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Andrew Johnston23/10/2020 22:12:01
5718 forum posts
659 photos
Posted by John Alexander Stewart on 23/10/2020 18:30:47:
Kozo gives us a way to machine gears good enough for his model Climax, machining on small machines in the average workshop, so I give him top marks.

Quite so and very impressive work. I've recently been sent a copy of his article in Livesteam. The teeth are cut on the slant and the tooth profiles are clearly asymmetric. What interests me is that on some logging locos this is clearly not the case. The tooth profiles are symmetric and the teeth do not lean over. So while the gears by Kozo are a tour de force what really interests me is how were the gears as depicted on the full size engines designed?

The publication I have found starts by stating that the pinion can be a normal straight tooth bevel gear. The key seems to be that for the bevel gear the tooth profile at the outer edge needs to expand, in much the same way as normal and tranverse DP in helical gears.

There has been some discussion of skew bevel gears recently on MEM including some pictures of the gears in production at the Lima Locomotive Works. It's clear that the teeth need to slide as well as roll over each other. Consequently it seems that in real life the gears had poor reliabilty. Apparently after Lima switched to cut gears rather than cast they offered a two year guarantee on the gears.


John Alexander Stewart24/10/2020 11:53:14
779 forum posts
52 photos

Hi Andrew;

Lima Locomotive works made the Shay - straight bevel gears - that is what you see in the MEM thread. Heisler also used straight bevel gears, it's only the Climax that has skew bevel gears. (and, I'm not sure about the Climax class "A" machines - never seen one in person)

Anyway, I'm sure, knowing your skills, you'll find/discover/develop about a half-dozen tooth profiles that'll work!

Andrew Johnston25/10/2020 11:45:02
5718 forum posts
659 photos
Posted by John Alexander Stewart on 24/10/2020 11:53:14:'s only the Climax that has skew bevel gears...........

I never twigged that, thanks for putting me straight! Sadly, as far as I'm aware, there are no full size logging locomotives of any type in the UK.

Looking at pictures of the Climax the tooth profiles all seem to be symmetric whereas the Kozo gears are definitely not. They're straight on one side and curved on the other. In one of the Climax pictures the teeth on the pinion are definitely straight exactly as per a normal bevel pinion. In another the pinion teeth are at a slight angle. Presumably the works made a design change at some point. Looking at the design parameters for skew bevel gears the teeth on the bevel gear are straight when pointing at the shaft intersection. So if the teeth on the pinion are at an angle my working assumption is that the pinion is not located at the theoretical shaft intersection.


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