Hi all!

I'm an absolute beginner to model engineering, but have been interested in the subject (and miniature locomotives in particular) since I was a small child. I grew up in the Westcountry, so there was plenty of inspiration to be sought (Dobwalls, Gorse Blossom…so it goes on).

A friend convinced me to attend the Sandown show 18 months ago (and I returned last year), and the seeds have been truly sown. I was offered a Colchester Student roundhead at a price I couldn't refuse a few months ago…and I now need to use it to build something!

After much soul-searching, I have pretty much settled on building a quarry Hunslet in 7.25" gauge. The rationale was based on a number of factors. Firstly, I want to work in 7.25" so that a future standard-gauge locomotive would be a sufficiently large artefact as to be aesthetically pleasing to me. I'd go larger still if I thought it was remotely sensible! I admire the amazing work that goes into the smaller gauges, but even 5" is too small for me – see earlier comments about Dobwalls, etc! Secondly, I fancied the idea of starting in narrow gauge, as the physical size dictates that everything is less fiddly. The Hunslet appealed to me, as it's compact, for narrow gauge, simple (just four wheels, etc)…and last but not least, I've always fancied owning one!

I've found Peter Beevers' website (http://www.beevers.org.uk/min_rly/holywar.htm) to be particularly helpful so far, including sanity checks. I have a pretty good idea of what it's going to cost, and how long it's going to take.

I'm aware that there are several options for building a Hunslet in 7.25 – including the Milner (approx 4&rdquo, Ross Harrison "Lilla" (3.5&rdquo, and Alan Ruston "Elidir" (3&rdquo designs, both from looking at suppliers, and the "general introduction" page of Peter's site. In a nutshell, the first hurdle is that I'm struggling to work out which version is the most appropriate for me. Do forgive me if I state the obvious at any point here – I'm trying to get it all straight in my head, as much as anything! I suppose a book on Hunslets would be a worthwhile investment…!

Back-story complete, down to the first question (of, I suspect, a great many)! The weight data quoted from various sources doesn't quite seem to add up, to me.

I've answered the other question I had by myself in the process of researching for this post, which was that the prototype of Lilla, on which the Harrison design was based, was a larger design than the majority of (Alice-class) Hunslets. Mystery of how the 3.5" scale version could be bigger than the 4" version: solved!

Anyway, down to weights…

The Milner (4" scale) design is quoted as being between 48" and 52.5" long, and weighing somewhere between 250-300kg.
The Ruston "Elidir" (3” scale) design is quoted as being 35" long, and weighing around 125kg.
As a curve-ball, the Maxitrak 5" gauge version (2" scale) is quoted as being 25" long, weighing just 30kg.

I know the weight relationship is non-linear, but can the Ruston design really be half the weight of the Milner? Taking it even further, can the Maxitrak design really be just around a tenth of the weight of the Milner design?! That doesn't 'feel' right to me!

Weight is a significant factory for me, as I am hoping to transport the finished product in the back of a (large) estate car (without cab…I prefer Hunslets without them!). Does anyone have confirmed dry and wet weights for the Milner and Ruston versions?

My gut feeling is that I prefer the Milner-sized version to the Ruston one. I suspect it would be wise for me to track down an MES where members have one of each, and go and have a good look.

I'm sure there will be more questions down the line! Apologies for the extended essay, but I thought it would be useful to start with a little context!

cheers

James

Thanks for your replies, folks!

Thanks for the sanity check, pgk. I should probably have done some maths before opening my mouth…! Those figures (especially for the 4" scale variant) give some serious food for thought.

Julian – I have heard references to people up-scaling the Don Young design to 7.25". If I were to look at doing that, I presume I could use some of the castings from the natively 7.25" designs, in principle, subject to suitable research?

I'm beginning to get the impression that none of this is remotely simple, and the scale of the task is beginning to dawn…!

Is this passage length issue an inherent design feature – does it affect the prototypes, too? What effect does it have? I presume it's a result of the steam chests being inside the frames (as illustrated below, from a CAD drawing for the Don Young design)?

If I have understood the expansion link discrepancy correctly, the issue at hand is that loco links require larger throw eccentrics – potentially too large to fit in a model. The launch link will inevitably multiply the throw of the eccentrics, but the geometry of the whole arrangement must be adjusted to correct the changes this will make to the valve timing. Am I along the right lines there?

Moving onto the suspension offset point; I fear this has gone over my head. I've found a reference to what you're talking about on Don Ashton's website, but I'm not much clearer. To clarify, suspension, in this context, refers to the method of vertical location of the expansion link (to set direction of travel / cut-off), correct? Most are centrally suspended, but some are "end-suspended" (i.e. the link to the reverser is attached at one end of the expansion link, rather than in the centre of its travel), which is taken to be bad on account of influencing the relative effect that the two eccentric rods will have, right? Offset of the suspension point refers to an offset between the centreline of the pivots for the suspension point, and the valve rod, correct?

Assuming I have the concept at hand correct, what does the offset achieve, or is that a question best answered by experimenting with a valvegear simulator?

I guess the key point here is that it's worth checking it all using a simulator, right?

Wow, this is a serious learning curve…! Thanks all for your input – it's very helpful.

cheers

James

Many thanks, Julian!

When you say the valves are driven from the front of the steam chest on the Don Young design, I'm picturing something involving rocker arms…? The site I borrowed the picture from last time lead me up the garden path (or, rather, I only skim-read) – the boiler is borrowed from the Don Young design, but the rest is scaled up from the prototypes – http://ww3.tiki.ne.jp/~hwata/e-Hunslet_201011.htm – hence the long passages and launch links

Is it fair to say that Don's design includes various improvements over the original design, so is not an exact miniature replica? I presume that this all scales more or less linearly (boilers aside!), so the originals would perform better with the design adjustments?

I had better take a look at the Don Young drawings, I think! And then check everything with simulation.

I am gradually leaning towards a 3" design, but I'd like to try to see both in the flesh, preferably back to back. I'll get in touch with my local MESs!

cheers

James