Tuesday, October 27, 2009

Chassis with gearbox

For a goods engine you need lots of low down grunt from the motor and gearbox, and not too much top speed. The Bulldog locomotive uses a Markits MM-2L 2-stage box attached to the biggest Mashima motor I could fit in the boiler (don't ask me which, I can never get my head around the number nomenclature).

The 'box comes as usual as a flat etch in surprisingly hard and thick nickel silver. It's cut out and folded up. The end and back plates are soldered in place, I wasn't wild about how well they fitted but solder filled the gaps, then the bearings go in. A quick scrub to remove the flux and the other parts can be fitted.

Of course things are never quite that easy. I wanted to mount the motor at 90 degrees to the lugs and holes provided so a couple of new holes were drilled to allow this before forming. Luckily I allowed a bit of movement as the motor has to be about 1mm above the centre line of the hole provided for the shaft and boss, although this doesn't have to be altered, for the gear mesh to be perfect.

Loads of spacing washers are on the etch yet only two were required to keep the idler gear in position. I fixed the shaft with a drop of superglue and removed the grub screw from the gear so this rotates on the shaft. I find this easier than trying to allow the shaft to turn and then working out how to keep it in position horizontally. Mind you a couple of nickel patches over the ends would have worked in this case as it is very accurately cut to length.

Fitting the box in wasn't too painful either. Despite being pretty bulky, only one frame spacer needed shortening whilst the rounded edges of the gearbox front were squared off to get them in against the back spacer.

The whole thing ran smoothly first time, assisted by the very nice (to my untrained engineering eye) brass gears.

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