Torque arm for 622

I puzzled until my puzzler was sore about how to affix a torque arm to the NWSL 28:1 gearbox. #10 taught me that we want the arm to be as beefy as possible. But these little 4-4-0s don’t allow us to be profligate with space. In particular, there is no extra space on top of the motor; there is space on the side because it’s a flat can, but the gear box bulges inconveniently on the side.

In the end, I fashioned an L-shaped bracket that screws to the front of the gearbox. It has a small 45-degree angle in the corner to provide room for the motor contacts and wires. The contacts sticking down from the end of the motor are quite inconvenient, and wouldn’t fit at all in the boiler barrel.

Following Don Ball’s suggestion, I ran the motor while the the silicone set. For some reason, even with that good advice, it is slightly happier with a small shim to hold the motor 1/2 mm away from the gearbox.

3 thoughts on “Torque arm for 622

  1. Hi René,
    Generally speaking, motors need to have a (very) small amount of end-play to accommodate the loads in reaction to the worm drive. Ideally you will put a series of very thin brass washers between the motor and the gearbox, using shim. As many as you can fit in: say 4 x .005”. There will then be an ability to absorb the shocks/load but with an absolute minimum of end play.
    Hope that helps.

    1. Thanks Simon. The gearbox includes bearings that pick up the thrust from the worm. Would you still recommend .020” of washers? I don’t think they will do anything.

      1. If the gearbox has thrust bearings inside, then no additional ones are required! The half millimetre gap is probably just breathing space!

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