< Driving and Coupled wheels >
Driving and coupled wheels are made of cast iron. Before turning, the castings are cleaned (removed sand and burr) and painted.
In this setting you can cut the balance weight without disturbing the bosses.
Same as the pony wheels, I prepared a special faceplate with a spigot to machine tread and flange of the wheels. Once you chuck and true up the jig, never release it until you finish all of the turning operation.
Normally the holes for crankpins are bored in a bench drill with a positioning jig, and reamed by hand. But I bored and reamed the holes in the lathe. Note the jig which I used for wheel turning is used again to ensure positioning.
The crankpins are glued to the wheels with Loctite #603. I added lock-pins to the driving crankpins so as to prevent the crankpins from turning.
The axles are also glued to the wheels. This "quartering" is done in the lathe. The left side crankpin is hold horizontally on a suitable length of round bar, while the right side crankpin is hold vertically along a square gauge. Don't forget to insert axleboxes and eccentrics to the axles before the quartering.
Pony truck spring plungers and housings are provided as integrated castings. Don't saw the two parts off at first. You can chuck one end in the three jaws when cutting another end.
I added a simple side-control function to the pony trucks. Along a round stretcher, two sleeves with coil springs push the hook of the pony truck from both sides. Side-control force is adjusted around 1/3 of the pony axle weight.
Axlebox is supported by coil springs. This typical manner has, I think, two disadvantages. The axle weight doesn't push but pulls the pins. It means the thread in the axlebox has to resist the axle weight. Additionally, the pins are close to the rails and easily damaged once the loco derails. In the case of "Rob Roy", in which the coil springs are located onto the axleboxes, you are free from such problems in exchange for adjustability.
Coil springs are coiled from stainless steel drawn wire, around a mandrel chucked in the three jaws. To obtain desired size of coil springs,
1) Diameter of the mandrel should be 10% smaller than the desired inner diameter of the coil.
2) Number of turning should be 10% more than the desired number.
3) "Pitch" of coiling should be 10% shorter than the desired pitch.
You have to use "piano-wire cutter" to cut the drawn wire. If you use a general cutter here, it will be spoiled immediately.
The erected chassis on a club layout.