A simple Stuart 500 style Babcock boiler

[lennart]

Hello,

there hasn’t been any progress on the Chub locomotive for a while. All the upcoming machining would have to be done on the larger machines in the club workshop but I can‘t get there rigth now for obvious reasons.

Back in 2018 I built a simple boiler plant using a commercial Wilesco boiler. It is a simple soft soldered brass pot boiler. It works reasonably good in closed rooms and as long as the steam consumption of the engine that is connected to it is low. But as soon as it gets windy and cold there isn‘t much more than hot water coming out of the steam valve. The picture below shows the boiler powering a small Elmer Verburg oscillating engine.

Babcock boiler plant (1) by Technikfreak L, auf Flickr

To improve this boiler plant I would like to try to build a new boiler by myself to increase the efficiency of the plant and hopefully to learn something about boilermaking. The result of this project might also tell me whether the boiler for the Chub might possibly be within my abilities or not.

This is what I came up with:

Babcock boiler plant (2) by Technikfreak L, auf Flickr

I didn’t bother to include the hand pump and the boiler fittings in the CAD-model since they are already made or commercial items. The chimney (used as a condenser oil trap) is included to make sure that it will fit the boiler and won’t be too much out of scale.
The boiler itself is pretty much a shortened Stuart 500 style babcock boiler with additional bushes on the top for fitting a whistle and a second valve. I intend to fit 3 water tubes under the barrel instead of two and a superheater tube in between. The max. working pressure should be about 4 bar (60 PSI).
It will be my first attempt at making a boiler and at flanging some copper plates. It will not be my first attempt at silver soldering though.

At this early stage of the project, I’d like to discuss some of the design points. The questions about making the parts should be dealt with later. There is a drawing below where some relevant dimensions can be seen.

1_Babcock Kessel Baugruppe V1 by Technikfreak L, auf Flickr

I know that many people here have successfully built even more boilers. So I hope, there are some thoughts on my drawing above and some answers to the questions that arose so far:
1) The 64mm copper barrel is only supplied in 2mm thickness. Should the end caps be made this thick, too? The next smaller size would be 1,5 mm. Does the thickness make a difference in the flanging process?

2) I have read in the ME forum that the inside radius of the flange should be at least as large as the material thickness. So I went for 2mm. I intend to make the flange 7mm deep (measured from the cap‘s inner face).

    Is this deep enough or maybe even deeper than needed?

3) I know that brass is an unsuitable material for the bushes. Several drawings, that I checked suggest to use bronze. Is gunmetal also an option?

I‘ve already said, that most of the design features are taken from the Stuart 500 series boilers. Since I don’t own one, the dimensions which were not given in the data sheets were taken from various pictures.

4) In the Babcock boiler the water tubes are fitted inclined to aid the water circulation. I would guess that the speed of circulation will rise with steeper tubes. I chose an angle of 8° so that the whole boiler assembly

    won’t get too tall. Are 8° enough to ensure proper circulation?

5) If I estimated correctly, the tubes on the Stuart 500 are 5/16” in diameter. The closest metric equivalent would be 8mm. I hope that this isn’t critical, as the next obtainable tube sizes are 6 or 10 mm.
6) Here is the tube layout which I came up with. On the Stuart boiler the tubes are set out like this:

    www.stationroadsteam.com/stuart-500-boiler-without-fittings-stock-code-3230/

    Is there a reason for the tubes not to run parallel? If not, I would just put them in parallel like this:

Babcock boiler plant (3) by Technikfreak L, auf Flickr

7) One thing that I didn’t understand yet is how they fixed the boiler barrel in the housing and therefore how I should do it. Obviously the circular cut out in the cast front and rear plates stops the barrel from being lifted

    up, but what stops it from tilting or rocking back and forth? Maybe the owner of a Stuart 500 can give an answer.

There will be probably many more questions but for now those should be the basic ones.
Maybe there are still things that I’ve overlooked or should change that I didn’t mention above.

