First Boiler info

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Senior Citizen
Dec 17, 2009
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Near Jonesborough, TN
As my interest in model steam engines grows, the thought of a boiler to run them is nagging me. I have never seen, owned, or operated a model scale boiler. This thread will be used to ask questions and gather resources for a first boiler build.
I am reading everything I can find on model boilers, from 100+ year old books to more recent writings like Stan Bray's book(ordered but not received yet). I have found a lot of reading material online.
If you have built, and operated your own model boiler, I ask you to post at least the name/style of boiler, where you got the plans, and where you got the materials. I'm in Tennessee, USA, so especially looking for resources near me, but all are encouraged to post. Recommendations on simple, home built, favorite designs are welcome.
I am also looking for plans and information on safety valves, pressure testing pumps, gauges, burners, and any other accessories needed.
I prefer a design I can build, but if there is an affordable kit available, info on that would be nice. By affordable, I mean I'm on a limited OAP budget...
Hi Chuck
I'll be watching this thread with interest. I can't offer any experience of my own, but do intend to build. I do think that making a safe, efficient boiler is half of the project of making steam engine, an aspect that seems less popular with the model hobbyists. There is classic little book by Westbury on flash steam which (in my limited knowledge) seems to offer a good summary of flash steam approaches for (boat) models, circa 1970.
For a first boiler I would go for a proven design and there should be a couple on this site by Sandy Cambell
Model Boiler making by KN Harris although a little old is still a good guide and is available online
Building Small Gas Fired Boiler by Alex Wiess has a bit more upto date info as in stay and fire tube calcs that use the correct formula for fire tubes
Find a copy of the new UK model engineering boiler code as it gives some insight for testing and construction and to what a tester will be looking for
This simple build by a very good friend and a very knowlegable builder may give a wee bit of insight
You may glean some more ideas from this
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I have purchased and read Stan Bray's book, "Making Simple Steam Engines". In fact, I've read it cover to cover, at least 3 times. I have a lot of Doctor appointments for my wife and myself, and I take it along to re-read while sitting in the waiting room.
Today I decided to start drawing up and making some boiler bushings, and safety valves. I haven't been able to find any copper pipe larger than 1 1/2 " locally, or any bronze for the bushings and valves.
In Bray's book, he recommends bronze for bushings, but states brass can be used if necessary. I have brass, so that's what I'll use.
I just finished reading the thread here on soldering boilers, and it sparked a question. If silver solder won't fill gaps, how do you get a good fit between the arch of the copper pipe for the boiler and a round bushing shaped like a top hat? Won't the flange of the bushing have more than .05" gap at the point farthest from the center of the hole on the sloping side of the pipe?
Chuck. Are you suggesting that you are contemplating a gap of 50 thous? If so, I doubt that you will be able to fill it.
I seem to recall a necessary 'wicking' of silver solder if you are say doing a boiler tube into a boiler or a fitting into a boiler. Might I 'humbly' suggest that you practice on dummy bits of say copper sheet, bore a slightly slack hole for the tube/fitting, flux up, put a tiny ring of silver solder to the ring, melt the wet flux so that it all sticks and then blow it up with your torch until it melts- which should be a neat fillet of solder. Then, and this is what we taught professionally, to cut it in half and examine what you did- or didn't do.

Again, follow my earlier but unacknowledged advice to limit the solder ring with a soft pencil and perhaps use a dab of solder paste and then flux up etc, etc.

If you are considering doing the 'dip the silver solder rod, hot into the flux and expecting it to work, forget it- for the time being. I CAN do it but I've had a lot of experience. Again, might I suggest that if you make too big a hole( it has happened!!!!!), swage the tube a bit to make the wicking possible.

Meantime, best of wishes for your health as well as your efforts.

bush flange gap.png
I've drawn a 'sketch' in Fusion to better illustrate my question. The circle represents 2" copper pipe for the boiler body. The blue L bits are the sectional view of a bushing. The red area is of concern. The bush is 5/16" dia where it fits the hole in the boiler. The flange part is 5/8" wide and 1/8" thick, and produces the gap in the red circle. I used Fusion's inspect to determine that gap is .038" wide at the widest part.
Can I reasonably expect silver solder to fill that gap?
I have silver soldered some things before, never a copper boiler and bronze/brass bushes. In fact, I taught electronics soldering in the USAF for several years. I know these 2 operations are quite different, but there are also some similarities. Both require clean material surfaces.
And Norman, I have used the lead pencil ring, and the old fashioned typist correction fluid to keep solder contained.
I'm a practical guy and no nothing about playing with CAD or whatever.
As a simple sort of character, I'd 'tin' the mating parts of the boiler and the attachments with silver solder.
We called it 'sweating' but what the USAF and the US Embassy Flight lot called it is anyone's guess. If you have a tinned surface and fit the two parts together, I would suggest that you give it a dirty big bonk with with a hammer and reduce the daft space of what you illustrate as a CAD drawing. Your new fitting should allow proper wicking between the two parts. With that in place -and daft CAD thrown out of the window, you can 'flux up' the joint and run the silver solder as I described earlier.
Perhaps you will 'dummy run' and either agree- or disagree on a piece of scrap.
Silver solder will form a fillet around the bush but if the hole the bush fits into was 50 thou over it would just pour through it
Form the solder into rings to fit around the bush it saves waving the rod around like a one handed fan dancer and makes for a neater job
I have formed an indent for bushes in the past but its not really needed or at least thats my experiance
Lead free bronze would be a better choice for bushes as brass can /will dezinc and crumble after a few years as I found out the hard way
I can do you a few pics if needed of a 2 inch boiler Iv recently made for a small steam loco Elly The Steam Tram
Cheers just my two bobs worth
As I use Fusion to draw up what I'm talking about, it showed me if I decrease the diameter of the flange of the bush, the problem I'm talking about diminishes.
I am aware of the 'de-zincification problem', but this boiler would not see a lot of use. A few firings when completed, and then just an occasional firing to 'show off'.
Chuck I think there is some confusion here , the "gap" is where the bush enters the boiler tube and this can be as close as you like , i.e a 1/2" dia bush goes in a 1/2" dia hole . The gap between the flange and the tube doesn't count , and it will fill quite easily with solder.
The secret to silver soldering is getting the temperature in the right place , if the joint area is cooler than the surround the solder won't go where it is needed , take the time to bring the thicker bush up to temperature before adding the solder.
Aside , some years ago JMathey and Co advertised a 1" ground steel bar forced into a 1" reamed hole and silver soldered. The test piece was then sliced in half lengthwise to show the amount of solder penetration which was suprisingly deep. This demo showed that the clearance required for the solder is minimal.
I would just like to add that your drawing shows a flange that is much larger than necessary. a 5/8'' flange on a fitting in a 2'' boiler really exaggerates the problem. The pic shows a typical fitting as purchased from miniature steam.


