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Discussion Starter · #1 ·
Here's a few photos of a coal-fired boiler project for a Roundhouse Billy. It's taken me a long while to get started on this, but I've got high hopes that it'll get done. One cause of delay had been understanding how to configure properly a blast pipe. A recent parallel project to convert a Roundhouse Billy to alcohol firing provided the insight and confidence to go ahead with this one.

The first photo shows the setup to silver braze the flue tubes and firebox shell to the firebox tube plate. Those are firebricks. NEVER use regular bricks for silver brazing because of the high temperatures involved. Regular bricks can explode at these high temperatures.

The firebricks are stacked up to support the assembly and to shroud it to reduce heat loss. Firebricks will reflect heat, and they will glow red hot when the torch flame plays on them.

The ends of the flue tubes rest on a piece of ceramic insulating material, which keeps them from dropping out of the tube sheet as the copper heats up. The ceramic sheet also blocks the lower ends of the tubes to keep cool air from flowing up the tubes and cooling the area that's being brazed.

I use two torches. A propane torch (pointed right at the workpiece in the photo) heats the whole assembly, and a hand-held MAPP torch (the yellow gas bottle) provides heat right at the spot to be brazed. The "Contadina" tomato can keeps the MAPP bottle upright and in one place. The can is attached with screws to a board that's clamped to the workstand. The propane bottle is hose-clamped to a stand made from an old floor lamp with a heavy weighted base. With two torches going i don't want either one of them to come adrift.



The next photo shows the assembly after pickling.



The last photo is the throat plate that was formed out of 22-gauge copper sheet. This was my first attempt at riveting, and I've got a lot more to learn. I had to silver braze this in about five different sessions, with pickle and rinse between each, before I felt that the joint would be leak tight.



Next step is to fit the firebox outer shell, rivet it to the boiler shell and throat plate side flanges, and silver braze the riveted joint.

Steve
 

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Steve: very nice work, especially flanging that throat plate. Boilermaking is a lot of fun, isn't it?

Looking forward to more, Bob
 

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Steve,

You're off to a great start on your boiler. I like the hearth...couldn't do that outside over here now....too cold! If I can make it out to the NSS this year, I'd certainly like to have a look at it.
 

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Steve,
what reference material are you using to show you how to properly do all this. Or the gurus at a club/website are helping u out (I will be building something similar in the near future).
I know people suggested a few books, just curious on what your using.
 

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This is going to be a very interesting thread. I can not wait to read your next installment!
 
G

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For your boiler-building notebooks:

100% of the joint/seam strength in a silver soldered copper model boiler is derived from the silver solder. The only mechanical fasteners (rivets, screws, etc) necessary are those which are needed to hold the boiler components together while assembling or silver soldering.

A properly prepared and executed silver solder joint is stronger than the copper parent metal.
 

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Discussion Starter · #7 ·
Andrew,

Get a copy of K. N. Harris' "Model Boilers and Boiler Making". It has very complete design and construction info for copper boilers of this size. There's a LOT of design data and calculations but work through them to really understand what the constraints and requirements are for a safe and successful boiler. Harris has a lot of practical advice about the design and placement of the various boiler fittings as well. Several months ago Chris Scott posted in this forum the link to Henry Greenly's 1903 book "The Model Locomotive, Its Design and Construction", and it contains the same boiler design calculations as Harris. I wonder how long the same rules had been around before Greenly published them 105 years ago?

Read every resource you can find and do some "google" research on the internet, especially for the smaller ride-on scales. Kozo Hiraoka's books and articles in Live Steam magazine are gold mines of tips and techniques. This forum has also had boiler fabrication postings with good photos that show how others have done things. Coal-firing has its own requirements (and problems) but all successful boilers for any fuel will share common features.

For a long time before cutting any metal I pestered the experts about design details and design formulae. Shamelessly at steamups with flashlight and ruler I would measure fireboxes, grate areas, and flue tubes (diameter, length, and number of), and then head back to Harris' book to see if the numbers corresponded to his calculations. I must have "finalized" my own design about six different ways in the past few years. For excellent advice about silver brazing techniques I will credit a couple of generous experts in our hobby and the writings of Kozo Hiraoka.

I'm no expert but will try to help as best I can.

Steve
 

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Discussion Starter · #8 ·
Curmudge,

I concur with you about the rivets. The fit between the throatplate and boiler shell was not perfect, so I used 6 rivets to try to pull the mating surfaces together. Otherwise 2 or 3 rivets would have been sufficient to hold the throat plate in position. Next time I will spend another hour to make sure the fit is better. Then fewer rivets would be needed and the silver brazing operation should go a lot quicker too.
 

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Thanks, I am doing the same on here, I think I asked the boiler making question about 6 times now :p. I belong to the tradewinds and atlantic railroad club (http://www.livesteamers.org), 7.5" and I am pulling info from the 7.5 gauge scale too. Eventually I will start to poke at it and finally build my first working version.
 
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Well we use the rivets and fasteners we think we need to get the job done. Many years ago my first boiler had a couple of hundred fasteners which I know now was for most part a complete waste of perfectly good rivets.

