Author Topic: My first Boiler build  (Read 1379 times)

Offline chucketn

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My first Boiler build
« on: September 17, 2018, 06:11:09 PM »
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.

Offline MJM460

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Re: My first Boiler build
« Reply #1 on: September 19, 2018, 01:51:10 AM »
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.

MJM460
The more I learn, the more I find that I still have to learn!

Offline chucketn

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Re: My first Boiler build
« Reply #2 on: September 19, 2018, 01:04:59 PM »
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...

Offline GWRdriver

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Re: My first Boiler build
« Reply #3 on: September 20, 2018, 07:29:57 PM »
Chuck,
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 40mm± 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.
Cheers,
Harry

Offline chucketn

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Re: My first Boiler build
« Reply #4 on: September 20, 2018, 11:50:12 PM »
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.

Offline MJM460

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Re: My first Boiler build
« Reply #5 on: September 21, 2018, 06:15:28 AM »
Hi chucketn, well with no club nearby you are on your own, but then a club only provides some assurance of knowledgable oversight, you still have to take responsibility for what you do, just in days before inspections and codes.  There is no substitute for common sense and no protection from stupidity, as has often been said. 

Providing the tube is seamless drawn tube, as Harry says, it will hold enough pressure, it is the  detail you select for the ends that determines the strength of your boiler.  Make it any length that suits you, that is not important for strength (unless you have flue tubes).

I would suggest starting really simple, with a plain pot boiler consisting of your tube for the cylindrical shell, ends from copper sheet of similar thickness, but flanged as described in most books on simple boiler construction, and bronze (not brass) bushes for a fill plug, the steam outlet and a safety valve.  The joints should all be silver soldered.  Look into clearances for the joints, silver is at best an expensive filler, if your gaps are too big, but at the same time, needs a little clearance to run into for best strength.  Many small commercial boilers remove the safety valve for the fill point.

Think about how to support the boiler and a casing to direct the flame appropriately, with suitable allowance for expansion as it gets hot.  Designs which have a longitudinal stay through the centre are easier to support.

If you are just wanting to run your small oscillating engines, unloaded or lightly loaded, some sort of Meths burner will be adequate.  I have attached a photo of the first boiler I made, which is of the same size tube that you described, and it is more than adequate to drive the engine shown which is 12 mm bore and 16 mm stroke, double acting.  Does not even have water tubes under.  If you include those as well, it is still not very complex, but will steam better.    I fill the burner with 30 ml of Meths (about one ounce) and it heats up in about six minutes and runs for about 15, which tends to be enough to make it a real steam engine.  If you want longer runs, you might need a bigger water capacity, or you will also have to address the issue of maintaining an adequate water level.  I would not go for flue tubes in a small horizontal boiler as a first effort to give maximum water capacity in your size of tube.  You can go for fancy in a future project.

Even a Meths burner can be tricky, so simplest of the lot for firing, is a simple metal tray holding some of those solid fuel blocks sold for portable hiking stoves.  It will take a better spirit burner than any I have been able to make to melt your silver soldered joints.   I would strongly suggest you not to go for soft soldering.  And really recommended to make your fuel supply small enough to run out before the water.

And I would reiterate my suggestion that you make that feed pump first so you are equipped to do a pressure test when you are finished.   Like most of us, you will be anxious to try it our when complete, and it becomes a temptation to not wait while you build the pump.  It does not have to be big, as you do the test with the boiler full of water after displacing as much of the air as possible, so it only takes a few pump strokes to get it up to pressure.

I find my little engines run quite well enough on only 5 to 10 psi, so you do not need a high pressure.

Will be interested to see how you go.  Nothing like running your engines on real steam.

MJM460
The more I learn, the more I find that I still have to learn!

Offline chucketn

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Re: My first Boiler build
« Reply #6 on: September 21, 2018, 11:56:58 AM »
Thanks, MJM460, for the encouragement.
Yes, a very simple pot boiler for the first one, and running simple oscillators to start.
I plan to make the ends from the same tube as the body, but flattened out and formed with flanges.
I have a friend that is a retired tool and die guy. I'm taking the safety valve I made to him today to help me test it.

