Supporting > Boilers

My first Boiler build

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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.


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.

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?


--- Quote from: chucketn on September 23, 2018, 03:49:37 PM ---Are there any hard/fast rules or formulas for making the formers?
--- End quote ---
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.
--- End quote ---
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?
--- End quote ---
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.

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.


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