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.
Some parts on my model Armstrong cannon could not be made until measurements were checked on the assembled model.
The projectile loader was one such group of parts.
The 80lb projectile obviously sits on the cradle. The carriage is at the top end of the chassis, with the barrel angled down by 17º. The arm with the cradle swings around and meets up fairly precisely with the muzzle of the barrel. I am not sure if the projectile is placed on the cradle before or after it swings around. (does anyone know?)
I had these photos, and a few measurements of the loader assembly from the Port Fairy cannons, so I drew them up in 3D.
The components of the loader are fairly simple, and can be machined rather than cast. But I printed the components in PLA so I could test the design before I started to cut metal.
But, when I positioned the PLA assembly on the cannon, it was clearly incorrect. It did not line up with the muzzle of the barrel.
I have not yet decided whether to machine the parts or cast them in bronze. Both processes are a lot of fun. I will reprint the curved arm in either case.
Well, actually, it is a 1:10 scale model of a 5 ton cannon. The model weighs around 5-10kg at a guess.
The brake is to control the descent of the barrel/ carriage down the 4º slope of the 5 meter long chassis.
On the original, the brake was a steel band on a steel drum which was attached to the big gear.
This is how it appears on the scale model..
I was a bit apprehensive about this job. The lever is very close to 2 gears. the steel belt has to be properly tensioned, because the degree of movement of the control lever is quite restricted. And the width of the band has to be slightly less than the 5mm groove on the drum.
But, I found these…..
So, for once, my apprehension was not warranted. The job was fiddly, but no major mistakes!
WTF! I thought that this site was about model engineering, metal working etc.
Well. I just need to say that typists correction fluid is an essential tool in my workshop.
Not for typing, I hasten to add. But for silver soldering….
Today I needed to silver solder an extra 1mm thick disk to a tiny part, which already had 2 silver soldered joins. I had spent an entire workshop session designing and making the part, and I did not want it to fall apart when I added an extra component. Which I admit, was an afterthought.
And the central hole in the extra disk HAD to line up precisely with the threaded hole in the previously made part.
I had been advised by another GSMEE member that a metal surface painted with typists correction fluid WILL NOT accept silver solder. I have tried this method once before and it works. This is another demonstration.
This handle locks the elevation gears into position after the cannon barrel elevation has been set. Several more hours were required to file a central tapered ridge into the added material, and a corresponding groove where it rests. It all worked out OK.
Typists Correction Fluid. I hope that it never disappears from OfficeWorks.
Thanks again Frank Marrian GSMEE, and jimmymouse, for this great tip.
Attached the recoil tube yesterday. But I cheated. It is a gas strut.
But, it is SO close to the dimensions that I required, that I decided.. what the hell. It is 18mm diameter (17.5mm required), and 200mm long (198mm required).
I degassed the strut by drilling a 1mm hole, and the gas came out under considerable pressure. I had to do that, because the strut was too strong for the cannon. Even degassed, the strut has enough shock absorbing action to be useful and realistic. I made some brass brackets and a cap, for visual consistency.
Today I made the lever which locks the elevation gears.
Yep. To make my models I use a computer for drawing, making lists, ordering fasteners and materials and tools on Ebay and from suppliers, driving CNC 3D printer, driving CNC machining tools. And laser marking parts. I also do a lot of traditional machining, hand filing and sanding.
The cannon barrel will elevate to 30º, and depress to 5º for firing, although in practice deviations from a degree or two from 0º were rare. Plus there is an extra mark for 17º depression, which was the reloading angle. The numbers which the laser marked are only 0.6mm high. Hard to see with the naked eye. But in scale.
Lasering the tiny marks and numbers took 2 seconds per pass. That is, 2 seconds to make all of the marks and all of the numbers. After some experimenting, we settled on 50 passes. Which was still less than 2 minutes per part.
Click on the following frame to see the video…
How fantastic is that????
