Busy at this time of the year.
Making some wooden toys for the grandchildren for Xmas.
Preparing the surgery building for sale. Removing and storing 34+ years of medical records, moving furniture, arranging repairs and painting etc etc. Feels strange to be no longer a registered medical practitioner, but I know that it was the correct decision to retire. It has taken 2 years to totally burn the bridges by dropping my medical registration, and selling the surgery etc.
Model Engineering Club annual exhibition.
Plus ongoing military history book reading and reviews.
Slashing long grass, to reduce the summer fire risk.
Assembling and installing a kitchen into a rental property.
So it was a treat to get some time in the workshop today. I had previously made the layshaft brackets for the triple expansion steam engine, so I spent a happy few hours setting up an angle jig on the milling machine to drill and tap holes to attach the brackets.
Except for a name plate I have finshed the bombard. The floral design at 12, 4 and 8 is not as clear as I wished, and the Arabic script at 2, 6 and 10 is even worse. But it is cut in wood, and it is a first effort at such work, and it is not easily seen in a model only 106mm 4.2″ diameter, so I am reasonably satisfied.
Also, this was always a prototype, in wood, and I have not totally dismissed the idea of making it in cast iron or brass. In metal I am sure that the detail work would be a lot finer.
Well, I bought a pair of NSK bearings for the Z axis of my CNC mill, and removed the old ones and inserted the new ones. Cost $AUD 200. Plus 2 or 3 half days of dirty heavy work. And the problem persisted!!@!@
OK. Time to get an expert opinion. Here comes the cavalry. Thank goodness for my expert friend Stuart T.
Very puzzling. Even for Stuart. There was some unwanted movement in the Z axis (about 2mm), despite being apparently properly installed. Not a problem with the ballscrew or ballnut. Even Stuart was puzzled.
“have you got any left over bits and pieces? Is it all installed the way it was before?”
To cut the story short, we installed a thicker washer below the locknuts, and it seemed the problem was fixed. Or was it?
Today I did another test run of the bombard mouth Arabic script. Worked fine. OK. Time to finish the bombard.
The translation of the Arabic script is “Help O God the Sultan Mehmet Khan son of Murad. The work of Munir Ali in the month of Rejeb. In the year 868.”
A little unfinished business on my model bombard is the Arabic script and floral decoration around the barrel mouth.
This is what I have managed so far….
It is a practice run in scrap wood.
Some of the detail has disappeared because I used a milling cutter with an end width of 0.5mm. Next time I will add another step using a cutter with a sharp point, and a lot more of the fine detail will appear.
That pattern took a total of 80 minutes to CNC mill, with the feed rate set at 500 mm/min.
Unfortunately my CNC mill developed a problem with the Z axis, probably due to a worn out end bearing. I am hoping that it is not the ball screw nut. Now in the process of removing the bearing. A heavy, awkward, dirty job.
When the mill is working again I will mill the actual bombard model and post some pics.
Computer graphics is not my strong point. To get the CNC mill to cut that pattern I did the following..
I am back onto the triple expansion steam engine, after putting it aside for most of 2016. I am guessing that it is about 75% completed. I have been struggling with this project due to poor plans, no instructions and some lack of skill and knowledge.
When I was well into the project, a colleague pointed out that detailed instructions existed in some articles published in 1985 (Model Engineer, Bertinat). I obtained the articles, and subsequent progress has been greatly assisted, but unfortunately some errors had already crept into my work, and these have not been easily or completely rectified.
So now I am back into it. And I would hope to have it finished and working by the end of the year. Watch for pictures when there is something to show.
I am already thinking about what will follow the triple. Maybe a Harrison 1 clock? (of “Longitude” fame.) Looking for some plans.
Or maybe some more artillery? How about a working model trebuchet? Now that does have some appeal. There are some plans on the Net, but they look over simplistic. I am thinking of a more historically accurate model. The following picture is from an old French encyclopaedia. But I might have to abandon my preferred scale of 1:10 because the original was about 12 meters long. But on the other hand……
It does have some interesting features. The ratcheted windlass, the travelling pulley, the trigger mechanism (“pulling the pin”), and the projectile release mechanism (trying to avoid the projectile going up vertically).
There is the 1464 Turkish bombard (black), 17 tons, 307kg granite ball; the 1779 long naval gun off USS Constitution or HMS Victory 24lb balls; and a 32lb carronade. All 1:10 scale. Interesting to see them together on my kitchen table?
I would have preferred that the title of this blog was “Finishing the Ottoman Bombard”, but I am still waiting for the vectors of the barrel mouth decorations and Arabic (?) writing, and the touch hole.
But I have at least painted the bombard, and the pictures follow. You will notice that I have not attempted to reproduce the bronze or copper colours of the orginal in Fort Nelson. Partly because I doubted my ability to make painting such variegated patterns realistic, and partly because the cannon would not have looked like that in its heyday of 1464. It would probably have been either black, like most SBML cannons (smooth bore muzzle loading), or possibly gaudy golds and reds and blues like other medieval items. So I painted it black. I like it. If I get evidence that it should be more colourful I can change it later.
This is the low res photo from Fort Nelson. High res photo on its way.
In the meantime, I have contracted with a US firm to convert the picture to vectors. More $US. ($US50 to be exact).
I am not sure that this is going to work. But I will report to you.
I do wonder what that the Arabic/Turkish writing means. Does anyone know? I am pretty sure that it is not complimentary to Christians/Westerners/Non Muslims. Maybe it is just an instruction not to look before the touch hole is touched. Or “do not stand here”.
PS. Note added 17 Oct 2016. The translation is “Help O God the Sultan Mehmet Khan son of Murad. The work of Munir Ali in the month of Rejeb. In the year 868.”
