This week has seen me drawing the domes, stack and smokebox front for 622. These will all be 3D printed to start; depending on how they turn out, I will either use them as they are and fill them with lead, or cast them from Cerro-bend after cleaning up the castings.
Again, OnShape amazed me with its ease of use and accuracy. Check out those fillets at the bottoms of the domes and stacks! To make them, I started with a revolve of the basic dome shape, which extended well into the boiler. Then I created a base for the dome with another revolve on the same sketch, just a bit wider. This, I intersected with the boiler and then unioned with the dome. Then I formed the fillet along the line where the base and the dome met. Finally, I subtracted the boiler again to remove the base. Oh, then I hollowed it out with a shell command, to create a part slightly thicker than the minimum wall thickness at Shapeways.
It took me a while to figure that out, which is why I wrote it down. However, by the time I was tackling the stack, I had the whole operation down pretty slick. Of course, because it’s parametric, going back and changing the proportions of any of the domes is a doddle! You just have to change the original sketch.
Go ahead and make a copy of my drawing and try it yourself. The domes are on the tab labelled Details.