It took a whole day making and fitting the top caps of the trunnion mounts from brass.
It took a whole day making and fitting the top caps of the trunnion mounts from brass.
Obviously it depends how many machining operations are required per part, but these days I find that one or two parts per day is about all that I can manage. That includes deciding on then finding the material, drawing up the part in CAD, mounting the material and the cutter(s), then machining and finishing time.
Take today for example. My aim was make a steam pressure valve for the Trevithick Dredger Engine. It consists of a lead ball weight 30mm diameter, a lever arm with a hook, a simple stand with a M6 male thread, a movement restrainer, and the seat and valve. 6 fairly simple parts. I thought that I might get it all done in one day.
But at the end of the day, all that I had made was the arm, stand and restrainer. 3 simple parts.
Admittedly the arm is stainless steel of unknown grade. I broke 2 (4mm) cutters before I had slowed the milling feed rate to a snail’s pace 40mm/minute. Machining time for that part was over an hour! Then at least another hour of hand filing and finishing.
It is just as well that the worst day in the workshop is better than the best day of working!
And next will the interesting job of making the 30mm diameter lead ball weight. Still thinking about that one.
The copper tube which I am using for boiler shell has 6 holes, intended for another project by the previous owner. Here I am trimming the length, so 2 of the holes will eventually be removed. Using a drop bandsaw, with a wooden plug so the tube is not bent by vise pressure.
And today I made some parts for the boiler’s removable flat end. My CNC mill is out of action, so GSMEE President Brendan kindly allowed me to use his machine.
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..
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.
It has been a while since I posted, but I have been busy.
Some of that has been in the workshop making a scale model carronade.
A carronade, in case you are wondering, was a muzzle loading cannon, made 1776-1852 in the Scottish town of Carron, by the Carron company. And subsequently much copied elsewhere.
It is a cannon which is short, squat and ugly.
Weighs about 1/3 as much as an equivalent bore long gun, (see previous posts), requires only 3 men to operate (compared to 9-11 for a long gun), and can fire balls or other nasties at 3 times the rate as long guns.
2 carronades, 68 pounders, were on the foredeck of Nelson’s “Victory”, and they caused huge damage at Trafalgar. Can you imagine loading a 68 pound cannon ball into the muzzle of a hot cannon? Many actions proved the killing power of carronades, and the British Admiralty were so impressed that they replaced long guns with carronades on many of their ships.
The French, and Americans were less rapid to access this new technology, although Napoleon, who was an artillery officer, was adamant that the French navy should have the carronades installed as quickly as possible.
The British equipped some of their ships almost exclusively with carronades, and at close quarters they were devastating and they won some notable victories.
Unfortunately, although they were devastating at close quarters, they did not have the accuracy or range of long guns beyond about 500 meters.
So in the war between the Brits and the Yanks in 1812, the Americans found that all they had to do to win at sea and on the Great Lakes, was for their frigates to remain beyond the carronade range, and shoot their long guns, with many victories, and great frustration of the Brits, who were not used to losing naval battles.
Carronades were commonly installed on merchant ships, privateers, pirate ships, and small naval vessels, due to their relatively light weight, and small gun crew. But the Royal Navy stopped using them from 1852, when breech loaders were the latest new technology being installed wherever possible.
I decided to make another 1:10 scale model cannon. A 32 pounder carronade, the same scale as the previously blogged 24 pounder long gun, to put them side by side for comparison.
It is almost finished. I will post some photos soon. Look forward to squat and ugly.
Some temporary bolts inserted until I get around to making the permanent brass fixtures. And the quoin and bed finished. And the wheel halves joined with brass pins.
The barrel is 300mm-12″ long. It has straight sections, a taper section and several curved sections. Plus several types of bands called astrogals. It would be ideally suited to turning on a CNC lathe, but is much too long for my Boxford. So I am asking around, to locate a larger CNC lathe for hire/loan. If all else fails I will use my manual lathe, but I expect that the finish would be better on a CNC.
I will drill the bore first, and after considering the options, will use the Jerry Howell recommended method, which is to use a D-bit.
Some decades ago I made a table for our kitchen. (cannot find photo just now, will add one later)
I bought the wood from a wood recycler. He removed trees from Melbourne suburban gardens, then cut them into slabs and air dried them.
I recall that I paid about $AUD 1000 for the 6-8 planks. They were about 40mm thick and 300mm wide and about 2.5m long. They were so heavy that I could barely lift them.
I have since learned that they weigh 1.1 to 1.4 tonnes per cubic metre, which is at the high limit of wood densities.