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    boiler fitting.jpg
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As my interest in model steam engines grows, the thought of a boiler to run them is nagging me. I have never seen, owned, or operated a model scale boiler. This thread will be used to ask questions and gather resources for a first boiler build.
--------------------------------I'm in Tennessee, USA, so especially looking for resources near me, but all are encouraged to post. R-------------------------------.
Watching this one too! I am also in TN, Dandridge, not all that far from you. I have a Stewart Twin Launch kit inherited from my dad, he barely started it before he died. Little machining has been done to it. It is decades old, did not include the reversing gear, but I purchased the drawings from Stuart and will make it reversable.
I am also retired now, Was a machinist/Tool and Die maker for about 15 years, followed by decades of being a machine design engineer, and now have a nice lathe and Bridgeport to work with.
I just retired a couple weeks ago, and one of the things on my list is building the Stewart engine, and would love to steam power it eventually.
Hi, boilers can be dangerous things & I would recommend [as others have] you go with a proven design. Further, you should build your boiler to a proven set of specs. Here in Oz. we have an association called AALS [Aust. ass. of Live Steamers] which put out boiler codes. In fact, if a boiler doesnt meet these specs the boiler cant be used in public; but I wouldnt like to be around a non spec boiler anyway. I'm sure there would be a similar sort of code in the US.
With regard to S solder gap. A fillet 'weld 'at a join wont be very strong. The fill needs to contact both surfaces as much as possible. It is common here to use a thin iron wire spacer to seperate the join. The easiest source for this is the plastic coated 'ties' which hold together bags & cables etc. ?You may have them there. Pull off the plastic & you have the correct gap. They can be left in while soldering & cut off afterwards.
Be safe & the best of luck with your build.
Hi Chuck,
Further to my last post, which I had to finish early due to other commitments:-
A 2" copper boiler wont be large enough to run an engine the size of the Stuart except for a few seconds or revs. Look at the cross sectional size of a 2"pipe & imagine it 2/3rds filled with water. The remaining area holds the steam. Its not very big.
A few revs is all you'd get from that volume, & that size boiler wouldnt be nearly big enough to replace it.
I had a similar engine several years ago & built a 6"vertical fire tube boiler for it which comfortably produced the volume required under load.
I purchased my plans from E J Winter [in Oz]
They have plans for a "5"& 6" Boiler which would suit your needs.
Ensure you purchase seamless copper pipe. This is quite a large & expensive undertaking, & a challenging, but not impossible, first boiler project.
I am sure you will receive help from the forum if required.
Best of luck.
I'd envisaged a tubed boiler, hence my references to melting in tubes with rings of silver solder.
Oddly, I have two rings of silver solder which are 3" in diameter. They were 'rescued' from the closing down of a local Royal Ordnance factory. I suppose that something like 25pounder shells were silver soldered.

Even more oddly, I still have sets of orthodontic pliers , some of which were designed to shape nickel chrome wire as well as silver solder into neat rings.
on silver soldering -
I used to build bicycle frames, old school - brazing chrome moly tube into lugs.
Silver 'soldering' is more like brazing than (electronics etc) soldering (tin/lead) - which I've also done plenty of.
We should refer to silver soldering as silver brazing. If you approach the question of flux and fluxing as if it is tin/lead style soldering, you will very likely be unsuccessful. Flux removes surface corrosion from the metal. Silver solder will only bond where the flux has cleaned the metal. The flux cleans the metal when it is molten. You can't rely on it to flow.
Per my brazing experience, I make a water paste of dry flux and paint in on all (already cleaned) surfaces to be brazed, then assemble, and remove excess flux. I then apply heat. Silver will flow where the metal is up to temperature and where the flux is. But not where it isn't - which is an easy way to make a clean job :)
In my opinion you are spot on, although S.S, will tend to flow towards the heat source, & I have known it to push the flux ahead of it [if its significantly overfluxed] & spoil the job a bit; as has been mentioned a pencil or correction fluid line can prevent that.
A 6"copper boiler will dissipate a lot of heat & will need at least two torches [I use Mapp cylinders] therefor a two man job, unless of course you can hold the rod in your mouth & direct it accurately. [Only joking-the picture I conjured up in my simple mind amused me].
Good luck to all.