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My first Boiler build

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I am researching info, plans and materials for my first boiler build.
I have read Stan Bray's book "Making Simple Model Steam Engines", and K.N. Harris's Boiler book, among others, and everything I can find on the subject. I've gathered all the plans I can find and looking for the best features of each type.
Today I went by my local scrap yard, and the biggest copper pipe I could find was 1 5/8". I bought a 3 ft. piece.
I was thinking of building Stan Bray's #5 double tube boiler. Re-reading the specs for #5, I see he used 22mm pipe. As my pipe is just over 41 mm., I was wondering if it's big enough for a single tube boiler? It is .060" wall thickness.

Hi chucketn, there are few things to be aware of before you start your boiler, in particular you need a complete design with thicknesses for all the parts.  I am not sure what background you have to help you with the detail, but I feel the books you mention, while full of good valuable information, and well worth reading, but tend to point to the direction of what can be done, but do not necessarily  include complete designs ready for construction.  If you are a member of a club, a talk with the boiler inspector before you start is a good idea.  I would suggest that you at least purchase a plan of a recognised design.  Or perhaps one of those PMR kits that at least two forum members have on their list.  There will probably be build logs when they start, but there is currently a world wide shortage of round tuits, and they are waiting for their orders to arrive.  Perhaps you could encourage them by being the first to start.

Many of the available books give what is known as the thin shell formula for a cylindrical shell.  Well known and easy to derive from first principals but it has specific application.  It is for thin cylindrical shells under internal pressure.  It does not apply to external pressure such as any flue tubes through your boiler.  And it certainly tells you nothing about the ends of the boiler, or how to design the bushes for your fittings.  Flat ends are always the weak point to design, and any departure from simple cylindrical or spherical shapes introduces stress concentrations which require specific design consideration.  And even for the shell, the allowable stress varies with metal temperature which is also not so simple to determine.  A design that is recognised by a club inspector overcomes most of the issues.  It is also worth obtaining a copy of the miniature boiler code used in your country, and checking your proposed design against the code before you start.

You did not say what size engine you are thinking of powering with the boiler, or what firing method.  Your tube is about the size of my first boiler, similar to the commercial Mamod models most of us have seen when we were young.  It will be adequate for a small engine with minimal load with a Meths burner.

For that small size, in this country, there is a sub miniature boilers code.  It seems on one hand a bit conservative compared with some, particularly in some specific details which may not apply to your layout, but covers most small simple designs in a simple manner.  At the end of the day the hydrostatic test, and steaming test are the final proof, but best to avoid disappointment but starting with a recognised design.  Particularly for the ends and flue tubes.  And buy or make a good safety valve.   A simple pot boiler is not too hard, even with a few water tubes underneath to increase the heat transfer area, so I would encourage you to keep at it.  With a good design to work from, the basic metal forming, turning of bushes and silver soldering are not too difficult to tackle.

Oh, and while you are doing the searching, start by making a hand pump suitable for pressure testing.  It is not only required for the initial hydro test, but all codes require periodic re-testing, and this is so much easier if you have the equipment.  And when you complete the soldering, you will be anxious to get started.

Looking forward to your build log.


There is no 'club' in my vicinity, (E. Tennessee, USA) that I know of. I'm on my own. As far as plans/designs, I thought Stan Bray's designs were recognized. That is why I bought his book.
This boiler will be for my own use, no exhibitions, no public steaming. I plan this first boiler (might be a second...) to run very small oscillators I've built and maybe a Jerry's Beam slide valve built as a team build on HMEM several years ago.
I'm still looking for plans for a hand pump I feel I can fabricate. I have found several, but not real confident in my ability to make them. Funds are tight, so no kits...

There is a live steam group near Cleveland (TN) and I heard rumors there once was an association of stationary engine builders in Oak Ridge, but I could never locate them, and even so, that's still not in your vicinity.  I won't get into "Code" issues but generally speaking, in Tennessee, the Inspectors aren't interested in you.  In our club (almost 100% welded steel boilers) we make a show of strong self-regulation and regularly invite the state inspectors to visit us.  They appreciate the tip of our cap, but to the current staff we don't represent an imminent danger to 'Elf & Safety, at least on account of boiler operations.

I've built copper boilers from 42mm to 6"OD and for starters the .060"/16ga wall of your tube is plenty thick for steam pressures of up to 100psi, the approximate maximum design pressure for silver-soldered copper.  The problem with a 40mmą tube, in a locomotive type fire-tube boiler, is steam space.  Once you get a flue or a few stuffed in there, there's not much space left for steam and it will go out of breath quickly.  That depends upon the size of cylinders it's asked to power.  However there are all manner of creative things you can do to design a boiler for display steaming using the tube you have but it would probably need to be a marine or stationary power boiler type.

One could build a "Yarrow" type boiler using a triangle of three tubes, connected by multiple flues, with the uppermost as the steam collection space.  In Gauge 1 live steam model railway practice, where the typical boiler OD is 2" or slightly greater, the most basic boiler is the "Smithies" type where the fire tubes simply loop out of the bottom of the barrel.  One such boiler of 42mm OD would struggle to produce enough steam for continuous running, but two or more tubes lashed together might do the job.  In the last 20 years or so there have been a number of advances in "small" boiler design which have resulted in quite surprising steaming capacity.  Also, most of these would require an external enclosure, a cabinet so to speak, to contain the heat.

These are just a few fer-instances, there are quite a few options.

Thank you, Harry, for your input. I did find the Chattanooga group, but that is too far for me.
I will continue with my efforts with what I have. I have a few irons in the fire that may increase my income in the near future, so I may even be able to buy a kit for a bit bigger boiler...
At least what I currently have to work with might get my smaller oscillators running on steam.


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