I’ve sort of painted myself into a corner here.
I was about to eyeball sanding an angle on the bottom of a pair of cylindrical capped chimneys with my disc sander to attach to my slanted not the Mik project.
Of course this is complicated by multiple diameters in the cylinder and the need to line up my cap supports properly.
Any suggestions to get a better result?
Bill,
I am guessing you are referring to the bottom of the chimney where it meets the roof. Looking at the pics I am going to assume you have a table saw in your shop.
Cut a piece of 2 x 4 (or metric equivalent) to fit the length of the short small diameter center section. Cut a ‘V’ notch to set the chimney in (keep it as high off the table as possible). Use a scrap strip with a screw to secure the chimney in the ‘V’ block.
I have a sanding disk (10" dia) for my table saw. Adjust the ‘T’ square for the table saw to the desired angle and slowly sand the base of the chimney to the desired configuration.
Hope my description gets the idea transferred.
Bob C.
Or just drill appropriate holes through the roof remembering that each smokestack would have a cone shaped duct on the lower end to vent the smoke from the locos still under steam. 
I feel like such the newb, not getting my terminology correct… smoke jacks added to list. You’re right, Rick. There’s not many fat smoke jacks on the web.
I found a fat smoke jack prototype but had to go to Taiwan for it. Built 1922.
Bob, My table saw is miniature and can’t do Arbor cuts, but my sander will allow me up to 45degrees off vertical and much more laterally. I suspect my roof angle is just off 30 degrees. I’ve made a rough wedge to see what it might look like though.
David, I found putting the windows in the ancient floorboards I sourced my cedar from for this build, splinter at the sight of a saw or drill. Big blowouts came even with the pin nailer. It does ok with carving tools. I suspect my math skills would need refreshing to carve an appropriate oval. Though the thought of cutting the smoke jack in half and gluing to both sides did cross my mind.
Now that I’m smoke jack aware, I’m finding quite a few roundhouses without smoke jacks too. It appears many roundhouses just vented through the upper windows.
Now I’m wondering if a smoke jack actually adds any pizzazz to this model…
I vote “yes.” It adds a bit of visual interest that breaks up the lines of the building. But then, I lack both your talent and your tools, and, if it were my project, and I were stuck, I’d probably leave it off…
Still, were I attempting to get this stack to stand upright on a similar project taking shape on my lanai, I would tap a hole in the dowel and a hole in the base. Then I’d cut a bit of metal rod, shove it in the base, put the stack on top, and start kneading putty or epoxy resin between the stack and base. Then I’d wiggle the stack until it looked upright, let it all set, make it fast with CA glue, and file away any residue.
Eric
Just an FYI Bill. This round house is/was a coach repair shop for the B&O in Baltimore, not an engine facility. Now the museum.
Wow David!
What was the purpose of such a high ceiling then, if it wasn’t to funnel out smoke?
Snow load. And age finally went against it in 2003 I believe. What your pic shows is after the rebuild.
Edit to add that heat in the summer would rise for better airflow and the B&O was in a stage where opulence was the word of the day.
your roofridge itself is a giant smoke chimney hood.
so, tecnicaly you don’t need smokestacks.
reasons for putting smokestacks:
That was my thought too. And I agree with Korm’s reasons why you could add it if you wish.
I will 3rd that …just open them pivoting windows up top.
UPDATE
Thanks for all the ideas. It’s been interesting to find how this smoke Jack has really slowed down the build. After all it’s just a chimney or 2…
So far I have been successful in sanding fingers down to the quick 3 times🩸and interestingly @Devon_Sinsley it feels just like a paper cut, only wider.
I like the idea that the shed can work without smoke jacks but we kinda also like the chimneys. The roof is Massive and needs something to distract from that. Thinner shorter smoke jacks got lost in the large roof so I returned to trialling the industrial ones.
Square Bases
Herself came out and said, “I can see you’re overthinking things again” then pointed out that the prototype pictured above actually had square bases then suggested I just make a bigger rectangular wedge properly angled to see how it might look.
I think it is an ok compromise and Woo-hoo! I got to make plywood!
But I think I owe her dinner now.
The cubic base has the advantage of not needing a cowling or special curve cut shingles. It is the length of 1.5 shingles and the width of 3 and will allow me to properly place shingles if the smoke Jack idea flops.
Painting
They received a coat of primer and some grey paint.
But it didn’t quite look right… too heavy; too concrete? I dunno…
I was initially heading towards a black matte paint but thought if this looks heavy, maybe I should go the other direction.
So it got another “brighter” coat of paint and I chamfered the edges make the assembly look less massive.
They’re less heavy looking but maybe they’re too eye catching?
EDIT ADDITION
*Well, I’ll have time to think about this… as yes, I do owe Herself dinner.*
Story around the B&O Museum was that the original architect always wanted to design a cathedral.
I can confirm, having worked there in the summers, that the airflow up and out of the cupola worked.
A nice distraction would have been an octagon cupola in the middle of the roof with working industrial center pivot windows (since you know how to do them now quite nicely). Then I suppose an Ozark Miniatures rooster weather vane on top of the coopola if you can find one!
Only a thought and the smoke jacks look excellent!