[dsa]

Just about to list a 500 on ebay

If you care to send me a PM with e-mail address will photo and send as easier that typingand explaining about the cast in boiler location lugs etc.

Tubes are 5/16  as you said ,  inclined outside two are water tubes and central one is steam  to valve.

David.

[JonL]

I have one of those Stuart boilers but I didn't have the frame so I made one. Worth noting that on the Stuart boiler the bottom/centre tube is a superheater that goes up to one of the outlet bushes.

EDIT: I just read what you put about intentionally modifying yours to be a triple tube! 

[dsa]

Jan 19, 2021 21:52:11 GMT JonL said:

I have one of those Stuart boilers but I didn't have the frame so I made one. Worth noting that on the Stuart boiler the bottom/centre tube is a superheater that goes up to one of the outlet bushes.

EDIT: I just read what you put about intentionally modifying yours to be a triple tube! 

The centre steam tube, which Stuart's intended as a drying tube, as mentioned in my earlier post, is silver soldered to the steam valve bush, which is the fitting nearest the water gauge end. It is the bush with the smallest tapped hole. Can supply bush dimensions and positions if it helps. It runs parallel to the botton of the boiler.

David

Edited to say your  drawing shows this tube in line with the water tubes , but internally it is the full height of the boiler at the valve end and finishes just 0.25 inches short of the top of the boiler at the other end. 

[lennart]

As I have written in my first post, I omitted the superheater tube and replaced it by a third water tube.

I hope that this will be a good choice. The goal is not to produce super hot steam as most of my engines have gunmetal or brass cylinders. The aim is to build a boiler that steams more freely and efficiently than the existing one.

[dsa]

You also say you are fitting a superheater tube ?  I can see you do not need any help from me so I will withdraw from this thread.

Thankyou.

David

[lennart]

After reading through many threads on several forums I came to the conclusion that I better should buy a length of bronze for the bushes and not use the gunmetal that I have laying about.

Hopefully the grade that is obtainable in here in Germany (CuSn8 or PB104 as the equivalent) is suitable for the job.

This should have answered my question no. 3.

Maybe some thoughts on the remaining ones ?

[chris vine]

Yes, you never quite know what is in gunmetal. It might be leaded bronze which might not silver solder very well!
Chris.

[lennart]

There are some news: I got the materials delivered today. 8mm and 64mm copper tubing and some phosphor bronze round bar.

I also made some changes to the boiler design since last week:

1) The flange radius was increased from 2 to 2,5mm

2) The whole boiler was elevated by 5mm to give the fire a little more room.

3) I added two water tubes to give a total of 5. The spacing was therefore made a little tighter. Hopefully this will make an improvement compared to the wider spaced 3 tube layout.

The updated drawing and a CAD-picture:

1_Babcock Kessel Baugruppe V2 by Technikfreak L, auf Flickr

Babcock boiler plant (4) by Technikfreak L, auf Flickr

I have some worries that the spacing might be a little tight now so that the tubes obstruct the flames at getting up to the boiler barrel.

Any thoughts on this? Could the 5 tube layout be an improvement or should i stick to the initial 3 tube layout?

[stevep]

I'm no expert in this field, but I would say that you will be fine with 5 tubes. From the drawing, there is plenty of room for the flames to get past the tubes and warm the main barrel, although I suspect you will get most heating from the tubes, as you will create convection currents in them.

[lennart]

Thank you Steve for your thoughts. So if no unforeseen things happen, I will adopt the 5 tube arrangement.

To make a start on the actual build I made a first try at flanging the end caps. I assumed that it might be easier to use 0,5mm plate instead of the 2mm so a disc was cut from the thin stuff.

I made a former that I also intend to use for the real ones from a 60mm aluminum bar. I turned it down to 57mm but it will probably neede a further reduction in diameter.

So this is the result. Keep in mind that this is the first piece of copper that I ever flanged.

Babcock boiler plant (5) by Lennart Glauche, auf Flickr

The blank was cut to 80mm diameter but was later reduced by about 3mm in radius. It wrinkled a little but after annealing and beating for 7 or 8 times i got it reasonably smooth.

