< Leading & Trailing Wheels >
Before cutting wheel castings, I have to determine the wheel contour. There are two major track standards in Japan. One is OS standard with 119mm back-to-back and the other is Modelnics' 117mm back-to-back. It is difficult to make a loco which can safely pass though both two kinds of turnouts. The drawing shows determined wheel contour. To attain the purpose, the back-to-back is 119mm and the flange was designed as thin as the strength permits, on condition that the castings are made of ductile cast iron.
I started with six wheels for leading and trailing trucks. First, in four-jaw, backside of the wheel was faced off and the center hole (19mm) was opened with drill and boring tool. After that, back recess among the spokes was cut by a roundnose tool.
Here I prepared a wheel cutting jig modifying the jig for William's driving wheel. Once you trued up the jig's outer front face and the spigot, you cannot release the jig until you complete all of operations for the wheels.
In the jig, the wheel was first chucked by screws between the spokes, and then the boss was cut outward from the center with a boring tool.
The screws were replaced with short pins and the wheel was fixed with a disc on the boss. Then the rim surface and step were cut.
So as to finish the wheel contour precisely, I calculated coordinates of the tool tip and moved the tool in 0.1-0.2mm step. After that I removed micro notches by a fine round file.
I found unacceptable blowhole on the tread of a wheel. So I have to cut one more wheel. I have no choice but to release the jig halfway. To minimize the error, I released the jig together with the three-jaw chuck. Then the error was only 0.01mm. Anyway the best method is preparing one more casting from the beginning.
1/20 tapered tread was cut by adjusting the top slider's angle.
They are finished wheels. The left four are for the leading track, while the right two are for the trailing truck. This time I did grinding the wheels with emery cloth, so as to proof against rust.