622 Final engine details and a discovery

Despite the glorious summer, I’m still getting a few minutes of modelling time in most days. A few minutes adds up and soon there have been hours, and now I’ve finished the engine part of 622. There is still a short list of details to add to the tender, but an hour’s work should see that completed too.

The equalizing tank turned out trickier than expected. As you can tell from the grey plastic, I printed it on the Mars. However, the first version was not very good – you could definitely see the .05 mm layers, especially on the top and bottom of the print. Sanding it only made the straps less distinct. I tried printing it again at the minimum layer depth, but got some parameters wrong and burned an FEP membrane. So, I went back to .05 mm layers, this time printing the part at a 45 degree angle. The resulting part looks okay to me.

The front brakes are printed together with their equalizing lever and even the block where they hang from the frame. They are held to the ash pan and against the frame with .015″ music wire pull rods. Fitting the pull rods turned out harder than necessary, affording me plenty of time to think about how to improve the design for next time. On the next engine, I will etch the mounting blocks into the frame, and print the front brakes together with the ash pan, connected via a temporary strut. Then after fitting the pull rods, the temporary strut can be removed.

As I was taking the photos shown here, the model caught me gloating and declared “not so fast.” Because I left the rear drivers off, it was reasonable to expect the front drivers to be sitting at their maximum height in the frame, but they weren’t. It turns out that the front driver bearings are bottoming out on the fake eccentrics for the Stephenson’s valve gear. Maybe I should have made the valve gear work, after all.

I have to think about what to do about this. I’d rather not replace the valve gear at this point as the rocker arms are holding the ends of the valve stems. In any case removing the part is going to be more violent than I would like at this stage of the model. I think I will sleep on it.

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