So quick, precise and clear. Yep. I am quite happy to employ any new technology which is available to me.
Then today I made the fittings to secure the recoil tube, and drilled and tapped the 8BA fasteners.
The recoil tube is a commercially available gas strut. It was so close to my 1:10 scale dimensions that I decided to cheat, and use it.
I drilled a 1mm hole in the gas tube to release the gas and oil, turned and re-threaded the front end of the piston rod to 6mm, and made the brass supports and end cap. I released the gas because it was too stiff for the model. Even without the compressed gas the strut has some “shock absorbing” activity, and I am quite happy with the decision.
I suspect that this post will not be of much interest.
But the parts represent 2 whole days in the workshop, so I am writing these notes for my own diarising more than your entertainment.
The chassis of the model Armstrong RML cannon has a cross bar, which is bolted to the longitudinal bar, and is attached to the side girders with some small, shaped clamps.
The cross bar doesn’t look much, but it has 4 bends and a twist. The space was too tight for me to measure the angles, so I bent the cold bar by estimating the degrees by eye. Same with the twist, except that the twist had to be confined to the section not attached to the girder or the central longitudinal bar. So I heated that to red heat with oxypropane. The twist was 4º. But I eye balled that too.
The clamps required some planning. I considered machining them from solid bar, but work-holding was going to be problematic.
So I silver soldered 2 strips together, cut off the pieces, then sanded, filed, and manually bent the angles.
p.s. Another day later, more of the same…
I would prefer to use 2mm metric bolts rather than 8BA, which is a similar diameter and pitch, but unfortunately I have been unable to find a supplier of 2mm bolts with hex heads. BA bolts are several times more expensive per piece than metric, and it adds up when using hundreds per cannon.
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 .
2 days in the workshop, and not much to show…. just one photo.
The curved brass bar is a protractor for measuring degrees of elevation of the barrel. I used High School trigonometry to work out the distance from the pivot point at the centre of the trunnion, to the pivot centre at the fitting under the barrel.
Then cut out the shape from 2mm brass with the CNC mill. That was the easy bit. Although it did takes 3 goes to get the radius of the curve correct.
Today, although feeling depressed after the Cats loss last night, I made the cross bar with the rectangular cutout, then spent a couple of hours bolting it into place. It all works smoothly. The rectangular cutout is 2.2mm wide and 7mm long. I chain drilled with a 2mm carbide milling bit, then milled the slot sides, then filed the corners square. It is stainless steel. Slow work.
I have not worked out how to engrave the protractor marks, which are at 0.25º intervals for elevation, and whole degrees for depression. I could ask Stuart T to engrave it for me. The design and actual lasering would be straight forward, and I am sure that Stuart would help if requested. The problem would be to align the part on the laser machine, so that the engraving occurred exactly at the correct location. Actually, as I type this, I think that I have the solution. Watch this space.
I need to make a pointer next, and to determine the 0º position. The carriage sits on the chassis which is at a 4º slope. Not rocket science, or brain surgery. Just need to get it right!
I made a 1:10 model of this Ottoman bombard a few years ago. This one was made in 1465, and is thought to be a copy of the bombards which brought down the walls of Constantinople in 1453. This one resides in the Royal Armories Museum at Portsmouth, UK, and I photographed and measured it in 2019. It has a bore of over 600mm, and fired stone balls of over 350kg.
Last used in anger against the Brits in 1807, where it and others like it, were instrumental in preventing a British fleet from invading Istanbul (renamed from Constantinople). How many weapons have an active life of ~350 years?
So I am contemplating making a model at the same 1:10 scale, like the original, in BRONZE. It will have the same shape and size, but will look like and feel like BRONZE.
I still have my original measurements and drawings of the model. So my plan is to print the cannon parts in PLA, taking into account my extra information from the 2019 visit, then to cast it in BRONZE.
