My Big Boiler Build

As mentioned I am constructing a sizable 6"x12" boiler. I have several photographs that I will share, and I will endeavor to present them in chronological order.

The first one I have is shown to emphasize just how much of a struggle I have with my puny machine. But there is always a way to get around limitations like this. I turned wooden discs for each end and was able to chuck tyhe disc with the hole in it and use a centre in the other, not shown here.

Here you can see a similar setup for cutting the ends of the firebox. I used a paring tool so I could get the required travel needed.
Both the outer body and the firebox are both 1/8" thick copper.

Here I am drilling holes for the bushings. Another puny machine, I can't count the number of time I stalled the mill.

Test fitting the outer tube into a brass angle ring, this ring holds the boiler to the base.
Bending the brass angle was a difficult process for me. I posted my concerns in an earlier post and received some ideas for making it a different way. I already had the ring started and being a rather stubborn old coot I persevered for many days and was successful in producing a respectable item.
One thing to mention, the faceplate I made myself a while ago and was rather pleased with it. This was the start of many drilled and or tapped holes, someone once said not to revere the faceplate as a holy object and use it to get the job done.

The outer shell fitted to the brass ring and mouted on the base. I'm planning on firing the boiler with coal or the like and the front of the base is open to accept an ash pan. I have yet to make the pan.

Wow, that's looking promising and an inspiration for me to get up off my backside and back to work on my own. A smaller version, perhaps a third of what you've got showing there; so thanks so much for sharing. I look forward to seeing how your project unfolds. Have you an engine completed or in the works also?

Raygers said:

The outer shell fitted to the brass ring and mouted on the base. I'm planning on firing the boiler with coal or the like and the front of the base is open to accept an ash pan. I have yet to make the pan.


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Very nice! Attached are photos of a very similar boiler I made years ago. It has a 6" Dia. shell by about 7" long with 40 each 1/2" fire tubes up the center.
It has FiberFax between the shell and the redwood lagging. It has a propane burner with a 12V solenoid valve controlled by a pressure sensor. There is a gas pilot light tube that bypasses the solenoid valve. The coil of tubing on the top is for pre-heating feed water. A very good project!

James Brumley said:

Wow, that's looking promising and an inspiration for me to get up off my backside and back to work on my own. A smaller version, perhaps a third of what you've got showing there; so thanks so much for sharing. I look forward to seeing how your project unfolds. Have you an engine completed or in the works also?

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James Brumley said:

Wow, that's looking promising and an inspiration for me to get up off my backside and back to work on my own. A smaller version, perhaps a third of what you've got showing there; so thanks so much for sharing. I look forward to seeing how your project unfolds. Have you an engine completed or in the works also?

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This is my big baby; I started out making a small casting kit and was bitten by the bug. I saw Quinn (Blondiehacks) building this engine and knew that was for me, I love a challenge.

That boiler looks superb!
Well done sir.
K2

Firetubes almost ready for soldering, the four large tubes are for superheaters as per a very involved and lengthy discussion by myself and several experts. See https://www.homemodelenginemachinist.com/threads/optimal-number-of-boiler-tubes.35566/

I used Fusion 360 to model the boiler, this is it in section view. It's only showing two of the 20 tubes to keep the view simple.

I haven't done a lot of silver soldering so it's been bothering me for when I do start soldering the boiler. So to give myself as much advantage as possible I obtained some solder with Cadmium and the black flux.
I tried it out and dispelled most of my fears. Solder flows extremely well compared to solder without. Here's my artwork. I'll sell it to the highest bidder. I can include a banana for extra money, but the price will be very steep.

plipoma said:

Very nice! Attached are photos of a very similar boiler I made years ago. It has a 6" Dia. shell by about 7" long with 40 each 1/2" fire tubes up the center.
It has FiberFax between the shell and the redwood lagging. It has a propane burner with a 12V solenoid valve controlled by a pressure sensor. There is a gas pilot light tube that bypasses the solenoid valve. The coil of tubing on the top is for pre-heating feed water. A very good project!View attachment 164936View attachment 164937View attachment 164938View attachment 164939

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I really like the idea of being able to regulate the burner automatically.

I am sure you are aware, but I seem to recall reading that one should avoid cadmium fumes.
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GreenTwin said:

I am sure you are aware, but I seem to recall reading that one should avoid cadmium fumes.
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Thanks, I've done a lot of reading on the various forums about that. The consensus seems to be that short-term exposure the effects are minimal, if at all.
I've bought myself a carbon filter full mask and plan to do this outdoors when the weather warms up.