868 = 1464 ce.
Does anyone have a decent photograph of the writing on the muzzle?
I have repeatedly hunted through every picture which I can find on the net, but they are either taken at an angle, or too poor quality to be useable.
Does anyone have a photograph which I could beg buy or borrow?
I also need a photo of the touch hole.
I have contacted the Fort Nelson Armoury Museum, but not too surprisingly there was no response.
Is there someone in the Portsmouth UK area who could pop in and take some pics for me?
POSTSCRIPT: October 5. I have had 2 excellent and positive responses to my appeal.
First, reader Richard sent me a connection to a Turkish Dr/Professor, who has made a 1:25 model of the bombard using 3D printing. (at least that is how I think he has done it. My Turkish is non existent). I am following this lead.
Secondly I have had a response from Fort Nelson Armoury, with a good photo of the barrel mouth, and a high res photo on the way, after payment of a significant, but not unreasonable fee. Isn’t the Internet wonderful!!
I have found this video to be particularly useful in my modelling of the Ottoman bombard. The subject of this video is the gun that the Turkish sultan gifted to Queen Victoria when the Brits and the Turks were allies. It might be one of the guns which fired on the British fleet in 1807, when it (the gun) was 343 years old!
Notice the colour. It is aged bronze. I am thinking about how to reproduce that colour on my model.
Length of the assembled gun 5.2m (17′)
Breech weight 8942kg
Barrel weight 8128kg
Average weight of shot 307kg
the model is at a scale of 1:10. photos soon. being painted.
There are 16 pins at each end of each section of the cannon.
These were certainly used as leverage points, for very strong men with large levers to rotate the 8-9 tonne segments against each other to engage and tighten the screw.
I cannot see how the pins would have been cast with the breech and barrel. For my model I decided to make separate pins and fit them into the gap between the big rings, then insert a grub screw through both rings and the pin. The holes are then filled.
I wonder if a similar method was used in 1464. I would love to have a close look at the original cannon to figure this out. From the photographs, I can see no evidence of later insertion of pins, but neither can I see how it would have been done any other way.
The holes are now filled with wood filler, and will be sanded flush. They should be invisible after painting.
Next the painting, the stands, and some cannon balls. How to reproduce that aged copper colour…
The decoration around the barrel is formed by a repeating pattern, which when milled, very cleverly forms 2 identical patterns. One is excavated and one is the original barrel surface. You will see what I mean if you look at the pictures in the earlier blog, and the video below.
It took me an evening of experimenting on the computer to work out the system and draw it.
Then I measured the diameters of the 2 gun components, calculated the circumference, (OK it is not rocket science. 3.142 times diameter), then working out the number of identical shapes which would fit around the 2 different diameters, at the same size and spacing. Amazingly, it took 18 shapes to fit almost exactly around the barrel, and 16 of identical size almost exactly around the breech. the angular spacing was 20 degrees and 22.5 degrees.
Then the shape was imported into V-Carve Pro, and G codes were generated.
My CNC mill does not have a 4th axis, so I used a dividing head to move the workpiece at the precise angles. See the setup in the video. That meant that the pattern was engraved into 16 and 18 flat surfaces, rather than a continuous cylinder as on the original.
It worked very well. There were minor compromises due to the shapes being milled with a fine end mill but when you look at the pics I hope that you will agree that it is effective.
I calculated that the milling had to be at a maximum depth of 2mm in order to cope with the curvature, but if I do it again, I would reduce the depth by 25%.
The first part of the video is a shot of CNC drilling. Then the CNC routing of the repeating patterns. Each angular setting of the pattern took 4 minutes to complete. 136 minutes altogether. In reality, it took a whole day, most of which was spent doing the setups.
Another session or two, and this project is complete.
Now how do I make a cannon ball 62-63 mm diameter? In wood will be ok? Does not have to be granite. I could make a mould and cast it in aluminium or lead, but stone would be authentic….. thinking.
ps. Re cannon balls. I will cast them, in cement! Now, how to make a mould.
The breech and the barrel are joined with a very large thread. On my 1:10 scale model it is 60mm diameter, and has a pitch of 6 mm. These dimensions are measured off Internet photos of the original bombard, so they might not be faithfully accurate to the original bombard. If anyone has accurate plans of the bombard I would be very interested to hear from them.
I experimented with various spindle speeds, feed rates, depth of cut, and finally decided that red gum wood is not the ideal material to be cutting a thread with sharp points. However, at 200rpm, and taking 50 cuts to reach the full depth, and using a very sharp tool, the end result was OK. I will fill the tearouts.
In order to make a functional join in the wooden cannon, I truncated the apex of the thread. In the gunmetal version I will attempt a more faithful to the original, sharp look.
For some reason, the wood held together better during the internal thread cutting than the external.
The male thread was cut on my newly CNC converted lathe, between centres, but the fixed steady on that lathe was just too small to hold the barrel, so the internal thread was cut on my bigger Chinese lathe.
Next I will bore the barrel to 63mm, then turn the exterior of the barrel.
So if you watched the video, you can see that I have a problem with the big thread between the breech and the barrel, at least in the wooden prototype. It might work better in brass or gunmetal.
The thread has a pitch of 6mm and a diameter of 60mm. It is big.
My plan at this time, is to make a brass male threaded section, and glue or screw it into the breech. Then to make a steel tap using the same G code, and cut a thread into the wood of the barrel. (p.s. note 30 Sep… I continued to experiment with feeds, speeds, and cutter shapes in the wood. The final result was OK so I did not make metal threads. That will have to wait until I do this project entirely in gunmetal or brass… maybe never)