I had planned to stop this blog after finishing the Armstrong RML, but maybe , if there is enough interest, I will keep it going for the next project. You will need to let me know if this project will be of interest. Because lately, comments and likes are few, and numbers have been discouraging. And the renewal date for WordPress is approaching. I get it that people prefer videos, but that is not my style. If this written plus photographs style is not wanted then I will not persist.
The part measures 20x12x7mm. And it has some tiny details.
The design is simply and quickly drawn on V-Carve. A rectangle with rounded corners for the base, and a rectangle with 2 arcs on each corner of the column. Circles added for fastener holes.
This is where it ended up….
There are many ways to approach the machining of the part, and this is the technique which I used……
The control wheel for the elevating gears was found in my rejects box. It was made for the triple expansion engine. It looks pretty good? Cant remember why I rejected it for the triple. Maybe my standards are lower these days.
There are not many photos of these cannons on the net, and none of them show this wheel. Or was it a simple handle? The shaft has a squared end for a wheel/handle of some sort. So this wheel is my best guess as to what would have or could have been used. Virtually all of the cannons remaining of this type have had the small parts removed/souvenired/stolen which is sad. Some old photographs of bigger Armstrong RML’s show wheels of this type, so I feel justified in making this design assumption.
Another design consideration. SWMBO likes the cannon without the chassis, as in the above photo.
But this is how it looks on the chassis.
The gun and its carriage have brackets which make separation from the chassis very difficult/almost impossible. So I am considering a design modification which would permit a choice of with or without chassis. What do you think?
(please note. this is a MODEL cannon, has no touch-hole/vent and is therefore not capable of being fired.)
Firstly the right hand carriage side was removed from the carriage.
I turned a disk with a small hole to locate one arm of the dividers at the centre of the trunnion, and positioned the quadrant gear. Then super glued it, and its pinion, into position. Marked the locations. The super glue will be removed later.
The bevel gear case was located through the pinion gear hole, and keeping the control handle shaft level. The case was drilled and bolted into position. The control handle shaft will be replaced by one of smaller diameter, in keeping with the 1:10 scale.
A couple of days in the workshop working out how to position those parts and drilling, tapping, and reaming. The other cannon will take less time.
I had 3D printed another tree with 4 cannon parts. Brackets. The complete tree fitted into a steel flask 100mm diameter and 120mm high. So I repeated the steps of the last successful pour, and painted the tree with investment slurry, mixed the main investment, degassed it, poured it, and degassed the entire flask, investment and all. That method had worked well before, so I repeated it.
But I was a bit concerned because the investment was only a few mm thick at the bottom of the flask. Would it hold up? Read on.
So then commenced the drying, burnout, and baking cycles in the potters oven. Normally it is about an 8 hour process, and I did not get to start until 12 midday. So I was in for a long day.
But then the oven started to play up. It would suddenly switch off. The temperature gauge would swing wildly. And would not heat above 400ºc and it needed to reach 710ºc.
I did not know the source of the problem. Thermostat? Wiring? Controller? Power supply? I did know that the thermostat wire was not rated for temperatures above 600ºc, but it had worked OK previously. So I turned everything off, and removed the electronics compartment. Changed the thermostat wire to the proper grade (thanks Stuart!), then found a loose main heater element join, so fixed that too. It all took another 1-2 hours.
Started up the oven again. The temperature had dropped to about 200ºc, but the the temperature started rising slowly, so maybe the problem had been fixed? By this time it was 4pm, and there were still 7 hours of heating required, so it WAS going to be a late night in the workshop. Made my peace with SWMBO. She was happily watching the footy, and not too worried about about my travails. (and our team won convincingly!)
To finish this story, I eventually poured the bronze, and my earlier concerns about the thin layer of investment at the bottom of the flask were realised. The bottom fell out, and molten bronze poured out through the breach. I normally rest the flask in a tray of sand when pouring, and fortunately, the bronze seemed to harden when it hit the sand, and the outflow ceased.
This was the result….
