the crankshaft
I wish I had more to report on, too busy finishing off the rest of the basement / train lounge.
The latest thing I am working on for the Shay is the crankshaft. I have been dragging my feet a little because I was not exactly sure how I was going to do it. I purchased a couple PSC crank shafts to ruin, I mean experiment with.
The PSC crankshaft is the correct size but I needed to get a spur gear mounted to it. The spur gear has a 0.0625" bore and the PSC crank shaft has about a 0.080" shaft OD. I could have attempted to drill out he spur gear but I would run the risk of it being off center, besides it did not solve the issue of mounting it. Brain Bond took a Bachmann shay crank shaft and spliced two together to make a 3 cylinder model, so I thought about using his method, but I didn't what the journals to be as big as there were going to be once I made brass bearings for them.
In the end I decided to cut the crank shaft up into pieces and take advantage of the resin prints ability to resist heat and make a solder fixture to reassemble the crank shaft.
The first step was to saw out all the areas were the crank shaft main journals were, leaving the rod journals intact. I then designed drill jigs to hold the pieces while I hand drilled new shaft holes. Resin cuts really easy so to make the drill jigs stay accurate I lined the holes with brass rod, steel would have been better but these are not production jigs. The jigs worked great and I had perfect holes in every part.
here is the eccentric drill jig. one half of the jig holds the eccentric, guide pins keep it aligned.
the crank journal jig required two different ones because one of the three journals has an eccentric mounted to it. The crank jig has an ejection hole in one end so I can push the part out of the jig. these jigs are tight to keep alignment and without the ejection hole the part would never come out. A piece of wood is used to keep the crank spread when drilling
with all the pieces cut and drilled I now had to put them all together. I used a 0.0625" brass rod as the main shaft. I designed a fixture to support all the parts in places so the spacing and orientation is maintained. Resin parts do not melt with the soldering iron so I soldered the crankshaft together on the fixture. I coated the shaft with TIX flux and used a 40W solder iron to quickly solder all parts and the universals to the shaft. For now I am leaving the main shaft run through the crank journals so I can test the final assembled drive. Once the drive passes test I will saw out the shaft for the main rods, this way I will know if any rough running is caused buy the shaft being twisted or not.
