02-16-2014, 02:08 PM
It's odd that any shaft would be scored, as they're almost always steel - not likely scored by brass or plastic, anyway. I'm unclear as to the shaft to which you're referring, though, as there can be some confusion in the terminology. A worm gear is the gear driven by the worm, and it may be pressed onto its short shaft or, in some cases, be a loose fit on the shaft and simply rotate on the shaft. The worm shaft on many older locos was an extension of the motor shaft, and while the shaft was invariably steel, the worm itself could be steel, brass, or plastic. Even if there's a separate drive train (plastic u-joints or flexible tubing) between the motor and worm, the worm shaft would be steel.
In a gear set-up where there's only a worm and a worm gear, the worm itself is usually steel and the driven gear brass, or the worm brass and the driven gear plastic or fibre. The thinking behind that is that the softest gear should be the one easiest to replace.
On an idler gearbox, there's an additional gear (or gears) introduced between the worm and the axle gear. This type allows greater reduction (and often a straighter driveline between motor and worm), and the worm and axle gears will be the harder ones, with the idler made of softer material because it's the easiest, by far, to replace.
I'm surprised that 10 minutes of break-in running could generate that much heat, though, and I'm wondering if the drive is all-metal direct from the motor to the plastic gearbox. Is it possible that the motor is overheating, and the heat transfering through the metal parts to the plastic gear casing.
The only other cause which springs to mind is that something was damaged during construction - perhaps a shaft scored when pressing a gear onto it, then the scoring damaging the bearings and/or the gears. Any foreign material in a gearbox will damage anything which is of a softer material.
Any chance you could post a photo of the set-up of the motor/drive assembly?
Wayne
In a gear set-up where there's only a worm and a worm gear, the worm itself is usually steel and the driven gear brass, or the worm brass and the driven gear plastic or fibre. The thinking behind that is that the softest gear should be the one easiest to replace.
On an idler gearbox, there's an additional gear (or gears) introduced between the worm and the axle gear. This type allows greater reduction (and often a straighter driveline between motor and worm), and the worm and axle gears will be the harder ones, with the idler made of softer material because it's the easiest, by far, to replace.
I'm surprised that 10 minutes of break-in running could generate that much heat, though, and I'm wondering if the drive is all-metal direct from the motor to the plastic gearbox. Is it possible that the motor is overheating, and the heat transfering through the metal parts to the plastic gear casing.
The only other cause which springs to mind is that something was damaged during construction - perhaps a shaft scored when pressing a gear onto it, then the scoring damaging the bearings and/or the gears. Any foreign material in a gearbox will damage anything which is of a softer material.
Any chance you could post a photo of the set-up of the motor/drive assembly?
Wayne