Given that this is the first locomotive I've built where I've had to form the entire chassis and gearbox I'm really happy to see all the wheels turning move under their own power. The test did highlight a slight issue with the way I'd put the gearbox together though.
If you look at the gear on the rear axle you will notice that on the lower surface it has a boss that extends out along the axle which isn't present on the top surface (you can just about see this in the photo to the left, but it is a lot clearer in the photos from the previous post. The problem is that when the gearbox is fitted the larger part of the gearwheel is fouled by the boss if it is fitted on that side of the axle gear.
Fortunately it is easy to fix this by simple rotating the gear in the gearbox (given I can't swap the wheels around as they are permanently trapped in the chassis). Although the worm and gear are now no longer in line they still mesh nicely and everything turns freely.
I would be sorely tempted to strip the gearbox and swap that gear around again, to keep the first gear and worm aligned. Then, with a fresh blade in the scalpel, carve away the boss on the axle mounted gear and slide it back along to where it was before. Otherwise you risk wearing away one side of the first gear wheel with the worm.
ReplyDeleteI did think about doing that, but so far I haven't for two reasons. Firstly I didn't want to risk damaging the gear on the axle as it will be impossible to replace, but secondly looking at the instructions I think that even with the original parts the alignment of the worm and large gear wasn't meant to be straight.
DeleteWhen I did have the gear in the gearbox the other way around, but before fitting the worm, the wheels would rotate and turn the gearbox when manually pushed along the track. There was no obvious clearance between the small wheel and the boss and the wheels were stiffer than before but they did turn. Adding the worm gear and power though and the whole thing locked solid. Part of that was I'm sure the boss, but I think it might also have been that the worm was pressed two tight against the gear. Moving the gear sideways gives me a good mesh that turns freely.
Looking at the instructions for the old parts I think the small gear was also inline with the motor shaft and the worm and gear where meshing off centre, so maybe this is the intended design given the motor mounting.
I think I'll leave it as is for now but keep an eye on the gear for wear. If it does show any obvious signs then I should be able to replace it and swap it around without too many issues.
I'd agree with Paul Mark. I have never been involved with plastic gears. I have built several limited slip diffs and mesh laterally and vertically is critical on pinion gears. Worm wheels may be different. They are good for low power transmission. The famous Hewland racing gearbox was a VW Beetle box casting used upside down. It was a wonderfully accurate casting but I knew a bloke that had a skeleton box to mesh crown wheels and pinions in, then he line bored the castings to suit. Folk were putting up to 185bhp through a gear box casting that was designed for 25bhp. I never reached those dizzy heights I got just 145bhp at the wheels.
ReplyDelete.
Okay I've now had a play at changing things around, but I've reverted everything to as described above. Turns out that with the motor mount being where it is there isn't enough room for the gear to be inline with the worm, regardless of the boss on the axle mounted gear. Also having asked about this on one of the railway modelling forums, it turns out that I've built it as it was designed to be built even with the change of parts. The offset gear takes up less space and this approach is used in many of the Backwoods Miniatures kits. Also the suggestion is that the brass worm will actually wear quicker than the plastic gear so I should be fine.
ReplyDeleteFair enough then. Seems to be an odd way of doing things but if it works (and the video clip proves that it does)...
DeleteLooking forward to seeing more progress.
Looks marvellous with those lovely little wheels turning. I would probably go with the "if it works, leave it alone" school, and as you say, it can be sorted if you spot any undue wear. I am so impressed with how the model looks under the footplate. Obviously, the upperworks are wonderful too, but there's a real complex feeling to the etches under the boiler. I'm looking forward to more, too!
ReplyDeleteYes, I do love the way it looks under the footplate. I may be a bit of a snob but I really don't like a lot of the models that use simple looking motion etc. or hide the wheels behind tram skirts just so they can use simpler power units (the kato tram chassis for example). It does make building the model more complex of course but I think it's well worth it.
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