Hello from Denmark - tips for locomotive building welcome!

Hello!

I'm a new subscriber to Model Engineer after not having found anything quite like it in Denmark where I currently reside.

I am, however, not new to machining. I have set out to build a live steam model of the Prussian P8, also known as BR 38.10. I am fully aware that this is a process that will take years, but I won't shy away.

Anyway, does anybody have any good tips as to where to find ressources for such a project? Google goes a long way for pictures and basic drawings of the profile of the locomotive. But I also need to understand the mechanics of the boiler and so on better.

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

Hi Stradivarius,

Welcome to the forum and may you have many happy hours building your locomotive.

I have absolutely no knowledge of the particular loco but a few comments about scaling full size to miniature might be in order.

Many years ago a prolific writer for ME and other model engineering publications called Curly Lawrence aka LBSC often used to say "You can't scale Nature". What he meant is that if you simply take the original works drawings and decrease the size to the scale you are working to the parts become too weak to do the job.

Similarly boilers need to be designed for the smaller size. A pressure of 100psi in full size might need 20mm thick plates and if you build a one tenth scale model the plates would now be 2mm thick and would be too thin to withstand the 100psi. You would need to lower the pressure by a similar amount to prevent the whole thing blowing up! Also a much lower steam pressure gives a much lower force on the pistons in the smaller size, so it is a double whammy!

You have to over-scale parts to make it viable, so it no longer is a true scale mode, but bears a close resemblance in outline. Of course if you simply want a model to put on display in a glass case that will never be actually steamed then it will work. But we normally spend the effort, time and money to end up with a real working loco to drive.

So although I can offer little real help I hope you have considered these aspects, or you may not have considered them.

Edited By John Fielding on 15/03/2016 14:28:58

Hello Stradivarius

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

Neil

Thanks for the feedback.

@John Fielding

Those are valid points, and definitely something to consider. Half a year ago I was actually welding a small pressure tank tested to a mere 300 psi, and it was pretty much the size of what would fit in a decent size scale model. It was made in 3.6 mm steel, and though the choice of material may not be totally accurate, it will still turn out a very nice model I believe.

Do you happen to know any good books on the structure of steam locomotive boilers and the controls of the steam locomtive?

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

Thanks Jason! Sounds like it could be promising. However, how would I find that issue? The online archive goes back to issue 4153 as far as I can see.

- And sorry for asking these probably stupid questions. I am very new to this website.

I put the article here

Garba-Verlag supply plans for BR38 (P8) & some of the alternative tenders (separately) in 5" gauge.

Live Steam Service supply castings for same. (Download their catalogue to find them).

As you will see both the above have a number of other interesting German prototypes in their catalogues.

I'll be interested to read how you get on with your searches & construction.

Regards,

Phil

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!

If you already make pressure vessels in steel, then I would guess you have the required skills and knowledge of the requirements in terms of safe construction and operation.

If you want to build a steel boiler, you may like to consider a Briggs boiler.

The Australian codes can be ordered from here

Neil

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.

Thanks a lot to everyone. The litterature has been ordered and the drawing of plans will commence soon. Will keep a thread on the forum for the progress of the 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.