Taylor Undertype Engine

Yes I know this is an old design, Greenley from 1908 and the re-design by Taylor from 1971.

Just bought a set of drawings, and there doesn't seem to be any mention of copper thickness, or working pressure, for the boiler.

Greenley suggested 15swg, 0.072", 1.80mm, as suitable for a 5" diameter barrel with 75psi. It is a compound so wouldn't 100psi be better?

With a 5" barrel for a traction engine or loco then 3mm seems to be the minimum thickness?

An alternative could be to make the boiler only 3.1/2' or so diameter, it isn't going to be worked like a loco so just enough steam to turn it over would do. Reduce the copper cost as well!

There also seems to be one or more drawings missing. It is very hard to make out how it is all plumbed together around the cylinders. There is this ring mentioned but what is it for? Why not flange the throat plate forwards and backwards?

15swg does sound a bit thin if the diameter is 5" not to mention an uncommon thickness. As you say 10swg is often used for boilers around that sort of diameter, 16swg is more often found on Minnie and the like which are 2.5"dia.

I'm not sure about the ring you mention but boilers of this era may well have been rivited and caulked rather than silver soldered. A ring is also sometimes used to step up from boiler to smokebox diameter.

100psi or more would stand a chance of getting the compounding to work

This zooms in quite nicely, boiler certainly looks thin, maybe 1/16 when compared to other dimensions and the brass tubes would not be used today

for a 5" (127 mm) diameter boiler at 75 psi (517 kPa) the AMBSC code asks for 2mm thickness (14 swg). They would still be happy with 2mm at 100 psi. 10 swg is obviously OK but why spend more than you need. However with a very old design like this it often pays to compare it with modern design codes, the AMBSC is very easy to follow, designed for model engineers by model engineers.

Bob, I built one from the Taylor drawings a couple of years back, and the ME articles calls for a barrel 5" diameter x 12SWG. I know you are not far away from me, you are welcome to come and have a look. Chris Gunn

Bob I should also say that building the boiler was hard work, I needed 2 torches and had to buy a bigger burner as well. I did use a set of Stuart Turner castings and drawings I manage to get from ebay. I used the ME articles as well, and it all turned out OK. I Think it is a really good looking miniature now finished and painted. Chris Gunn

Just had look at Jasons link to a print on Flickr. The boiler definitely needs updating, but the governor caught my eye - there does not seem to be a return spring, so how does it work?

Martin

12swg sounds a sensible sort of thickness and a nice model Chris

martin I think there is a spring

Martin, there is a spring in the sleeve.

Chris Gunn

Thanks for the response, bit surprised! Never really considered them, couldn't see the point, but saw mine at SRS and looked really interesting.

ME articles? I have just vol 8 from 1903 where I found the use of 15swg but only odds and ends from the 1971 redesign by Taylor which is why I asked about no material thickness or even working pressure from the Sarik drawings. Mind you, they are the size of a bed spread each so hard to use. Sarik haven't yet replied.

If 12swg, 2mm, still seems a bit thin for 5" diameter.

I recently bought a model which dates from 100+ years ago, so the boiler is made as the Greenly design. At the moment just considering it, but 15swg and brass tubes are not acceptable, likewise the riveted boiler. What to do?

Hi Chris, thanks for the offer but looks like I am having to stop driving. What boiler pressure did you run yours at? Did the compounding work as expected? What did you drive, it is a big boiler and just turning it over won't need too much steam!

12swg is 2.65mm

Don't forget that a traction engine boiler is not only a pressure vessel but a chassis as well having to take a few knocks and bumps on the way which yours would not have to worry about. Just a thought.

It only seems thin because it's not what you're expecting. Work out the stress, it's quite modest.

Yes, but we still have the situation where neither the copper thickness or the working pressure is marked on the drawings.

Presumably this is Sarik's pigeon, the drawings need updating.

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Thus cleverly dodging liability for the design ?

there being an implied “for illustrative purposes only, blah, blah, blah”

MichaelG.

The coloured drawing I posted a link to was part of the 1903 Greenly article, clearly has 75psi as the safety valve pressure which would be fair to take as the working pressure.

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… and rather a fine image it is too

I’ve just downloaded the ‘full size’ file to admire.

MichaelG.

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Edit: __ personally, I think the use of “brass tubes” without any material specification might be of more concern than not specifying the copper thickness. …But, It’s from 1903, and ‘of its age’

Note: I have never seen the ‘manufacturing’ drawings, so am only commenting on this image.

Edited By Michael Gilligan on 29/10/2022 10:27:52

I did also mention the brass tubes when I posted the link.

It's not just the main tubes, if the colours are consistant then there is so much brass in there such as the front plate of the firebox, all the firebox stays etc.

I is also almost entirely held together with caulked brass (yellow) screws.

Just like the watercolour washed shading the drawing is of its time just as much as the materials and construction methods. It would be interesting to compare with the later Taylor drawings.

As ever, Jason … you have priority in such matters

I was just demonstrating an interest in a subject that is relatively ‘foreign’ to me.

MichaelG.

Bob, sorry to hear you may have to stop driving that makes life difficult. However the offer still stands if you can get a friend to bring you. I have to confess, I built the boiler to the later Stuart Turner/Taylor drawings, but have not steamed it so far. I piped it up from under the base as well as the boiler, with shut off valve, so I can run it on air for demonstration purposes. That is what i have done, and it runs sweetly on 20psi, so no compounding, but it does seem nicely balanced. I did not drive anything with it, but I do have plans to make a diorama of a machine shop using Stuart and PMR miniature machine tools and line shafting, with the undertype in the boiler house.

Chris Gunn