I have several machines which use 40ER collets. I have enough collet spanners, but only one locking spanner for the chucks, and it is always on the wrong machine. So I decided to get some more locking spanners, and I sent my drawing to the laser cutting company. I picked up 4 spanners from them a few days later. Cost $AUD55. (cheap!)
Not much happening to show visual impressions, so fewer posts, but lots of hours making bits function.
The adjustable parallels do not get a lot of use, but they are very handy to align parts in horizontal positions, like the holes in the end caps above. Especially when the girder is at an odd (4º) angle, and even the bottom of the girder is at 1º.
Currently I am planning the making and installation of the barrel elevation gears. Here is a PLA version, paper clipped into position.
Very handy having plastic versions to decide drilling positions etc. In the above photo is a plastic version of the main elevation gears, printed at the correct centres. The little bronze bit is the casting which is screwed to the barrel.
And just to demonstrate the current appearance of the cannons….. Lots of bits yet to be added, but it is exciting to see the size and form of the models.
Do you know what tension drilling is? Well, read on.
Having made the gears which position the carriage on the chassis of the Armstrong RML model cannon (I assume that regular readers will know by now that RML stands for “rifled muzzle loader”), I had to drill the chassis for the gear shafts.
There are 3 shafts, 8mm, 6mm and 5mm diameter. I knew the theoretical distances between the shaft centres by applying formulae taking into account module and tooth numbers. And also by using “Gearotic” software.
But! I did not know the distance between the big gear and the rack gear. Because, the rack is attached to the base of the carriage, and the big gear is attached to the chassis. Considerations such as trolley wheel diameters, rectangularity of chassis and carriage, and position of the trolley wheels on the carriage all come into play. I will not bore you with details, but determining that measurement involved a lengthy, tricky, and complex setup using a surface plate, height gauge, adjustable parallels, straight edges, and averaging the errors. Amazingly, it turned out OK.
Then came a decision. To drill and ream straight through both girders at once, or to measure and drill/ream them individually. Luckily for me, I had a visit from GSMEE member Swen, (to borrow a tool), who is a retired ex-army Warrant Officer artillery fitter/turner. When I explained my dilemma, he was in no doubt. Measure them and drill them independently, he advised. So I did just that.
But, having invested many, many hours to date in making the chassis’, drilling a big (relatively) hole in the chassis girder was a very tense moment. (hence “tension drilling”).
Before drilling any more of the 6 holes required, I tested the fit between the rack and the big gear. Amazingly, it seemed pretty good. Maybe a little bit tight, but not too bad. So, I drilled and reamed the remaining holes.
That photo represented a very long day in the workshop. I think that I arrived home about 9pm.
And there was a problem.
The big gear and its partner would rotate freely in one direction, but were catching and lumpy in the other direction.
Closer examination revealed that the teeth of the pinion appeared to be bent, allowing free movement in one direction only. Hmm…. how could that have happened? And how to fix it?
Root cause analysis of the issue concluded that the mill Z axis must have been bumped when I cut the teeth on that gear, causing them to be slightly off centre, producing the “bent” appearance. (the top photo shows the faulty gear. Can you make out the distortion?)
Solutions? Make a new gear. Or fix the distorted one. I decided to try the second option. I was not wanting to make another ratchet. So, I filed and tried, filed and tried, filed and tried…. you get the picture. And gradually the lumpiness disappeared. Several hours later, with blisters appearing, it seemed quite good, and will not be visible to casual inspection. You, dear readers, will be the only ones to ever know.
Yesterday I drilled the second chassis. I completed the task in only 2-3 hours. A fraction of time compared with the first one.
One of my readers made comment about the pliers which I used to hold the domes of 2mm copper rivets while I threaded them.
The pliers are worthy of comment, so I decided to say a bit more about them, and also some other pliers which are often used when I am working with tiny fasteners.
These are the pliers which started this line.
