The traction engine is starting to take shape, but the Burrell crankshaft looks like it needs some thinking about.
The issue is the clearance between the top of the firebox and the shaft. OK, this is not the correct shaft yet as I haven’t finally reamed the bearings to size (4mm). However, it demonstrates the issue.
The actual issue arises because of the way in which I created the boiler and firebox as separate parts. The boiler fitting into the firebox means that the firebox sits above the top line of the boiler.
The crankshaft needs 6mm of throw on the crank to give me 12mm of stroke on the engine. This means the crank and conrod big end need to clear the top of the firebox.
Looking at the bearing blocks, I think I’m going to lift them slightly in the hornplates/tender. If I then chamfer the top of the blocks I think they will still very much look in keeping with the design. I would like to maintain the centre alignment of the flywheel and cylinder, but I think I probably need to see if this is possible within the proportions of the cylinder block. It wouldn’t be a complete design failure if they were not aligned. I will just need to be mindful of the clearances of the sliding joint on the conrod and clearance to the housing.
The engine is starting to take shape and is a good match to the drawing that has inspired it. I cannot say that it is perfect scale, more a stand-off scale. But sat on my desk it is a very rewarding model. The next step is to make up the Burrell crankshaft and see how it starts to fit together. Then I can go back and remake the bearing blocks.