Although most of it is doubled up that can result in quite a chunky looking engine as the 1″ was quite thick in places. For example the horn plates would come out at 1/8″ when 3/32″ or more likely 2.5mm thick material will look a lot better.

As for wheels if I were making another 2″ engine I would go with rolled rings and welded in “washers” to form the legs of the tee section. Again the doubled up thinknedsswill look excessive, 3mm would do (2.5mm spokes) rather than just over 5mm that the doubled size would give. Others have sourced thick wall steel tube and made the rims from that.

Go upto 10g for the barrel if copper were used and 3mm plate. As for the tubes you probably won’t end up with the best steaming engine by keeping the same number, it would be better to fit more smaller tubes into the space, you could easily go upto 20 tubes. You will also need more stays as doubling the spacing is not ideal, rather than the 3 x 3 pattern something like 5 x 5 would do with 9 of those hollow for fixing the hornplates, the others from 1/8″ copper rivits. Probably wants a couple more full length stays too.

As for a steel boiler which will need to be welded by a certified welder although it could be done again it may not be the best steaming engine. As a rough guide at that size the boiler barrel and plates would need to be double the scaled thickness to allow for wasting (rust) so you are looking at 6mm thick. This will reduce the water volume and also the grate area neither of which help with firing. If steel were used it would be best to go with expanded in copper tubes as they don’t need to have a wastage allowance and you could get a reasonable number in, maybe it would come down to 16.

I would also think about moving the pump away from the boiler and you would really need to add an injector as a second means of filling the boiler.

Before buying or cutting any metal for the boiler talk with whoever will be inspecting, testing and certifying it to ensure you are making a design they will pass

On 7 February 2026 at 12:37 Bazyle Said:

Is the Minnie, when at 2″ a sufficiently simplified design to make it a good choice wrt the many other 2″ designs that are better supported?

Depends what you want from it. If you want a quick build and somthing solid to get you out onto the rally field then a reasonable choice (subject to boiler alterations) Cheap as you really only need the cylinder and flywheel castings.

If you are more into the building and want a scale looking engine then there are better choices. Something like the MJ Engineering Fowler A7 is far more detailed and true to prototype so many more happy hours in the shed and as a bonus they run well too. Lots of castings so more costly but as the build will take longer your outlay per hour is similar

There are 2″ scale Minnie builders out there finished and unfinished perhaps a call for them to contact you would be helpful.