The Frames

This is the foundation of the locomotive and there are a number of decisions that need to be made before starting on this component.

Materials
The plans call for either 1/8" or 3/16" steel plate which of course will affect other dimensions on the locomotive. I chose to use 4mm plate because it's the nearest metric equivalent to the thicker size. It's a matter of personal preference and you will find this a recurring theme in this wiki.

Be aware that the actual thickness of sheet metal can vary considerably from the nominal size. For example 4mm sheet was measured at 3.885mm. This needs to be taken into account when making the buffer beams and the pump stay, both of which attach to the internal face. The external dimension over the outside of the frames is the reference size as this determines the gauge of the locomotive.

The plate needs to be flat and even be bought laser cut if you choose. I have no information as to how accurate these are but it's probably fair to say that they wll need checking against the drawings and hand finishing. Presumably they don't have any holes machined in them so there's a lot of work still to do. See below...

What profile?
The plans come with an alternative frame outline that is intended to more closely represent the full size locomotive. The plans show that the pump stay needs to be raised if the alternative profile is used, and the hole in it for the pump needs to be lower as a result. I won't be fitting the water pump, so the hole will be omitted on mine.

Presumably the laser cut frames follow the original design.

Errors
As drawn, there is very little room to fit the front brake hangers and blocks because they are so close to the cylinder head nuts. (See picture) It is possible, but it may be worth considering the option mentioned below.

There is also an issue with the clearance between the crosshead and the piston rod steam gland which is perilously close. This issue doesn't occur if the valve gear is made to either of the two alternative geometries that will be described elsewhere.

One solution is to extend the whole front section of the model to give the desired clearance and that's what I've elected to do. I've added 1/8" to move the cylinders, buffers and smokebox forward. The length of the smokebox is now 1/8" longer to accommodate that. The length of the crosshead guide bars increases by 1/8" too of course.

If you don't intend to fit the brakes or you're happy to design new ones for the front then this isn't necesary.

Construction
The traditional way to produce these is to bolt the two frame blanks back to back and cut them together. This is the way that most builders still go about the job, even if they're using CNC machines. The plans don't show most of the holes on the frames, the inference being that these will be added as necessary.

I chose to add many of these at this stage but it's up to the individual builder as to when you add them. Bear in mind that if the holes are required on both frames, you may want to bolt the frames back to back again to make sure that they are in the same place.

One tip is to ream two or more of the holes at the extreme ends of the frames so that dowels can locate the frames accurately at a later date. The buffer beam holes are ideal candidates for these.

Valve gear
The position of the hole for the lifting arm is decided by what valve gear you choose to fit. Another page will be dedicated to this.

Cylinder blocks
A considerable amount of heat is transmitted from the cylinder casting to the frames. It may be worth considering adding a thin gasket of Steam Jointing paper between the cylinder castings and the frame to reduce this. It will be necessary to compensate for this thickness somewhere, perhaps by removing the same amount from the cylinder face. Any heat in the frames can potentially end up warming up the water in the side tanks.

Axle Driven feed pump
If it's decided not to fit this pump, the stay can be move towards the rear of the locomotive so that the screws miss the wheels. This gives the option of using hexagon headed screws instead of countersunk types.