I'm going through all the preliminary design work for the light pacific I want to build. I've read Mr. Nelson's book with his section on boilers, and still have more questions.
How do you form the "raised" section of boiler? Not sure if there's a name for it. I can't tell if it's a concentric cone or an eccentric bushing of sorts. Is it welded from a rolled sheet to simply match the two diameters of boiler? I have attached an image with a box around the section I'm talking about. It's kind of hard to explain, but for me it's a little harder to figure out mathematically.
Another random one: Has anyone ever heard of someone using a "bottom slotted dry pipe" on their small scale engine? I'm not sure it would give any advantage on a small scale, but my particular engine doesn't have a full sized steam dome. I'll figure it out, but it'd be cool to know if someone's done it before.
Thanks
"We'll cross that bridge once we realize nobody ever built one."
Two ways: as Fred V says: that involves laying out an eccentric cone for rolling from sheet stock; or an eccentric pipe reducer - sort-of ugly but efficient. Down and dirty method would be to use the larger boiler tube, figure the circumference of both ends of the tapered section and cut a dart out of the tube leaving a tab at the large end. You should be able to push the 'opening' together and coax it into shape with a torch, hammer and chunk of steel rod as a buck bar - weld the seam where the dart was.... Unless you are using super thick boiler tubing that will make a suitable eccentric cone.
You didn't mention what scale you are working with for the CP Pacific?? Also, does the boiler have a belpaire fire box? CP was a fan of them for a long period of time with most all of their locomotives.
There a several names for the boiler sheet your asking about. Two common names are "slope sheet" and "gusset sheet". Each rolled ring of the boiler is a "course". The large end gusset sheet course was formed and flanged to fit inside of the larger course around the fire box or immediately ahead of it called the steam dome course. The small end of gusset sheet was flanged to fit over the course immediately in front of it and so on to the front end of the boiler.
Enough useless trivia. Most modelers don't make a gusset sheet as it is pretty difficult to roll with light weight hobby shop equipment. Rolling a 1/4" or 5/16" thick piece of steel, or copper for that matter, into an eccentric cone takes considerable force. Most often the eccentric smaller front tube is adapted to the larger diameter fire box outer wrapper by a flat adapter plate. Then the boiler gusset sheet is faked in with the use of a lagging gusset sheet so to look like there is an actual boiler gusset sheet under it.
There is a book available that describes making a gusset sheet that can be used for either the boiler or lagging. It is reprint of a 1907 book that uses straight forward calculations and illustrations. The book is in the public domain and has been identified as a historical artifact and culturally important so worth while if just for reference to look into our technical past. The full title is "Laying Out For Boiler Makers and Sheet Metal Workers; A Practical Treatise on the Layout of Boilers, Stacks, Tanks, Pipes,Elbows, and Miscellaneous Sheet Metal Work" and can be purchased through used book retailers.
Excellent book! "Laying Out For Boiler Makers and Sheet Metal Workers; A Practical Treatise on the Layout of Boilers, Stacks, Tanks, Pipes,Elbows, and Miscellaneous Sheet Metal Work"
If you decide to go the "fake it in" route, and have two diameters of straight barrel, here is a photo of how it was done on a 19" gauge engine (Swanton Pacific.) then laid over with tapered jacketing.
Incidentally the original Overfaire boilers were real wagon tops (second photo)
Somewhere I have seen a photo of a faked taper that had wedge-shaped support legs welded to it, that the jacket could rest on. Can't find it.
Attachments
Live Steam Photography and more - gallery.mikemassee.com
Product Development and E-Commerce, Allen Models of Nevada
To answer some of the dimension questions, here's my draft erection drawingfor 1.5" scale. I am... torn between 7.5 and 7.25 gauge. I'm in the North East, so the places in Canada, PVLS, and Washukum are 7.25, but everywhere else seems to be 7.5.
I do all my drawings on Onshape, so if you want to take a look as it goes, here's a link.
From your drawing, I see the smaller diameter as 8.4" and the larger as 9.44". The former is pretty close to 8 inch pipe (8.625") but the latter is in between pipe sizes (10 inch is 10.75"). So what are you going to use for that?
I'm just gonna fess up and say I haven't the faintest clue. I'm sure there's some 9" pipe hiding out in the darkest recesses of the known world, and worst case I can do whatever I did for the gusset sheet, be it rolled flat stock or "faked" with boiler jacketing. While my hopes and dreams say to not fake it, I'm not exactly gunning for a performance engine by modeling a "light" pacific.
I'm glad you caught that now instead of me finding out I can't make a boiler to fit my chassis a few years into the project.
"We'll cross that bridge once we realize nobody ever built one."
I doubt that you'll find any 9 inch pipe. However, "Drawn Over Mandrel" (DOM) tube is easily obtainable on the 1/2" outside diameter increment in larger diameters in various wall thicknesses.
If you care to print out the gusset sheet fabrication method from the above book it is on pages 71,72, and 73.
If you go the fake it in route let the smaller tube pass all the way through the adopter plate so that it can be fillet welded to both sides of the adapter plate. That will be much stronger butting it against the adapter plate and one fillet weld around the outside.
By the way the fake it in route will not have any negative effect on your boilers steaming capabilities. The gusset sheet is or mostly is above the water level so if any thing the fake it in route reduces the steam space only slightly. Why a gusset sheet at all? My guess is it was to keep all of the boiler outer shell a much as possible in tension as opposed to bending since steel has much better fatigue life in tension than the back and forth stresses of bending. The thickness of our model boiler plates is so much more proportionally thicker than the prototype that flat plate fatigue is not a problem.
Just for reference are a few pictures of my fake it in route for my 1.6" scale NYC&HR 999 project boiler. The boiler is all fabricated from 1/4" thick copper. I don't know how I would have formed an actual gusset sheet. If there were a gusset sheet it would have extended to the lagging spacing hoop at the rear of the sand dome.
