The Burrell steering column feels like a big step as it adds another level of detail to this tiny miniature traction engine. First of all though a quick look at all of the parts.
The steering wheel itself was machined from solid brass. Just 22mm in diameter with a 8BA thread in the centre.
The knob was added as a fixed part, making it rotate robustly at this scale just felt too difficult.
The worm and wheel fit snugly. The 20 teeth on the gear wheel were indexed and cut before being hobbed.
They are not perfect, but they are a good pair. It takes 20 rotations of the steering wheel to rotate the gear once. As the drum is 6mm in diameter this means the chains are lengthen or shortened by ~0.95mm per steering wheel rotation.
The bottom end brackets also act as the bearings for the gear wheel and drum. This is a steel shaft acting on thin brass sheet, but the forces are light and the number of rotations over a lifetime will be very low.
It was important at this stage to get the lower column bearing aligned correctly. This then aligned to the steering wheel and gave the correct worm and gear engagement.
The only additional parts are: upper shaft bearing, shaft, shaft boss to steering wheel, shaft boss to worm.
Here you can see all of the parts aligned and fitted to the main tub. The steering column is elevated 38.5° from the horizontal. The lower bearing controls the shaft in both axial directions with locking nuts on the top side of the boss that attaches to the steering axle. The steering axle is 1/16th inch diameter mild steel.
The steering column is just 2.8mm from the axis to the surface of the brass tub. Approximately 2mm of clearance given the diameter of the shaft.
The steering wheel and column to flywheel is also quite tight. The steering wheel rotates smoothly and the drum rotates via the worm and wheel. This will be all improved once all of the bearings are greased.
Finally I had to assemble as much as I have made to show off the Burrell steering column.