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.
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.
I spent few hours finishing the racks today. But not yet installed. Some photos.
For once, a job proceeded without a mistake. Hooray. Hmmm. Look at that big gear. Thinks… “I quite like that blackened inner area with the polished bronze hub and teeth”.
(p.s. For non-Australian readers, “rack off” is an expression sometimes used in Oz, when telling someone to leave or desist, in a forcible, but not quite foul manner. Used in the post heading in a hopefully, mildly humorous effort to be eye catching.)
The final gear in the cannon carriage positioning train is a rack gear. It is 198mm long, 7.2mm wide plus tabs for bolting it to the carriage of the model Armstrong cannon.
A rack gear is a flat gear, and it is cut with the same cutter (number 8) which makes a circular gear of 135 teeth or more.
The teeth of a circular gear are cut by dividing 360 degrees by the number of teeth. But the pitch of the teeth of a rack gear is determined by a formula found in Machinery’s Handbook. rack gear pitch = module x 3.1416. Which for my module 1.25 = 3.927mm. Hmmmm. 3.1416. That is a familiar number. Light bulb in brain switches on! A rack is just part of a circular gear of very large diameter.
At first I thought that I would use the same mill arbor which I had been using for the circular gears, but as soon as I started to set it up I realised that the stick out of the arbor would be ridiculously excessive. So, reluctantly, I set up the horizontal milling attachment of the mill. Reluctant, because the attachment is heavy, fiddly, and time consuming. Luckily, I had a 22mm shaft for the attachment, the correct diameter for the cutter. I had never used this shaft before, and it was missing the nut, and bronze bush. Bought it on Ebay years ago. Found a suitable nut and made a bush.
This is the setup. The 350mm shaft was not long enough to make the rack in one setup, and it took a bit of trial and error to work out the best compromise.
I need 2 racks, so I will split this one down the middle.
Did not have a piece of bar stock big enough for this job.
A bit of a story about that heavy horizontal mill attachment. When I bought it some years ago, I put it in the rear compartment of my SUV. But on the way home my SUV was T-boned by an idiot at an intersection. No injuries, but a big expensive dent to the passenger side of my SUV. Air bags activated. And the rear window was smashed. I could not figure out why the rear window was broken. After the police and fire engines had finished, and the tow trucks arrived (my car was out of action for 2 months, the other vehicle was a write off), a by-stander approached me with a familiar object which he had found in the gutter on the OTHER side of the 8 lane highway. Yep! It was the horizontal mill attachment. Been flung through the rear window by the violent impact of the collision, and across 8 lanes of the road. It was scratched, but otherwise intact. And thank goodness, it had not hit me or anyone else in its trajectory!
The big bronze gears on the bottom row were cast, had M1 teeth cut, had the teeth machined off, a bronze ring silver soldered on, and M1.25 teeth cut, which is what you see. They are almost finished. Above them are an almost finished M1.25 pinion and a pinion which will be parted from the stock bronze shaft tomorrow.
The right hand smaller gears are M1, with teeth cut. The right hand one started life like the ones on the left, but was a reject. I machined off the outer ring, and part of the spokes. and silver soldered on a new outer ring, and machined the M1 teeth. The similar solid gear has been made from bar stock from scratch. The spokes will be CNC machined, maybe tomorrow.
The bar at top has M1 teeth machined, ready to be bored for the shaft, and gears parted off.
The pinions for the big gears have a 4 tooth ratchet. This will allow the gear train for carriage movements to be disconnected for firing.
Making the big spur gear which pushes the gun carriage up and down the inclined chassis has been a bit of a saga.
For a start, I decided that fabricating it with lathe and mill was going to be very difficult, and it was an obvious candidate for casting. In bronze. After making a model with 3D printing in PLA.
So, I drew up a 3D model, saved it as an STL file, and printed it. But did not take into account shrinkage of the PLA part. Or shrinkage of the cast bronze part. So instead of 58mm diameter, the blank gear was only 57.4mm diameter. By reducing the number of module 1 teeth to 57, I could get a reasonable gear, and the teeth were duly cut.
But, module 1 teeth looked skinny and pointy and not correct. Plus, 3 of the cast gears were total casting failures and were discarded (remelted).
So, I machined off the module 1 teeth, made some bronze disks, and silver soldered them onto the cast central hubs and spokes, and machined the blanks to 60mm diameter. By this stage I had decided that the big gear teeth should be module 1.25. Chunkier. Looked the part.
But I did not have 1.25 module gear cutters. And no-one in our club had them for loan. So I ordered a set from China. Delivery any time up to the end of November!! Then I found 2 of the set from an Australian dealer, but they were priced almost as much as the full set of 8 cutters from China. But, thinking that they would arrive more quickly I bought them. They were Chinese. It is a seller’s market.
Then today, at our GSMEE meeting Swen P said that he had a set! And I could borrow them! So, gratefully, I did. And I cut the teeth this afternoon.
While the teeth were being cut, I tidied up another bronze T rex.
Next to cut the M1.25 rack. Should be straightforward.
Just to recap, I made the trees and investment powder moulds about 2 weeks ago.
