On Fri, 2 Aug 2013 15:49:25 +0000 (UTC), David Lesher
wrote:

Side topic:

I have read that the Wehrmacht's tanks, esp. the later ones that
were so large, suffered badly from final drive failures. So much
so that a road march of them for any distance would disable
say 33%. This helped me better understand Allied anti-railroad
tactics...forcing them onto the roads.

[They also lacked tank retrievers of enough strength to
salvage them....]

The failures were because of 2 basic reasons: they lacked
sufficient chromium to fully harden the gearing, and the second
was my question.....

This source (that I now can't find again...) said there was a
way to better design/machine the ring gears needed, but Germany
lacked the tooling/resources to use that approach, and instead
used less strong methods. I inferred the better way needed more
time or a better mill but beyond that, I don't know.

I'm curious about what that might have meant, and wonder if anyone
can speak to gear design issues...

Only in fragments. If the issue was an internal-tooth ring gear, as
for a planetary gearset, that wasn't a milling issue. That was a
gear-shaper issue. They also can be broached, but I don't see that as
likely during the war, on big gears. Perhaps that's the tooling that
Germany lacked. It requires very big pieces of high-quality tool
steel, and chromium shortages would be an issue.

Germany had some very good gearmaking capability but that of the US
was better at that time. Gleason was the world leader in making big,
strong gears of several types.

BTW, the US had power-transmission issues on some tanks at the time,
too. Caterpillar made a big 24-cylinder porcupine diesel engine that
was supposed to be the end-all for our largest tanks. But it had so
much torque that it twisted off driveshafts like they were swizzle
sticks.

--
Ed Huntress