So far, 622’s boiler remains a pair of nicely formed cylindrical sections, joined by a skanky tapered section that is more putty than substance. All that sanding gave me loads of time to think, and to lament the fact that OnShape’s Sheet Metal Model feature doesn’t extend to cones. As I was shaping, and wondering about how to lay out such shapes, a treatise about which I’m certain I saw in an Audel’s handbook in my parents’ basement, I realized I’d been foolish.
Even SketchUp approximates most circles with many-sided polygons. 20 sides is generally thought to be pretty good. So, why not start with a pair of 20-sided polygons and create a Surface Loft between them? Then, the loft will be 20-sided, rather than properly round, and a sheet metal model can be constructed. It appears to work!
I may need to play with the Sheet Metal Model parameters to get the lengths perfect. But this is miles better than trial and error fitting a paper template.
Pembroke:87 
Rene – There’s an NMRA Data Sheet that outlines the math behind tapered boiler courses. A friend wrote a little program to print out the tapered section on a computer, which I then transferred to brass sheet for my model of CPR 136
Jim Little, MMR
Ooh! Good to know.
Thanks Rene for yet another reason to keep plugging away on learning onshape.
I’m going to suggest you take this idea one step more….
Import the drawing into your Circuit and have that cut the styrene for your boiler course! And could you cut half “etch” lines to mark the bends?
Craig
Yes, using the Cricut to cut this part would be a doddle. I don’t think I would bother with the fold lines, however; it’s easy enough to bend the plastic with some hot water.
I’m enjoying this build immensely. Did the last taper fail?
SketchUp has an neat tool call “Follow Me” so these shapes aren’t too hard. YouTube is your friend here as a lot smarter designers have paved the way!
I’m not calling it a failure yet, Neil; I may hit it with primer tonight.
I found the follow me feature in SketchUp introduce artefacts on anything that wasn’t simple, although I’ve not used the feature ina few years.
Has SketchUp added sheet metal models?