The tree must have been 400mm diameter, because some slabs still had the bark attached to both sides.
The wood has a beautiful dark brown colour, with almost white sapwood solidly attached. It is unbelievably hard, and I struggled to machine it with my thicknesser/buzzer. Also, it was the most reactive wood I have ever worked. When planed or thicknessed it would bend and react totally unpredictably. My 40-45mm thick planks ended up 25-28mm thick and even then they were not totally flat.
But SWMBO liked the table, and it still is the main meal table in out house. One of my daughters requested a similar table, which I made from Gippsland Blue gum, another spectacular dense hard Australian wood.
The ironwood has survived kids dancing on it, steam engine demonstrations, being used as a work bench, not to mention many meals with never a table cloth. And the wood itself is unmarked! The polish has disappeared in places, but the wood itself seems impervious to damage.
To get to the point of this post, I am currently making a 1779, 24 pounder, 1:10 scale naval cannon. Jerry Howell design. About 300mm (one foot) long.
When I was looking in my shed I considered various woods for the carriage-base. I considered some black walnut, which was recommended, but it seemed a bit light in weight and colour. I considered some Australian redgum, which polishes beautifully, and is dense and tough, but it is a bit too red. Some African Odum looked possible, but the figuring is a bit plain. Then I found some ironwood offcuts from the table job, and the decision was made. Ironwood it is.
So here are the initial photos of the carriage parts. They were machined on my metalworking mill, using HSS cutters. I CNC’d where possible.
Watch this space for progress on the cannon.
There are some technical challenges, including deep boring 14mm diameter 275mm deep, making a tiny dovetail in the ironwood, and turning the barrel from 50mm diameter brass.
I took another break from the triple to make this tapping guide…
The biggest problem with tapping threaded holes is taps which break in a job. Sometimes after many, many hours making a part. Sometimes the broken tap is able to be removed, and sometimes it cannot, resulting in a ruined part, wasted time and much wailing and gnashing of dentures.
Keeping the tap vertical at all times during the tapping procedure, and using a sharp tap, suitable lubricant, and appropriate torque, are the keys to not breaking taps and saving teeth.
Usually I do my tapping with the tap held under a spring loaded guide in the chuck of the drill press or mill, and the workpiece in the vise. This method prevents any inadvertent bending of the tap, which avoids one of the major causes of breakages.
But sometimes it is just not possible to hold the workpiece in the mill or drill press and the tapping has to be done freehand, aligning the tap by eye. I am rarely satisfied that the tap is vertical after using this method. Lack of accuracy, and higher chance of a broken tap is the consequence.
So when I saw this tapping guide in “Model Engineer”, and saw the possibilities for its accuracy and versatility, I decided to make one. The fact that much of the machining could be CNC’d was an added attraction. Also the 4 jaw chuck was intriguing. I had seen one made by a colleague in the Melbourne Model Engineering Club, and I was keen to see if I could manage it.
The design was by Mogens Kilde and the plans were published in the August 2015 “Model Engineer”. I made a few minor changes to the design, mainly using thicker aluminium in the arms and flanges. I used stainless steel for the chuck body because that was the only free machining steel which I had in the size. I used key steel for the chuck jaws, again because that was what I had available in my workshop.
The double parallelogram arms keep the tap vertical within the limits of the arm movements. Using a 3 jaw chuck as the base of the unit provides a lot of flexibility in positioning the guide.
I will not comment on the actual building, because that is clearly explained in detail in the original ME articles.
The triple expansion engine legs will be bolted to the base, with 9 bolts each. That is 54 holes which needed to be precisely drilled so the columns are accurately positioned. Each one of those holes needs to have a mating hole made in the base. The base hole will be threaded to accept a stud.
Normally one gets accurately mated holes by drilling through both objects simultaneously, but that was not possible in this situation due to obstruction from the columns themselves.
So the solution?? CNC of course!
The hole positions were known from the CAD drawings, and were entered into the CAM program. The resulting file was too big for my old CNC mill (1997 model), so I attempted to drip feed the information as the machining operation was taking place, but without success. Several phone calls to my expert friend Stuart did not resolve the problem, so Stuart kindly came to suss it out. A couple of hours later he had the drip feeding working as a result of a serendipitous error.
We knew that the largish file needed to be drip fed into the CNC mill, but it eventuated that we had to try to enter it directly, and produce an error message first, before drip feeding it. A bizarre system, originating from the land of Manuel of Faulty Towers.