Will it be easier to flange the 2mm plate around the former without wrinkling? The relation of flange depth to plate thickness will be a lot smaller then so I guess it will.

I have read somethere that the former should be 1/64" smaller in diameter than the inner diameter of the flange to allow for some spring-back. Is there some truth about this? Does this also allow for the plate thickness to increase in the flange?

I could figure all this out by myself by trial and error but the copper was too expensive to waste it for those experiments.

[mbrown]

Looks good Lennart.

Other peoples' experience may differ, but I find that thicker plate (within reason) is much easier to flange without wrinkling than the thin stuff.

Regarding the 1/64" allowance, my own approach would be to flange the plate as close to the former as possible, then chuck it in the lathe and lightly turn the periphery to the correct dimension. Obviously that only works for round plates but others can be filed lighty to ensure the flange is parallel and correct to size.

Hope that helps.

Malcolm

[Neale]

Looks pretty good. However, if you are starting with thicker material, you probably have enough to put it in the lathe and take a very light skim over the flange to clean it up, and to adjust the fit in the boiler tube. You are aiming at something like a 0.1mm gap all the way round to allow space for silver solder, not a tight fit.

(I think I was typing at the same time as the previous post!)

[JonL]

Just as an aside (and it's more a musing than anything else), depending on the burner I wonder if raising the height of the outer tubes would place them further into the flame path? At the moment it looks like most of the hot gases will pass over them on their way out.

I have no basis for this other than the look of the thing.

[lennart]

Feb 11, 2021 6:55:38 GMT JonL said:

Just as an aside (and it's more a musing than anything else), depending on the burner I wonder if raising the height of the outer tubes would place them further into the flame path? At the moment it looks like most of the hot gases will pass over them on their way out.

I have no basis for this other than the look of the thing.

That is an interesting point. I thought about this too. I will try to put them in a little higher, but the radius of the bent tubes will set some limits.

I might try to bend the tubes today so we will see, what can be done.

Also thank you to Malcolm and Neale.

I flanged in total 3 plates from the 2mm plate yesterday.

The first one: Each photo was taken just before the next annelaing.

Babcock boiler plant (6) by Technikfreak L, auf Flickr

After 6 annealings and a light clean up on the lathe it looked like this:

Babcock boiler plant (7) by Technikfreak L, auf Flickr

Not too bad, but I still considered it as a failiure.

- There are some deep dents at the 8 o'clock position. They were pressed in by a dent in the plate that I clamped against the copper sheet to keep it from buckling.

- When I tried it in the barrel it jammed, so I tried to push it out with an alluminum bar. It caused the dents and scratches in the center.

- When truing the piece up in the lathe I accidentally hit the radius with the tool post which caused a deep scratch

All this could have been avoided just by being more careful but I was simply not aware how soft annealed copper is.

Nevertheless I learned something from the first one.

The blanks for ther second and third one were cut a little smaller because the first flange was about 3mm deeper than needed.

After the flanging was complete:

Babcock boiler plant (8) by Technikfreak L, auf Flickr

And after the clean up: They came out without dents and scratches.

Babcock boiler plant (9) by Technikfreak L, auf Flickr

So I would call these a success.

The first cap was used again to make a test run on soldreing in the bushes.

I made them to the drawing that I showed on Jan.30 with M6x0,75 threads. The goal was to see if I could solder them in different heat ups without remelting the first one.

55% silver solder was used for both bushes.

The right one was first. I number punched in a 1 and a 2 afterwards but I don't know If you could spot them.

View from the front:

Babcock boiler plant (10) by Technikfreak L, auf Flickr

inside:

Babcock boiler plant (11) by Technikfreak L, auf Flickr

I am quite happy with the solder penetration on the first (right) one, but would the second one have been acceptable?

The next things to do will be the bushes, the barrel and the tubes. Hopefully the bending of the tubes won't cause too much trouble because the radius is pretty tight.

Now the probably most important question, and one of the reasons why I started this thread: The order in which to solder the components together.

