At what point is a boiler big enough to be steel instead of copper?

[Berkman]

Wasn't one the NKP berk models built with a superheated copper boiler from the UK? Wonder if they run it at 100psi, I think I'd much rather have a steel w/ copper flu boiler that can run at 145psi... would give a much greater margin of error when firing it.

[tsph6500]

You need to set your OP based on the weight on the drivers and the throttle design or else the locomotive will spin the drivers at the slightest touch and be not much fun.

Look at the whole system.

I have a Berkshire that I ran for a while at 140 psi and an Atlantic that is set to 80 psi. Each has about 20 psi above what is the optimal pressure to run at. So the 4-4-2 runs best at 60 - 70 psi.

Keep your safeties at 5 to 10 psi below pop-off by managing your water level. They need only lift once a day. I learned that running full-size engines.

[mattmason]

I run it hard.

Yes sir, you do.

P7084899.jpg

Thanks for the picture, John. I remember that run and replay it in my head often. Taking the train from the Berkshire and walking away with the Chiggen Little was awesome. I asked to use the train and was told, sure, if you can pull it. Barry didn't really think I'd pull away with it. When I pulled out of the station, many jaws dropped in disbelief.

I was a little surprised going up the 1.1% with that train (heavier than I thought), but still got 95% up without help. I think I broke some hearts that day that you don't need a big loco to pull a lot. I did burn off the 2500 degree paint on the smokebox that trip. Graphite paste went on next.

I only run at 100psi. I can weld, but silver solder is a little foreign to me. It works fine, but up to the person making the boiler to which material to use.

[10 Wheeler Rob]

Above 5 inch diameter it becomes cost prohibitive to build a copper boiler. Below 5 inches it is very difficult to build water legs around the fire box and have very fire grate area left.. Neither copper or steel boilers will fare well if you let the crow sheet get dry.

[Bill Shields]

I have a 3/4" Hudson with a 5" steel boiler. ..and I have seen 1.5" scale locos with 8" diameter copper boilers....generally built in the UK as mentioned earlier.
Bassett-Lowe is one company well known for copper boiler production.

Choice of materials is generally a factor of cost and allowance for corrosion...not strength of materials at time of construction. Very few scale locos need in excess of 100 psi to operate. In many States there are regulations which come into effect if over 100 psi...no matter what the size of the boiler.

i have personally been inside of a full size loco boiler in the UK that has a copper firebox 2" thick married to a steel outer shell.

My current project has a 5" copper boiler that has roughly $1000 worth of copper and silver solder invested.

Would I ever build another small boiler from steel?...no...but if you do not have copper available nor someone who can build it...steel is a semi-viable alternative provided you take care of it.

[Joe Tanski]

I have built 4 larger boilers all out of copper,two 1 1/2”4-6-0 8”dia to 7” tapered ,all out of flat copper sheet rolled,a 1 1/2 4-4-2 english Atlantic
(Rebuild 1937 Pandora )8” flat rolled sheet,and a 1” nyc 4-6-4 Hudson all flat sheet copper, was a lot of fun to build,all silver soldered ,all run great
At 100psi ,all were hydro tested to 200 psi. Why did I build them out of copper well I was able to buy three 4’ Sq sheets of new copper at a great price
In a scrap yard .only thing I can say is the build went easy ,but you have to use a lot of acid cleaning between forming and anealing of PCs .if you follow
The design and method wisdom that our English brothers have published over the years Copper boilers can be built at home with high quality results ,and the best part is NO RUST DOWN THE ROAD
JOE

[super7b]

I have built steel and copper boilers for both 5" and 7 1/4".
Both had their pros and cons and both types were successful in the respective locos. I did all the work on the copper ones and all the work on the steel except the welding which was done by coded welders.
Current 7 1/4" loco boiler is tig welded copper. 8" dia and too heavy to lift, so used a commercial firm here in the UK. 3 month delivery and reasonable price.

steamtechnology.co.uk

If you are interested in looking, just a satisfied customer.

[mattmason]

I run it hard.

Yes sir, you do.

P7084899.jpg

Not always.

[shild]

Thanks for the replies everyone!. I would guess copper is for me since mine will be a small to medium 3/4" loco. Flanging the boiler tube plate is probably one of the most difficult things to do building the boiler isn't it? Is it possible to buy pre-flanged plates?

[Builder01]

Flanging a copper tube sheet is actually not difficult. I found it the most fun part of building my copper boiler. Silver soldering is much more difficult to do well. Here's the link to my website showing the steps to flange a copper plate into a fully formed tube sheet.
https://supersimplex.yolasite.com/Flanging-a-Plate.php/

[Bill Shields]

Heat and beat . Repeat

Basic blacksmithery

The throat sheet is the most challenging

Yes you can purchase boiler pieces. Try Reeves in the UK for an idea of how it is done.

[NP317]

If you do not have any of the Kozo Hiraoka books on construction of his 3-1/2" gauge steam locomotives, get one. Or several!
https://secure.villagepress.com/store/i ... /group/124
They contain excellent instructions on making copper boilers, forms for flanging plates, and silver brazing techniques.
Priceless books.
RussN