Making a boiler without a lathe

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James Powell
Posts: 318
Joined: Fri Oct 28, 2011 10:42 pm

Re: Making a boiler without a lathe

Post by James Powell » Tue Oct 09, 2018 10:34 pm

10 Wheeler Rob wrote:
Tue Oct 09, 2018 5:56 am
The boiler should not be made from brass, use copper or bronze. The zinc in brass dissolves into the water over time and it becomes porous and weakens. Brass works for piping, tubing and external fittings, that can be easily replaced if they age out.
The answer is "it depends". We've tossed a whole boiler after 2 years due to excessive corrosion. So, it may be possible to use brass fittings _IF_ the owner is willing to scrap it after a year or possibly 2. I've also had brass fittings from Stuart Turner go zipping past my nose off a 504 boiler. (the safety valve, strangely enough, and no, I wasn't busy clouting it with a hammer at the time...).

The boiler we scrapped was electric fired, made from some 5" copper tube (or I think it was 5", it might have been 4" ), with steel end plates with O rings. The element was a 1500w electric element from a small hot water tank. The 1/2" plate ends had severe electrolysis corrosion after about 1 1/2 years, to the point of being unsafe for further use. (more than 1/2 way pitted in isolated locations). We figure there were a lot of impressed currents in the boiler in relation to normal boiler designs, because of it being electrically fired and with more copper than steel. (both are not good for boilers).

The good news is that it was just the end plates that were scrap, and the shell was OK, with fittings getting stripped off. I think the 504 mentioned ^ was the direct replacement, which was a step backwards as it required either gas or large quantities of alcohol to fire. (I got the short end, and had to use Alcohol, as dad had the propane @ his house).

Good places to start with for any boiler design are doing the math involved. Model Boilers & Boilermaking (KN Harris) would be my go to book for figuring strengths. If it is a commercial design, someone _should_ have done said calculations, but it is always reassuring to do them for yourself. (also puts that school learning to use !). A boiler that won't steam your model is a disappointment. A boiler that isn't strong enough is a bomb. (the 970 BTU/LB of latent heat is a LOT of potential energy).

James

k4kfh
Posts: 23
Joined: Sat Oct 06, 2018 10:08 pm

Re: Making a boiler without a lathe

Post by k4kfh » Wed Oct 10, 2018 10:19 am

Okay, thanks. I am trying to put together a budget for this project and the fittings are by far the bulk of the cost, as expected. I'm curious, for fairly low pressure (30psi) steam, do I really need a pigtail syphon for the pressure gauge? I can save about $10 in compression fittings and tubing if I can just thread the gauge directly into the boiler.

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NP317
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Location: Northern Oregon

Re: Making a boiler without a lathe

Post by NP317 » Wed Oct 10, 2018 10:27 am

Yes, you still need a siphon for the pressure gauge.
The steam temperature can damage the delicate bourdon tube inside the gauge.
~RN

k4kfh
Posts: 23
Joined: Sat Oct 06, 2018 10:08 pm

Re: Making a boiler without a lathe

Post by k4kfh » Tue Oct 16, 2018 3:51 pm

I'm thinking of taking the Popular Mechanics design and turning it vertical, with the coil fittings threaded into the end cap. This will make it easier to fire with a simple propane backpacking stove, which I already have. Does anyone see any issues with this idea?
NP317 wrote:
Wed Oct 10, 2018 10:27 am
Yes, you still need a siphon for the pressure gauge.
The steam temperature can damage the delicate bourdon tube inside the gauge.
~RN
Assuming I go through with the vertical idea above, would it be sufficient to simply mount the gauge below the water line on the boiler (towards the bottom)? I'm asking because I'm trying to save cash on fittings, and I already have a bottom-mount gauge around, so it would be dirt cheap and easy to just use a 90" NPT fitting threaded straight into the boiler. As long as I kept the water above the gauge fitting, is there any reason this won't work?

Kimball McGinley
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Location: Laguna Niguel CA

Re: Making a boiler without a lathe

Post by Kimball McGinley » Tue Oct 16, 2018 7:06 pm

The 90 elbow idea in the water space will ruin the gauge.

The idea behind the siphon is that it fills up with condensation and still transfers the boiler pressure to the gauge, but not the heat.

It probably also helps that it places the gauge some distance away from the shell too, both in tube length and proximity, which also reduces heat transfer.

k4kfh
Posts: 23
Joined: Sat Oct 06, 2018 10:08 pm

Re: Making a boiler without a lathe

Post by k4kfh » Wed Oct 17, 2018 10:16 pm

Kimball McGinley wrote:
Tue Oct 16, 2018 7:06 pm
The 90 elbow idea in the water space will ruin the gauge.

The idea behind the siphon is that it fills up with condensation and still transfers the boiler pressure to the gauge, but not the heat.

It probably also helps that it places the gauge some distance away from the shell too, both in tube length and proximity, which also reduces heat transfer.
Ah, that makes sense. I'll just do a proper siphon then. Thank you for the information.

k4kfh
Posts: 23
Joined: Sat Oct 06, 2018 10:08 pm

Re: Making a boiler without a lathe

Post by k4kfh » Mon Dec 03, 2018 7:19 pm

Well I did it, mostly. I'm not too happy with the hacked-together base, so I may rework that into something more like the traditional sheet metal enclosure eventually, but a friend had this scrap laying around so it works for now. I've got a small leak around the water glass bottom fitting that I've got to straighten out, but it steams the little engine nicely, and tested the whole thing to double working pressure (about 90lbs) with no problems.

For anyone who is wondering, I fire it with a little Chinese backpacking stove which can be run on a propane/butane mix, or with pure propane using an adapter. I did this because a propane torch does a terrible job of spreading the heat across the coil, and because a little campstove like that can be had for under $20, unlike the similarly sized ceramic burners which would cost upwards of $90. Plus this comes with the right jet, hose, and gas valve; no assembly required!

Thanks for the advice everyone!

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FKreider
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Joined: Fri Feb 02, 2018 8:44 pm
Location: Sturbridge, MA

Re: Making a boiler without a lathe

Post by FKreider » Mon Dec 03, 2018 9:27 pm

k4kfh wrote:
Mon Dec 03, 2018 7:19 pm
I may rework that into something more like the traditional sheet metal enclosure eventually
Post pictures when you re-work the base, with a proper firebox and the engine and boiler mounted next to each other on a single base this would be a nice looking little set-up.
-Frank K.

rkcarguy
Posts: 905
Joined: Tue Aug 22, 2017 10:33 am
Location: Wa State

Re: Making a boiler without a lathe

Post by rkcarguy » Tue Dec 04, 2018 12:03 pm

James Powell wrote:
Tue Oct 09, 2018 10:34 pm
with steel end plates with O rings
Sounds like you've got a battery there, with copper, steel, and the O-rings to "isolate".
Those two are far apart on the galvanic corrosion chart.

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