Finally, the most expensive tiny pliers which I own……and probably the best…
All of the above tools, and many others in my workshop, were purchased over many years at Qualitool Tools, 77a Mercer St, Geelong 3220. tel 035221 8915. David, the proprietor/owner is incredibly knowledgable and enthusiastic about tools, and was a supplier to the aircraft industry, and also to auto mechanics. He stocks only good quality tools. I often pop in there to ask “what is new?”, and invariably he will demonstrate some fabulously useful (read “expensive”) tool which I cannot continue to live without buying. If you are in Geelong, you should visit for a wander around Qualitools. David has no idea that I have given him this rap. Nor do I have any pecuniary interest in his business, except that I hope that it continues. I am happy to support it.
Another small bronze pour yesterday, and it was my best one yet. No bubbles. No voids. And excellent surface definition. What did I do that was different?
First, the 3D parts were printed already attached to the tree. So the trunk and branches were 3D printed with the parts attached. That meant that I could determine more accurately the bronze flow, the gaps, the spaces. The only “failure” was that I added some wax air vent sprues as an afterthought. And those wax parts were the only part of the pour which failed. Fortunately, the absence of the gas vents did not seem to matter.
Next, I painted the tree with a slurry of investment. The slurry was much more watery than the normal investment, but it was thick enough to leave a thin layer of investment on the surfaces, paying particular attention to the corners and internal edges.
Then I used my new, 1 hp vacuum pump to degas the investment mixture. It took about 15 seconds to reach maximum negative pressure, compared with about 1-2 minutes which the 1/4 hp unit was taking.
Then, after pouring the investment, I placed the full flask containing the tree and investment, and degassed the entire unit. I was shocked at how much extra air bubbled out.
The rest of the process was as usual, drying for 4 hours (except that this time it started at 6am, having put the process on an automatic start timer), burnout 2 hours, and baking 3-4 hours.
While the investment flask was cooking, I experimented with the bevel gears which move the cannon barrel elevation. I had cast some bronze gears, teeth and all, some weeks (or was it months?) ago, but was not happy with the result. So, I had bought some bevel gears on Ebay. They are spare parts for an RC model car. Not quite the correct size, but close. The metal is HARD. Sintered? But, machinable with carbide cutters. (ps. added weeks later. Even carbide cutters struggled with machining these gears, so for the second set I used a tool post grinder on the lathe. That worked well, and produced a better finish.)
Now before you all start shouting at me to make the bevel gears from scratch, let me just say that I might do just that. Not yet decided.
This was a feature of the model Armstrong RML cannon that I was not looking forward to. (to which I was not looking forward. Plogies to W Churchill. Something about split infinitives).
It is small, cannot be CNC’d with my degree of knowledge, and requires a lot of stuffing around. Which means filing. Or in my case, use of a Dremel.
This is the result after 5-6 attempts. It will have to do.
Occasionally I have a good idea, try it out, and after it works, I think “I should have taken some photos of that for the blog”.
Today I had one of those moments.
This was the result….
This morning, at the GSMEE Zoom meeting, I asked my fellow members where I could obtain some rivets which I could NUT into position. The reason being that some rivets in my cannon chassis are located in impossibly small cavities. And the dome end of the rivets are visible. Apparently “rivet-bolts” are available, but I could not find a supplier by searching my usual suppliers. One GSMEE member had some spares in BA8, but I suspected that I would need more than his small supply. And I was concerned that the dome head size might not match my copper rivets already installed.
Then I had a brainwave! Why not put a thread on my existing copper rivets! So that is what I tried. And it worked!
The biggest issue is not damaging the copper rivet head while holding it and running a threading die down the shaft. The copper is very soft.
The rivets in the photo above have a shaft diameter of 2mm. And the head is easily damaged.
So I tried this…..
And a 2mm threading tool was required…
Holding the rivet like this does leave a 4mm non threaded length of rivet shaft, but it can be packed with washers, or something else. It works!
So that was my brilliant idea for today. HEY IT WORKS!