Offline chucketn

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Re: My first Boiler build
« Reply #7 on: September 23, 2018, 03:49:37 PM »
I’m ready to make the end plate formers for my small horizontal pot boiler. The body tube is 1.625” od,  and 1.512” id, thus a wall thickness of .056”. I have both aluminum, and oak available for the formers. Are there any hard/fast rules or formulas for making the formers? With either material, I plan to have a center hole for a mandrel to turn them on. I’m leaning toward turning the former out of aluminum, as I have enough copper tube for a couple more.
I’m also making the end plates from pieces of the tube, so the end plates will be .056” thick. What would be the minimum radius for the flange? How wide should the flange be?
I’m following Stan Bray’s design Boiler # 1, in chapter 14 of the book “Making Simple Model Steam Engines”, but I couldn’t find 2” or 50mm tube. I assume the former diameter would be tube id – (wall thickness x2) and the blank disk should be a diameter of tube id + (flange width x2), with some allowance for the radius of the flange bend.
Last question, which is the best orientation for the end plate in the body tube, flange pointing in or out? Why?

Offline GWRdriver

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Re: My first Boiler build
« Reply #8 on: September 23, 2018, 10:00:39 PM »
Are there any hard/fast rules or formulas for making the formers?
Chuck,
Everyone is going to have a slightly different approach, but there are a number of guidelines for good practice.

In this particular case I would use Oak for your former, . . the hardest kiln-dried you can find.  I draw flanges tight to my forms and aluminiumumum tends to want to hold on to copper and won't let go.  Steel and hardwood are better about that.  If you have it handy I'd turn the form from a block of wood so that you have an extended base to chuck up and/or hold in a vise while forming.

Usually three annealing heats to "dull cherry red" (and three beatings) is sufficient to turn flanges to full closure, which should be an easy job in .056" copper, but even so the copper will let you know when it needs to be re-annealed.  It's not good practice to overheat it, or force it to bend further when it begins to harden.

Generally I hold a 1x thickness inside radius on heads, and for your project a 1/4" flange width (on the flat) would be sufficient.  I also use no more fasteners (rivets, screws) than necessary to hold everything securely in place during soldering process.  If you want to use rivets for aesthetics that's fine, but the silver solder is what creates the structural strength.

Quote
I assume the former diameter would be tube id – (wall thickness x2) and the blank disk should be a diameter of tube id + (flange width x2), with some allowance for the radius of the flange bend.
That's correct, but I usually add a few thou' to the flange OD for a machining allowance and then I skim my flanges to provide a solder gap of .003-005".  Then I add center deep punch pips at several places (3-4) to maintain the gap clearance and hold the head in place while soldering.

Quote
Which is the best orientation for the end plate in the body tube, flange pointing in or out? Why?
For your application, where I'll assume the heads will be visible, I would place the shoulders out, flange in, and let the shoulders protrude a bit so that the head stands 1x thickness or a bit more proud of the tube end.  That's an aesthetic touch, and the way full size boilers were made.  You could do it either way, but shoulders out will make the most presentable job.  Another reason, depending upon your fittings arrangement, might be that having flanges out might cause a foul between a fitting and the flange, or at best having to fiddle with fittings "in a hole."  Shoulders Out also puts the head and flange in tension rather than compression, but at these pressures and temperatures that's inconsequential.

A couple of other things . . . you'll need a "backer plate" of some kind to press against the face of the blank as you begin to form the flange, otherwise you'll get roll, or "pucker" around the edge as the copper tries to resist being rolled over.  Oak is fine for this, and a disk is the most efficient shape.

I've attached a photo showing how I skim and trim a finished head.  The head is mounted on a "base" chunk, pressed against the base with any sort of backer, and then use light cuts. 

I'm sure we all have our own list of practices which will produce good results.  Those (and a few more) are mine.
« Last Edit: September 23, 2018, 10:30:17 PM by GWRdriver »
Cheers,
Harry

Offline chucketn

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Re: My first Boiler build
« Reply #9 on: September 24, 2018, 12:32:35 PM »
Thanks for the comments, Harry. I have a piece of 5/4 oak that I will make the former from. I'm going to use a hole saw to cut several circles of oak and glue the stack together.

Offline MJM460

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Re: My first Boiler build
« Reply #10 on: September 24, 2018, 12:47:48 PM »
Hi chucketn, you asked about the inside radius of the curvature between the flanges and the flat ends.  The codes I have seen specify a minimum of one times plate thickness, but bigger is better if it does not interfere with any bushes for fittings, like a level gauge in the ends.  However, for a boiler with no provision for making up water for continuous running, a level gauge is an unnecessary complication.

Similarly a flange overlap of three thicknesses is acceptable of the flange is visible for inspection - I believe this means on the inside, so you can check for full penetration of the solder, otherwise four thicknesses.  So probably sensible to aim for four.

You can face the flanges in or out, but facing in is slightly stronger for internal pressure, at least for dished ends.  For a flat end with longitudinal stays there is probably less difference.

MJM460

The more I learn, the more I find that I still have to learn!