Andrew, be careful what you try to adopt or are told to adapt from large scale practice. The "language" and techniques of live steam vary from gauge to gauge and what might be considered good or required practice in large scale might not suit the limitations and requirements of Ga1.
 

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Discussion Starter · #11 ·
Progress update with two more photos: riveted and silver-brazed the firebox outer shell to the boiler shell and throatplate today. A couple of the rivets just didn't peen over and cinch up as expected, so it took a lot longer than planned. One of the rivets sort of skewed sideways and made the hole larger. Then even a new rivet wasn't held captive so it wouldn't peen over properly either. Finally I filed a tapered pin from a length of #10 copper wire and gently drove it into the hole. Peened it over just a little after silver brazing and left it at that. While wrestling with the rivets of course I kept mashing the throatplate out of shape. Fortunately the copper was annealed from the brazing heat, and I could reform the copper back into place. If I had taken time to set up a proper bucking iron and support for the boiler it probably would have gone better.
The good news is that the brazing was done in only three passes. Once for the external side of the joint, with the boiler vertical, and twice for the internal side of the joint - twice because the boiler was lying first on one side and then the other. Here are the photos:




I should mention that one "tool" that's been indispensible is a length of ABS pipe that fits snugly inside the boiler shell. I slip it inside the boiler shell whenever I have to cut, file, or drill. The copper is very soft after it's annealed by high brazing temperatures, and the plastic pipe keeps the copper shell from collapsing while it's being grasped or held down on a work surface. Without the plastic pipe "tool" I'd be working with an unevenly egg-shaped boiler at best. Needless to say I discovered the ABS pipe trick AFTER I had done some cutting and filing on the annealed boiler shell, followed by, "Son of a gun...what happened to the boiler?..."

That's it for now. Before I install the front tube sheet and fit the flue tubes and firebox I need to do some measuring and checking for the various fittings. I thnk I'd better drill all the holes before installing the the flues and firebox while I can still use that ABS pipe to support the boiler shell.

Steve
 
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Something that I find very handy for accident (and heartbreak)-free hole drilling in copper . . . a Unibit. I don't know how I got along without one. Since your copper appears to be a bit on the thinnish side, and the Unibit takes some extra pressure to start, I would spot bushing holes through with a conventional 1/8" drill bit first, then follow with the Unibit.
 

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Re holes in boiler shells, I always mark out and machine the holes with the copper in its "as drawn" state, it is much harder and easier to drill, for large holes I use " Q-max" cutters, When riveting I anneal the rivets first, makes them easier to form.
David Bailey www.djbenginering.co.uk
 
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Re holes in boiler shells, . . . "Q-max" cutters

David,
Over on this side of the pond those are known as "Greenlee" chassis punches. Very nice to have, hard to find used, very costly new.
C
 

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A quick search on the net turned up Newark electronics as carrying these hole punches.
 

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Discussion Starter · #16 ·
Time for an update. Today I silver-brazed the front tube plate and flues in the boiler shell. Actual brazing step took about 10 minutes, but it took several hours of prep work to get to that step.

Last weekend I started preparing by trimming the parts here and there and making things square. Then the various bushing locations had to be figured out and double-checked. Then I discovered that a couple of dimensions came out different than planned, so I had to rethink how the firebox would mount to the loco frame. By this time I knew that the brazing step would need to be postponed to this weekend.

"Thank you" to Curmudge for recommending the Unibit. I bought one last week, and used it today to bore the holes for the bushings. Worked like a charm. I've always dreaded boring large holes in thin copper with a standard twist drill. Never seems like it's under control and probably isn't, because the holes never seem to come out in the right places. With the Unibit I have seen the light.

Here's a couple of photos of today's work. As you can see the firebox will be deep. The top of the grate will fit against the lower edge of the firebox inner shell. A thin-gauge stainless extension will enclose the grate and lower part of the firebox, and the ashpan will attach to it. The lower edges of the firebox outer shell are planned to be level with the top of the Billy loco frame.

Next tasks are to fabricate the bushings, drill for the firebox and crownsheet stays, and fabricate a blower line to fit from the backhead through the boiler to the smokebox.





Steve
 

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Mighty fine looking boiler!
Good work and workmanship.


(Please don't heat it with a propane torch like those fellas at Halley Base in Antartica!
)
 
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With the bushing holes drilled first you can turn the bushing spiggots to a press or tap fit in the holes and the bushings will be self-jiggiing while silver soldering. For anyone who is unfamiliar with the term "jigging", a jig is a construction tool, usually a machining or assembly aid or guide which holds parts or assemblies in place while another operation is taking place. In model engineering it is not uncommon to have to make jigs, and every once in a long while one needs to make a tool, to make a jig, to make the final part. ( . . . no one said it was going to be easy!)
 

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Steve,
cool (and hopefully hot!) project. I'm currently collecting bits and pieces of copper for a boiler project for next year, somewhat along the lines of what you are building. It will be nice to see your finished boiler, and find out what you learned along the way.

Thanks,
André,
Norway
 

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Steve: Coming along great. Looks like the hard work is almost done. What silver solder are you using?

Bob
 
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