As in modelling, drawing follows the 90-90 rule. The first 90% takes 90% of the time. The last 10% also takes 90% of the time. I’m in to the last 10% of this drawing.
The trouble with brakes on steam engines is you have to remove them before you can remove the wheels. My previous engine, #10, had no brakes, and the one before that didn’t have removable wheels. So, designing the brakes on 622 was unexplored territory. For #622, I plan to fix the brakes to the ash pan, which itself includes parts to hold the wheels in their pedestals.
When I first started thinking about this, I thought the whole brake assembly would come off with the ash pan. However, that would leave the cylinder at the end of a long thin piece of plastic. Long thin pieces of plastic tend to suffer from my clumsiness just when I’m putting the model together for the last time, beautifully painted, the night before taking it to a display.
It is better to leave the cylinder and brake arm stuck to the frame. The natural place to then break the brakes is at the short link that connects the main brake lever with the short equalizing beam, where orange meets red below.
However, then the either the equalizing beam or the link has to be very thin. The join is also right out there in the open. So, after humming and hawing for several days, I came up with the idea of breaking the main brake lever itself. This is a joint that will be hidden from most viewing angles, and both sides of the join are relatively thick pieces of plastic.
The brake cylinder and half the arm can then be permanently fixed to the frame, while the rear brake assembly will be pinned to the ash pan. It’s tempting to print the rear brake assembly with the ash pan, but that’s asking for trouble as I anticipate disassembling the model hundreds of times during construction.
Finally, the front brakes need to be way out there, and will be extremely vulnerable once installed. To help them survive, I’ve added a couple of little nubs behind the wheels on the sides of the ash pan. These are grooved to support the .015″ steel brake rods.
There are a couple of straps holding the brakes up, but I’ve left these out of the drawing. I’ll create them out of brass shim stock when the time comes.