Can someone elaborate on how to lay out the jacket sections for the tapered parts of a boiler jacket? My only training at this kind of tapered sheet metal work was to make funnels, and to use the same procedure on a locomotive would require a rather large drawing board. There are a number of locomotives that have lost their jackets, with the sections discarded rather than saved for patterns. Some have a sister engine with the jacket still present for measurements, but others do not. Are modern computer programs useful for this? How did the old timers do it?

Also, the sections, where fastened together, were usually riveted rather than secured with common sheet metal seams. Any helpful secrets here?

I don't know how this was done in days of yore, but I know how mechanical engineer Rod Crawford did it for PM 1225. Rod had the engine's Form 4 calculations in the form of an AutoCAD file, including a general layout of the boiler. To the electronic drawing of the boiler barrel he added the thickness of the insulation (variously 2 or 3 inches as indicated by the blueprints or extant studs) and created new drawings of the sheet-metal jacket, with seams at the appropriate points, with overlaps or allowances for lock forms as needed.

I think the drawings were printed out in segments on a large flatbed plotter and glued together, but they could have been printed out in scale and enlarged by hand onto carcboard patterns. The cardstock patterns were test fitted on the actual boiler to locate holes for the studs, and then the metal was cut. This approach saved a lot of fussing with the conical segments. For the firebox segments we may have just fitted the patterns onto the boiler itself.

Layout for Boilermakers, which has been reprinted has a description on how to layout tapers both eccentric and concentric. I suspect that you could find it in a geometry text as well

Working on a reduced scale drawing has to be done. Mostly just geometry involved. But a computer drafting program would ease the pain. AutoCad is expensive and can be time consuming to master. General Cadd Pro is cheaper, and intuitive in its commands. It does not do rendering, dithering, and three dimensional modeling stuff but is well suited to most drafting needed by the preservation community.

After the scale drawing, the actual size metal, or cardboard templates can be done on a shop floor using trammels for the radii, and generally following and expanding the reduced scale print.

Bob Kutella

Why not just hire a professional? A good sheet metal man can make a jacket in a couple of days. If you want riveted seams it will cost you more, or the shop could cut out your sheets while you do the drilling and riveting. You might surprised how quickly it can be done and how little it costs. Let the person doing the job know of any special requirements; most will be glad to work with you.
It seems to me that many in the rail preservation field ignore the trades. Many of the things we do on this equipment use skills that the people doing it every day have spent years developing. Why re-invent the wheel?

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It's a simple piece of geometry called a scalene cone. I sent Bob a copy of how to solve it and make a pattern from an old Audel book I have on plumbing and steam fitting.
Roger Mitchell
Master Mechanic
Fort Collins Municipal Railway

Roger,

Would you mind sending the same info to me? I am still working to get a jacket cut for our Georgia Northern 107, but there are no companies locally that have done this sort of job in probably 50 years or more. One local company wanted in the low 5 figures to measure, cut and install the jacket, mostly because they have never done a steam locomotive before.

I have measured and rechecked all the basic dimensions of the boiler including the various lagging thicknesses we need to account for (and including some dimensions from sister S&A 750) but the sheet metal company in Alabama that is willing to cut and roll the sheets wants me to provide them with the necessary sheet dimensions. They want nothing to do with the engineering. Thanks.

If you can handle it in MS Word format I can email it to you in an attachment. Otherwise, I can convert it into PDF or JPG also. The whole thing is about 1.5mb. Just need your email address.
Regards
Roger Mitchell
Master Mechanic, Fort Collins Municipal Railway
n0mcr@netzero.net