Advice on upscaling a smaller gauge design?

[kenrinc]

However, I'm sure the boiler will need something more than "supersizing" to make it work properly. Steve Eaton's TOBY seems like it might fit the bill in that department?

I'd appreciate some advice from more experienced hands here. Alternately, does anyone know if there a larger engine that still has the charm of the little kettle?

Cheers,

Chris

I'd second Curtis' recommendation of Kozo books for boiler questions. He's a master in 3.5" gauge and he gives a lot of design information as to the specifics of why it was designed the way it was. His entire design philosophy would work with this style locomotive. I scaled his A3 from 3.5" gauge to 7.5" gauge and, as mentioned, being my first locomotive, it was quite a feat. Yes the vast majority of it is just doubling dimensions but mass has a habit of creeping up on you. Things often do not have to be duplicated or doubled exactly. I found that I did a lot of pre-planning (ie: wasting time) with foam core mockups making sure certain things would work prior to actually purchasing and cutting things. CAD obviously is a great benefit here. I don't see why it wouldn't work.

I like the design and look of this locomotive and wish you luck in the process.

Ken-

[baggo]

Hi Martin,

You should have no problem just doubling the dimensions of the cylinders and the valve gear. That will give you cylinders of 1.5" bore by 2.125" stroke which is pretty standard for 5" gauge locos over here. The port sizes will be ok as well. The boiler will have to be looked at though as you would be increasing the cylinder capacity by a factor of eight but only increasing the grate area by a factor of four. Probably a good idea to have a look at the Sweet Pea boiler for dimensions, number and size of tubes etc.

John

[logotrikes]

Excellent John, much obliged.

Cheers, Martin

[logotrikes]

**Probably a good idea to have a look at the Sweet Pea boiler for dimensions, number and size of tubes etc.**

That was my thinking John. I doubt that increasing the size of the boiler on Toby to suit 5 inch would be as acceptable to a boiler examiner here in Oz as the boiler in Sweet Pea at 5 inch would be. Still the same marine boiler, could be built in copper or steel, and already a proven and accepted design. I'm sure I could make it fit an enlarged Toby. Jack Buckler's book on building Sweet Pea is readily available from TEE Publishing so I'll grab a copy in due course.

You also mentioned grate area as a function of cylinder size, and presumably Sweet Pea's boiler will already be appropriate for enlarged cylinders re Toby.

The AMBSC Code part 2 (steel boilers) has just arrived in the post. I expected a dry dusty treatise, but this book is full of the good stuff, plenty of drawings, weld-preps, boiler samples-stayed and marine. I'm going to enjoy this book...

I've done some preliminary sums with regard to taking Toby out to 5 inch and rather than just double everything, a factor of x1.6 seems appropriate. I'll work on that and see where it takes me.

I'll update my progress, or dismal lack thereof, in due course.

Cheers, Martin