I have always wanted to cast a crankshaft as an experiment to see how difficult it would be. There were some problems that surfaced but nothing that could not be fixed. I was amazed how far cast iron would bend before it would break.
I found this very interesting, thank you. I can't cast iron, yet! But this video will go a long way to convince me to try. Are you going to use one of the cranks or were they just as you say, an experiment?
I do plan to make a large model steam engine in the future so the crankshaft experiment was the first step along the way. It will be great to see you trying to melt cast iron in the future because you will another metal to use in the future. Here is a very interesting video machining cast iron crankshafts in Pakistan.
The thing that got me into casting was a connecting rod for an old chainsaw. It was aluminum with bronze/ brass bearing races. It worked, cut a few limbs and gave it back to the owner. Never heard how long it lasted.
I made a crankshaft pattern and poured a couple of cranks when I started the aluminum SBC. Before I got distracted by the Austin I was building a crankshaft grinder with opposing chucks so I would not need to have the five centers that were necessary for the original 41L40 crank which was machined from bar stock. This example has hot tears and shrinks, but was good enough to be my test piece for the grinder. I couldn't find the pattern, but this is the follow board for it. In the lathe, and then I think some experimentation with the offset pouring basin.
That pattern would have taken a lot of time to make. How much iron was needed for the casting and gating?
Since it was a test of the offset pouring basin, and I shook it out hot, I buried it in ash to cool slowly. I took the picture before blowing the ash off. Here is a better view of the runner and gates.
Here's the pattern. I don't remember it taking very long to make. I had the measurements from the one I machined from the solid bar and added the shrink over the seven inch length. Adding the draft with Bondo took more time so it would draw. The number two and five main bearings are between counterweights and lead to a difficult draw. I cast two in Petrobond, and one in a baked linseed oil mold like I used for the Indian heads.
Somewhere I saw cast air compressor cranks that had a small bar connecting the two throws opposite of the rod journal. I assume this was to help with distortion.
I've seen the linking bars used even in some forged cranks to keep things straight. It's easier to machine them off later than try to straighten a bunch of bend shafts.