I read several threads about the making of locomotive type boilers and the order to solder them.

But as the watertube boiler is very different I am not quite sure.

[lennart]

One point that I haven't thought through is the strength of the end caps.

When I looked at the stuart boilers I couldn't see a stay or any kind of support for the flat areas. Does anybody know, if they fitted a grider stay or something else that can't be seen from the outside?

I guess that I really should support the end caps. The barrel's inner diameter is 60mm so the unsupported area is quite large when I compare this to other boiler designs. Although the working pressure of 60 psi will be much lower than of most locomotive boilers, it still has to survive the hydraulic test.

Since I don't have any suitable material for a rod stay lying about, a grider stay for each end cap may be the better way. I could bend some angle pieces from the left over 2mm copper sheet and rivet and solder those to the end caps.

Will this be sufficient or could I even live without stays at all?

The other major question about the order in which the components should be soldered together is still waiting to be answered.

When thinking about it I came up with several possible ways.

1) Everything in one go with 55% silver solder only. -> Assemble everything with flux, securing the end caps with rivets, placing the boiler vertical with the front (with the four bushes) facing upwards. The tubes and bushes in the barrel are secured with wire. Start soldering the bushes at the front end and eventually flip over to solder the other end cap.

This would only work without the stays.

2a) Solder the end caps and the grider stays with 40% solder which I would have to buy first. Then continue like 1)

2b) Like 2a) but with 55% solder for the grider to end cap connection. I would secure the stays in place with rivets so if the solder remelts later they should at least not fall off.

3a) Solder the end caps as complete sub assemblies with the bushes in the front one with 40% silver solder. Solder them into the barrel with 55% solder. The bushes and watertubes in the barrel are soldred in this heat up too.

3b) Like 3a) but with 55% solder for everything.

4) Like 3a) or 3b) but with the barrel, tubes and bushes in the barrel already soldered with 55% solder. The end cap assemblies are also soldered wit 55% solder. I doubt that I could get the barrel sub assembly hot enough for the higher temp. solder.

5) None of the above

I would really appreciate some instructions, tips, warnings or opinions on this from someone who has more boilermaking experience than I have.

[JonL]

i don't have much boiler making experience (I've repaired a Stuart boiler and I've made a 16mm locomotive boiler which I haven't fired yet) but I can say I saw no evidence of internal stays on my stuart boiler. I actually overpressurised it slightly during home testing as I was using the regulations for a different boiler and the end caps were seen to flex outwards a little. However they stayed tight and haven't given any issues.

[lennart]

Feb 13, 2021 18:34:45 GMT JonL said:

[...] I can say I saw no evidence of internal stays on my stuart boiler. I actually overpressurised it slightly during home testing as I was using the regulations for a different boiler and the end caps were seen to flex outwards a little. [...]

Thank you for the information about the stuart boiler.

Just to be safe I made a quick FEA of the end caps first without any kind of support and with an U-shaped grider stay afterwards. Why not use the student-license for ansys that I got from the university?

Because it is only a student license the accuracy is limited and some simplifications had to be made. So the calculated figures may deviate frome real ones but at least I got somwhere near.

Without stays the flat area of the cap would buckle by about 0,1mm at a pressure of 6bar and would cause stresses of about 90 N/mm^2. Much more than IO would be comfortable with.

If there is some further interest in the FEA, I could post the calculated diagrams here of course.

With a U-shaped grider of about 15x15mm section there was almost no deformation calculated. The arising stresses were mostly below 30 N/mm^2.

I decided to adopt the grider stays and quickly made them out of 2 copper offcuts. They were bent with 2 annealings over an aluminum square bar.

Next I dealt with the 5 tubes. A simple bending device was quickly made out of an large aluminum angle and a turned bending die. It may look very rough (and it was in fact) but it did the job.

Babcock boiler plant (12) by Technikfreak L, auf Flickr

To drill the holes into the barrel it was fixed onto the drill press with this dodgy set up of clamps. I put an 60mm bar into the barrel so that the clamps won't crush it. For most of the work I used a step drill but for some holes with odd diameters a standard twist drill had to be used.

