Crank Shaft
10.03.2004
The crankshaft is made from a single cast part. It was manufactured using the sand casting process and is made of GGG, weighing around 16 kg. The material mixture was also alloyed for use as a crankshaft. After a friend had pre-turned the shaft end on his machine, I was able to clamp it on my small Weiler lathe. The tailstock crank was already protruding into the brickwork. This allowed me to finish turning the outside of the crank webs. Since the shaft was to be ground later, I pre-turned the base bearing seats to a diameter of 34.5 mm with an additional 0.5 mm.
Next, I clamped the crankshaft onto the milling machine using a dividing device. After determining the best use of the cast part, I was able to finish milling the flat surfaces of the crank webs.
Now came the most difficult part of the job - the two crank pins. To do this, my friend Dieter and I first made an auxiliary device for eccentrically clamping the shaft. Two thick sheets (40 mm thick) were each provided with a slotted hole to accommodate the shaft ends and two eccentric centering holes. After precise alignment, the sheets could be fixed exactly to the shaft ends using an M10 clamping screw. The shaft was then clamped onto a large lathe using the centering holes. After precise alignment, turning could begin. There were two difficulties: The shaft now rotates unbalanced around the crank pins - 16 kg with a crankshaft stroke of 102 mm! However, this was not a problem due to the solid construction of the lathe and the relatively low speed of 63 rpm. Secondly, we needed an extra long turning tool because the cast-on counterweights had to be bridged in addition to the stroke of 102 mm, i.e. an eccentricity of 51 mm.
It works! After a few hours of adjusting, thinking, measuring and discussing we have the crankshaft turning (thanks again Dieter).
I then took the shaft to the crankshaft grinder. Since I want to install the machine in a steam boat later, the precision of this component was very important to me. It was worth it, I had no problems installing the shaft in the base bearing, since the shaft is exactly aligned.