal Gun Factory number of this barrel, and axis lines. One reference stated that they mark the centre of gravity of the barrel, but according to my assessment, the COG is well behind this point.
The other trunnion marks are yet to be lasered. Maybe late next week.
I am delighted with the quality of the laser “engraving”. It is sharp, crisp and finely detailed. Again, thanks to Stuart Tankard for the use of his laser, and for operating it.
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.
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.
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.
This is the Queen Victoria emblem and motto on the original cannon at Port Fairy, Victoria.
The “Victoria Regina” emblem, and Order of the Garter slogan motto.
And this is what is now lasered onto the model cannon..
Pretty good, Hey? On the model, the emblem is 20x12mm. It was downloaded from the internet, edited with Corel draw, saved as a BMP file, and then lasered onto the steel model barrel. This is a photo of the emblem on the model cannon. The rectangular background will disappear with polishing.
It was made with a 30 watt fibre laser, driven by its owner, Stuart Tankard. It took about 30 minutes, 200 passes. Shows up my substandard turning.
Shows the emblem appearing after 100+ passes.
and this is an enlarged image of part the laser engraving.
I have some videos of the process, and I will make them available after some editing.
This was incredibly exciting. The model cannon requires more polishing, and colouring with a gun blacking chemical.
We also engraved the cannon weight, sight marks, and year of manufacture on the trunnions. I will post those photos when available.
The small cap screw bolts will be replaced with solid rivets.
The wheel axles are yet to be made and pinned. (the Philips head bolts will replaced with solid pins and washers, and held with taper pins.)
And just to remind you of the appearance I am aiming for…
I do wonder about the original colour of these 1866 cannons. The rusty iron colour has some attraction, but I would be certain that it is not original. So far I have had no luck finding out what the original colours were.