Babcock boiler plant (13) by Technikfreak L, auf Flickr

The tubes were then fitted and adjusted individually. That's why they got numbered. As suggested by nobbysideways the outer tubes were tweaked so that they would go in a little furter.

Babcock boiler plant (14) by Technikfreak L, auf Flickr

Just for the record, I made the bushes out of phosphor bronze. I also turned some blanking plugs for the hydraulic test. I may also fit those before the soldereng to protect the threads in the bushes and to retain the wire that holds them in place.

Now I've got all the bits and pieces together.

Babcock boiler plant (15) by Technikfreak L, auf Flickr

Last thing to do before the solderig is to fit some rivets to secure the end caps.

... still wondering about the best order to solder the pieces together...

[David]

Looking good!

The rings of solder on both bushes look good. You seem to have a complete ring around the one on the left and it's a neater job.

How are the threads in the bushes holding up? All the ones in my boiler got loose after being soldered in :(

I'd put a longitudinal stay in even if I didn't think it was necessary. Just a copper rod silver soldered in holes in the middle of the endcaps. The current brass one with the glass at the end obv doesn't have a stay, but it might be working at a lower pressure than you're hoping for with the new one.

It was mentioned above that the commercial version of the boiler had locating lugs on it to stop it moving fore/aft in the frames. You could silver solder rectangles of copper onto the barrel for them.

As for the order, as long as everything is covered in flux remelting an existing joint should be ok as long as an inaccessible bit doesn't fall off. The endcap girder stays look like the only bits in danger of that and you could secure them with a copper rivet (or a longitudinal stay) to avoid it.

[lennart]

Feb 15, 2021 1:23:27 GMT David said:

Looking good!

The rings of solder on both bushes look good. You seem to have a complete ring around the one on the left and it's a neater job.

How are the threads in the bushes holding up? All the ones in my boiler got loose after being soldered in

I'd put a longitudinal stay in even if I didn't think it was necessary. Just a copper rod silver soldered in holes in the middle of the endcaps. The current brass one with the glass at the end obv doesn't have a stay, but it might be working at a lower pressure than you're hoping for with the new one.

It was mentioned above that the commercial version of the boiler had locating lugs on it to stop it moving fore/aft in the frames. You could silver solder rectangles of copper onto the barrel for them.

As for the order, as long as everything is covered in flux remelting an existing joint should be ok as long as an inaccessible bit doesn't fall off. The endcap girder stays look like the only bits in danger of that and you could secure them with a copper rivet (or a longitudinal stay) to avoid it.

Thank you for your advice.

The two bushes in the test piece came out unharmed. The threads were a little tight before soldering. When they came out of the pickle I checked again and I could not feel much difference.

The current brass boiler was soft soldered and intended for 1,5 bar max. working pressure. They made the rear end cap a little domed to eliminate any chance of bulging.

To secure the new boiler in the base I made a blind bush, that got soldered into the barrel. Just like the ones for fire hole doors on locomotive boilers.

I had some spare time today to make a start on the silver soldering.

The grider stays were dealed with first. Just to make absolutely sure that they would not come off later, I used 40% solder and fixed each of the stays with two rivets.

It did not result in the neatest joints, but it will do the job.

I then soldered the water tubes into the barrel. To make sure that they will stay in place I tied two pieces of wire around them. I also soldered the blind bush in the same heat up.

55% solder was used for all the joints in this stage.

Rings of solder placed onto the tubes:

Babcock boiler plant (17) by Technikfreak L, auf Flickr

I applied another coat of flux over the rings after taking the photo.

Just after the heat-up:

Babcock boiler plant (18) by Technikfreak L, auf Flickr

And after the three sub-assemblies came out of the pickle bath:

Babcock boiler plant (19) by Technikfreak L, auf Flickr

I am quite happy with the water tube joints, although one joint has to be revisited when I solder the bushes. (The lower one of the foremost tube, the solder didn't run through all the way around)