Material for traction engine gears

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Material for traction engine gears

This topic has 7 replies, 5 voices, and was last updated 15 September 2022 at 11:57 by SillyOldDuffer.

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13 September 2022 at 20:15 #613434
Andy Stopford
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@andystopford50521
I'm building the 1" Minnie and am going to make the gears myself.

The book suggests buying steel gears, but I was wondering whether cast iron would be easier on my Cheapo Chinese gear cutter set. I haven't tried them yet, but I've heard they tend to wear quite quickly (the cutters that is). I don't want to use brass (or plastic!) on appearance grounds.

Has anyone any thoughts on this?
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13 September 2022 at 20:15 #30249
Andy Stopford
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@andystopford50521
13 September 2022 at 20:41 #613436
Anonymous
On my engines the crankshaft gears are steel, EN8:

The 2nd shaft gears, final drive pinions, and final drive gears are cast iron:

The bevel gears in the differentials are also cast iron:

Cast iron would be prototypical. I am building relatively large engines where tooth loads on the crankshaft gears tend to need medium carbon steels, but I suspect cast iron was used in full size.

I have used cheap gear cutters for experiments, but I'd be wary about using them for real gears. The ones I have never seemed to run true. I doubt that cutting a small number of gears, steel or cast iron, will blunt them.

Andrew
13 September 2022 at 20:51 #613438
JasonB
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@jasonb
I bought some very cheap chinese ones and would say they wore quicker than the reasonably priced ones from China via RDG.

Still got a few gears out of them and at a few quid each could be considered disposable.

You would probably still want to do the crankshaft gears in steel so the cluster can be soldered together but CI will be OK for the larger ones. My Fowler has a mix of steel on teh smaller ones and the final drive is a casting. Superba that I have castings for has mostly iron gears.

These were cut from steel with the very cheap cutters
13 September 2022 at 21:22 #613440
Andy Stopford
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@andystopford50521
Thanks chaps, steel for the crankshaft gears and CI for the others sounds like a plan. The ones Jason shows look like a pretty decent result from the cheap cutters – I'll watch out for them not running true
14 September 2022 at 23:06 #613568
bernard towers
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@bernardtowers37738
What's the matter with silver soldering cast iron?
15 September 2022 at 06:56 #613585
JasonB
Moderator
@jasonb
Some people find it more difficult though I have done it myself and with the small bores involved on the Minnie removing the carbon after you have driven it to the surface by heating could be a bit fiddly.

As Andrew said tooth loads on the crankshaft gears will be higher too though not many tend to try and get a Minnie to pull them along
15 September 2022 at 11:57 #613631
SillyOldDuffer
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@sillyoldduffer
Posted by bernard towers on 14/09/2022 23:06:43:

What's the matter with silver soldering cast iron?

Carbon (as Graphite).

Cast Iron isn't a single alloy, it's a family. Some of them contain much more free Carbon than others, and Silver Solder can't bond to Carbon. So you get chaps who find cast-iron is easy to silver-solder and chaps who find it very difficult: they're both right – it depends on the type of cast-iron they are working with.

I noted Jason's comment with interest: 'removing the carbon after you have driven it to the surface by heating could be a bit fiddly'. Exposing more Iron by heat with an oxidizing flame sounds a good idea because flux has no effect on Carbon. Strong heat needed I think: though Iron acts as a catalyst and drops the ignition temperature of Graphite from over 740°C, the flame still needs to heat the surface to over 600°C.

Dave
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