The first problem was that when I was adding the carefully weighed and expensive investment powder to the carefully weighed water, the f***cking scales timed out and shut down. So I had to guess the amount of powder to add. Then mix furiously. Then a briefer than normal degassing. All to be completed in 10 minutes. 10 minutes sounds like a long time. But it is all too short when there is any hick-up at all. (read.. “stuff -up”). #1.
I knew that the scales had a shut down timeout, and following the Chinglish instructions, I thought that I had turned the timeout off. But apparently I had not. After that I ordered some new scales.
Then I had to wait almost 2 weeks for the 15% phosphor copper to arrive.
Yesterday, after installing a new heater element in the melting furnace the day before, I fired up the investment oven and went through the drying, burnout and baking cycles, about 8 hours. And prepared another tree and mould for the next pour, in a few days time.
The melting furnace with its new element took a lot longer than previously to melt the bronze ingots, about double the time. But that was OK. Just had to ring SWMBO to warn her that I would be very late. (Got home about 9pm. She had organised take away.)
I added the 15% phosphor copper in approximately the recommended amount. And poured the first cylinder. But I forgot to wait the recommended 2″. #2.
Then I poured the second mould. And there was not enough melt!!!! #3. I had underestimated the amount of bronze! Those 4 big gears were guzzling the molten bronze! So what to do? Abandon the second cylinder? Or melt another ingot and just pour it on top of the first one after another 30-45″?. Nothing to lose, so I plopped in another bronze ingot, and waited for it to melt. Meanwhile I put the mould half filled with bronze back in the investment oven to keep it warm at 710ºc. Then, for some reason, the electronic controller of the investment oven shut down, and the element stopped heating. #4.
When the extra bronze melted I added bit more phosphor copper and completed the pour into the now substantially cooler mould which was already half filled with bronze which presumably had solidified. I assumed that the join between the 2 pours would be a problem. And it was.
Forgot my camera. Some photos to be inserted here later.
Somewhat surprisingly considering the guessed amount of investment powder at the original mix, and short duration degassing, the first mould was, apart from a few bubbles, completely successful. The second mould, with its 2 pours, was not a total disaster.
Today I sawed apart the trees, removed the bits of sprue and vents, and partly machined the parts. These are the bits.
The toothed gears and non toothed gears are the biggest gears on the cannon. And they include the drum brake, I was unsure whether the cast teeth would be adequate, or whether I would need to cut the teeth. It was not a fair test, in view of the interrupted pour, and the brief degassing. But I will cut the teeth from the blank wheels to the right. The toothed gears were probably the join between the 2 pours and total failure and will be remelted.
Even the blank wheels are not without problems. I did not allow for shrinkage, #5. and the diameter of the wheels is 57.5mm instead of the intended 58mm. So I cannot cut 56 teeth per wheel. I can cut 55 teeth on the smaller diameter. Still pondering that one. Do I repeat the entire exercise with a machining allowance? Or just be satisfied with one tooth less? I have not decided definitely, but am tending towards accepting a slightly smaller tooth count.
But, at least the brackets to the right came out well. This photo was taken after some belt sanding….not perfect, but not bad at all.
Incidentally, the T Rex is quite good. substantially less surface oxidation, and the oxidation layer that was present came off much more easily. Next pour I will add a bit more of the phosphor copper. And I will wait the recommended 2″.
The model Armstrong cannon has 7 gears, 2 of which are bevel gears, and 5 spur gears, including one quadrant gear.
The spur gears will be machined and cut from bronze, brass or steel. I have a set of module 1 cutters, which are close in 1:10 scale to the originals which are close to module 10.
The bevel gears I have made by casting them in bronze, teeth and all, and they are pretty darned good. Not perfect, but they will be hidden from sight in the gear case. They seem to mesh pretty well, but, if they are not up to the job of elevating the barrel I will cut some replacements.
The biggest gear is a spur gear, and it has a brake drum as part of the casting. It is a bit more complicated than a simple cut spur gear. Apart from the brake drum, the gear teeth have flanges at each end of the teeth, which will make them difficult to cut, unless I add the flanges later. I guess that the original was cast, teeth and all.
After 4 -6 weeks of making castings, and remaking them, and remaking them again, I have finally started drilling holes and bolting pieces together, in preparation for final riveting.
I ground a 2mm diameter end on my centre punch so I could transfer the cast holes on the brackets to the sides of the carriage for drilling. (using a toolpost grinder on my lathe to grind the center punch.)
I could not resist pushing some parts together to visualise how the carriage will appear. 10 wheels per carriage to be made. This is the “B” carriage, on which I try out the techniques.
Using my new riveting gun, I inserted a lot more rivets on the “A” chassis…and I used a technique suggested by one of my readers…bearing in mind that my first riveting efforts marred the surface of the parent metal, and were generally rather irregular rather than neat.
Virtually NO surface dents, very regular, a big improvement. I had intended to polish out the machining swirls, but SWMBO said that they were appealing and interesting.
And the technique was this….
The rivets are inserted 5-10 at a time, then the heads are covered with tape. Duct tape in this case. The work is then turned over, and the rivets do not fall out.
Each rivet head is centered over the anvil, and the pneumatic gun is used with the snap on the other end. The tape stops the rivets from falling out, and also protects the parent metal from the snaps. I experienced virtually no parent metal bruising. And was VERY fast. A major improvement. Many thanks Timothy G!
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.
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.
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.
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.
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.
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.