Cheating On The Corners (mini-blog)

It was Francis James Cartazzi, an engineer with the Great Northern Railway, who had a jackpot idea. It is called a Cartazzi axle; and please don’t ask fbb how it works. In very simple terms, it allows the fixed axle to be a bit less fixed and move from side to side and thus cope with the curves of the track.

fbb can find no photos on-line of this genius engineer.

But a normal OO model loco would simply not be able to go round the corners if the back axle section were solid.  “Toy” model railway corners were very sharp!

The solution was easy peasy, make it a pony truck anyway; no one will notice.

See the two wheel “bogie” dangle. So standard was this modelling procedure that fbb always thought that the real 12-inches-to-the-foot A4 actually had a pony truck at the rear!

How ignorant can you get?

But modern collectors of expensive  locomotive models would not tolerate such a bodge. The frame needs to be solid all the way. So on Hornby’s model of the LNER “Hush Hush” W1 4-6-4 class loco, the rear 4 wheels  are part of a solid frame.

So, how does it go round corners?

Horny cheats in a different way. Although the boxed model is equipped with prototypical flanged wheels, on many models those rear four wheels do not have any flanges. You can see the effect below …

The driving wheels have flanges but the back “4” do not; so they are not constrained by the rails. On sharp curves and viewed from directly above, those wheels would hang out over the rail.

Thus, if you want to use your loco on tight model curves, you buy a set of flangeless wheels as below.

But there’s more complexity to this problem. Here is a model of a British Railways standard class 9F 2-10-0.

And the centre driving wheels have no flanges. This helps the model go round the corners. But it’s no cheat because here is the centre driving wheel of ….

… the full size 2-10-0 92220 Evening Star, the very last steam loco built by British Railways.

And it has no flanges; which helps it go round the corners!