Its time to start in on building the Diesbar paddle steamer engine!
I've been wanting to do this engine for quite a while, it has a very interesting motion and mechanism. The engine was designed/built by John Penn & Sons in 1841. It was later moved into the Diesbar in 1884, and is still running in that ship today on the River Elbe in Germany. The engine is an oscillating type, which allows it to be quite small and low to keep the weight lower in the hull. The crankshaft is at the top, and is directly connected to the 12.5 foot paddle wheels on either side of the hull at up to 38 RPM. It has a bore and stroke of 24.5" x 27".
The valve gear that Penn designed is quite interesting, with a sliding arch link in the middle that looks like a Stephenson linkage, but it is there to transmit the up/down motion from the eccentric to and arm running around the side of the cylinder to the steam chest, with one end of that arm sliding in the slot in the linkage. That way the oscillating motion of the cylinder does not effect the valve motion at all. For reversing, the eccentric is a slip type disc, it can rotate partially on the crankshaft with stop blocks at either end of its travel - the eccentric is rotated one way for forward, the other way for reverse. Unlike some other slip-eccentric engines, there is no direct control of rotating the eccentric. Instead, the engineer can uncouple the linkage from the eccentric strap arm, and move the valve himself. There is also a throttle valve for each cylinder. That way, the engineer can uncouple the links, move one or the other as needed to start the cylinder in the opposite direction, and open one or both throttles to start the engine. As it starts to rotate, the stop block for the other direction will come around and push on a pin on the eccentric, so that it now rotates with the crankshaft in its new position. The valve links are sprung back into the holders on the eccentric straps, and the engine continues in the new direction normally. There are what look like the leaf springs from a car that pull on the linkages to keep them in the holders, unless the engineer pulls them out. Quite a clever system, but it takes some real skill by the engineer to know which way to move which link to start the engine in the new direction!
This excellent video from Youtube shows the ship and the engine being run:
With a lot of help and pictures from Michael on this forum, and reviews by one of the workers on the ship that he knows, I was able to draw up the engine in CAD.
There is a book on building the engine written some years ago, but that version is much simplified - I wanted to do a model that was as true as I could make it to the real engine. Hopefully this model lives up to that standard. I drew the engine at full size, then made a scaled down copy of it so that the cylinder bores were 2", which keeps all the parts in a size I can make on my lathe/mill. Also it worked out such that the leftover right angle pieces of brass I have from building the Ohio crane model will work for the ange sections on the upper framework. Michael also got me plans for the paddlewheel, I would like to make one or both of those, will tackle that after the engine.
This morning, I got started cutting metal. The cylinder parts are being made from sections of a 2-3/4" brass round bar, plus a piece of 7/8" bar for the pivot trunnions (which also are the steam/exhaust passages).
The passages go from the trunnions, and around through the inside of the thicker rings on the outside of the cylinder to the steam chest. On the real engine these passages were cast in place in the cylinders. For the model, I am going to make the center rings and trunnions as subassemblies, then slide them onto the cylinders from the lower end. It is critical that the trunnions are in line with each other on either side of the cylinder, or it will not rotate freely. So, I will take the medium-length rods shown in the previous picture, drill/bore through the sides for the trunnions, and silver solder the trunnions to the rings. Then I can mill in the passages, with steps either side for covers to seal up the passages again. Then will bore out the center of the rings/trunnion assemblies, and slide them onto the cylinders (after the cylinders are turned). The other thinner discs in the picture will be the top/bottom covers on the cylinders. The full size engine has the cylinders cast/bored as blind holes, I will through-bore and cap the bottom of the cylinders to get the same look. Its a lot of steps, hard to describe it all but it will be clearer as I proceed.
So, on to the parts! First steps were to clean up the sawn ends of all the bars. The top/bottom covers were easy, held in the 3-jaw chuck with the jaws reversed. Then moved on to the medium length bars. Perfect chance to try out the new steady rest I made the other day from a piece of aluminum pipe section and some roller blade ball bearings. Given that the reversed chuck jaws are fairly shallow, this gave enough stability to be able to face the ends without worrying about the bar being dislodged and falling out.
The sawn ends are not perfectly square, so with the bar straight in the chuck one or two jaws might have the bar fully seated,
while at least one has a gap:
As you can see, not a lot of engagement for several pounds of bar hanging out! With the steady rest in place, I was able to adjust the arms till the bar ran true and all three bearings were in contact for the full revolution. I adjusted the arms initially with them right up near the chuck, then moved the rest out to be near the outer end of the bar.
After trimming both ends of the shorter bars, I started in on the longer ones for the cylinders, with the rest moved out farther. The two ends of each were trimmed true and to length,
then center drilled so I can take the rest off and switch to supporting it with a live center, to turn down the outsides of the bar ater.
The steady rest is working very well, well worth the time to make it! Next I need to turn the trunnions to size/shape, with the flanges at the ends and the ends bored out - there will be an o-ring fitting that goes inside the trunnion ends to connect to the other piping. Then I'll set up to drill through the sides of the ring blocks to take the trunnions, and then be ready for silver soldering.