Hi Raygers, a suggestion:
If you can bury 3/4 of the tube array in DRY sand, in a bucket/tin, then you will only need half the heat on the top plate when soldering. I have a large coffee tin (2l/4 pints) that serves me well, but maybe you need a bigger one? At least 1 inch of sand beneath and all the way around. Or wrap the job in firebricks: See photos.


These also show the use of "pre-heating" blowlamps, that do not get the silver solder to melt, but mean that when the main Propane torch is introduced to the joint, heat flow away from the joint is reduced making the time for making the solder flow properly is much shorter, and less time for the flux to burn. During pre-heat I use a lower temp flux, then add the higher temp flux when I introduce the Propane torch on the joint proper. After soldering, cover everything so it cools slowly, so differential cooling does not crack any joints! - I have experienced that repairing boilers, where I don't wrap it up, but quickly remove from the sand and air cool... The outside shell cools rapidly, compared to the tubes, and stresses the hotter tube joints, showing any weakness on the subsequent hydraulic test as a leak from a cracked joint! (I have heard a slight "ping!" when I think this happened). - I have made a lot of mistakes, and learned a lot from them.
I like the reinforcement around the Firehole. This is the weakest part of the whole boiler. Huge stress concentration factor at the penetration (3.3 seems to be the accepted Standard SCF). The inner firebox tube is actually in compression: boiler pressure trying to buckle the tube inwards especially at the point where the fire hole reinforcement meets the tube wall. From Thick reinforcement and metal overlap to thin wall of main tube surface needs a silver solder that gives a good fillet (1/8in 3mm), to reduce the SCF at the change of stiffness. - I use 55% silver for fillet making. - Expensive stuff! Also a difficult repair if it cracks and fails, And such a failure is a testament of the "poor design" - not workmanship from the few boilers I have seen. I.E. they are simply operated/tested at too high a pressure. Re-certified for a lower NWP and Safety relief pressure (and Hydraulic test pressure) means they do not fail later, following repair.
My calculations and research of Tech papers at this interface are all indicative of an SCF that is not considered by many designs... so the weak spot can fail a boiler in later life from fatigue, where thin inner firebox wall meets thick fire-hole reinforcement.
The only boiler I inherited to repair and been repaired a few times, due to fatigue from the high stresses - probably from the 2 x Hydraulic test, added to weekly steaming, at a pressure higher than my calculations said was OK. I should be interested in your calculations, if you feel you may want to share them? To learn from someone who has made a boiler like this. Other boilers for which I have produced calculations, to re-certify old boilers (From scratch, where the original design has been lost) have typically come up with a NWP of around 30psi, when the original appears to have been run at 60 or 80 psi, from the old pressure relief valve operation pressure. That would have meant the old operation was on a Safety factor of only 2 or 3, not the "8" of modern Regs. and Standards.

I have also dismantled a Marine/Cornish style boiler with cross tubes on a large firetube and seen where all the cross tube joints had failed, repeatedly, and been repaired repeatedly, when the boiler was operated in a boat at 45psi, or higher as it had been "rated" for 60psi NWP!! It was evident that the wall of the main firetube had deformed as it cracked and failed the joints to the cross tubes. A Design problem for the pressure selected! My calculations said a NWP between 12psi and 18psi would be OK (conservative to optimistic) but a higher NWP (45 to 60psi) would mean the 2 x Hydraulic test would deform the firetube at the stress concentration of the cross-tube joint. Most of the cross-tubes had repairs of Soft lead solder with LARGE fillets on the inside of the Fire-tube - the only area where the joints were accessible.
- I scrapped this firetube with cross-tubes and made a completely new fire-tube assembly. Even so, the new Firetube only has a NWP of 20psi as it is in Compression, with stress concentration factors at the end joints and compressive strength of annealed copper as the basis to the design calculations. (NOT the Tensile strength). Hence my curiosity about your design?
While I think my current boiler analysis is "Safe", it may be too conservative, or risky, so I am open for discussion if you want to privately send me calculations, or design support information on this?
I hope there is something useful in this?
Thanks,
K2

Raygers said:

Firetubes almost ready for soldering, the four large tubes are for superheaters as per a very involved and lengthy discussion by myself and several experts. See https://www.homemodelenginemachinist.com/threads/optimal-number-of-boiler-tubes.35566/




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Looks very good!
I found getting that much copper heated to flow silver solder a real challenge, specially after you install the shell. I placed the assembly on a portable, single burner (electric stove top type) with the bottom portion of the assembly wrapped with a 1" thick blanket of Fibra-fax and left to heat for about an hour. Then applied heat near the center of the assembly with a oxy-acetylene torch with a rose bud tip. Then used a propane torch for spot heating to flow solder around each tube.