I think that a good approach would be to look at what the advertisers in Model Engineer have to offer such as plans and materials. You will also have to decide which scale you intend to build to. There are several standardised track gauges but these do not always reflect the scale. For instance, I build Gauge 1 locos which run on a 45mm track but Garden Gauge locos also run on 45mm track but are of a completely different scale. The scale that you are able to build to will also to a large extent be governed by the sort of equipment that you have or intend to acquire. These are just a few pointers for you to consider and hopefully someone more experienced than I will be able to take you further. Meanwhile, good luck.

Mick

Hello Stradivarius

Welcome to the forum. Others have modelled the P8, a while spent on google should turn up some useful information.

Neil

Looks like there was a photo of a model in Vol 168 No 3919 "3 1/2""g. German class P8 by M.Verhellen"

I put the article here

Hi Stradivaius,

The use of steel for boilers is a sticky subject!

First off what is the grade of steel?

Secondly, what is the yield point at, say 250C, which it will have to withstand in use.

Just those two factors have a huge bearing on the safety of pressure vessels. The fact that a compressed air tank needs Xmm of wall thickness will become most likely 3Xmm for steam at the same pressure because of the high operating temperature and the continuous cycling between cold and hot. So yes there are very good books on the design of steel boilers and the subject is well documented for full size boilers. But as far as I am aware no such design rules exist for model size boilers. Remember the statement "You can't scale Nature".

I think before you get too involved you need to speak to a knowledgeable boilersmith and explain what you would like to do. He may think it is possible but then again he may warn you off.

Another factor to consider is corrosion. In a full size boiler with a wall of, say, 20mm plate a little corrosion pitting of 2mm depth isn't of much concern. But in a small boiler it will corrode and pit to a similar depth. So if the wall is, say 4mm then the pit is now 50% of the depth and is a serious concern.

Copper on the other hand is pretty elastic under high temperatures and has much better heat transfer than steel. Hence, why it is the traditional choice for modellers, although the material cost is much higher. By being more elastic it can safely expand a bit to withstand the pressure and it doesn't work harden to the same extent as some grades of steel. Boiler plate or tube is not your average MS sheet or pipe, it is very special and costly, so the difference between it and copper is not much different.

Sorry to throw cold water on your plans but you need to unedrstand these parameters, it could save your life!

Suggestions for books relating to model boilermaking;

"A Manual of Steam Locomotive Construction" by Martin Evan

"Model Boilers and Boilermaking" by KN Harris

Both these books are quite elderly but should be available new or used.

All the best with your project.

2mm is plenty thick enough to contain 100psi, and at that you would have a 5 fold safety net. Its even higher in steel but you have to add extra 'meat' to allow for rusting. Model boilers are massively over engineered, thing is its the joints which are likely to fail long before the shell does. I have the industry standard excel spreadsheet which came from a very well known commercial boiler house, you can have a copy if you pm me? The books quoted are so out of date in terms of modern materials and technologies that they are of, in my opinion, very limited relevance. I now only build steel boilers for my locos.