Chain skipping

Mark South said:

B. Filing is a very poor way to judge hardness - titanium, for
example, cannot be made much harder (without being ridiculously
brittle) than around 48-50 Rc, but filing it is a pain because it
work-hardens under the file and the soft bits that do go into the
file clog the teeth.

Why is steel that is hardened and very hard, like that used in tools, much
more difficult to file or saw than mild steel (which in turn is more
difficult to file than typical aluminium alloys used on bikes)?

What is so different in principle about the action of a chain on a
sprocket than a that of a file?

~PB

Pete Biggs said:

What is so different in principle about the action of a chain on a
sprocket than a that of a file?

The fact that wear particles will embed in the softer material and cause
wear on the harder (just as white-metal bearings can wear hardened steel
crankshafts). But I don't necessarily think that's what's happening here.

--
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===
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I was sure it meant there was a set of 8yo girlies who were well 'ard!

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"Pete Biggs" <[email hidden]> wrote in message
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Quoted message said:

Mark South said:

A. Case-hardened aluminium can be way harder than mild steel.
B. Filing is a very poor way to judge hardness - titanium, for
example, cannot be made much harder (without being ridiculously
brittle) than around 48-50 Rc, but filing it is a pain because it
work-hardens under the file and the soft bits that do go into the
file clog the teeth. This is what Rockwell gauges are for. C. Actual
hardness does relate very well to wear resistance though.

Thanks for the info. Which make/model chainrings use case-hardened
aluminium?

I'd expect any half-decent industrial aluminium bits to be correctly hardened
for their application. Mild aluminium chainrings probably wouldn't last more
than about 5 miles before the teeth wore off.
--
Mark South
Citizen of the World, Denizen of the Net
<<Tiens! Ce poulet a une grenade!>>

"Pete Biggs" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Mark South said:

B. Filing is a very poor way to judge hardness - titanium, for
example, cannot be made much harder (without being ridiculously
brittle) than around 48-50 Rc, but filing it is a pain because it
work-hardens under the file and the soft bits that do go into the
file clog the teeth.

Why is steel that is hardened and very hard, like that used in tools, much
more difficult to file or saw than mild steel (which in turn is more
difficult to file than typical aluminium alloys used on bikes)?

Well, tools are made of tool steels which are often hardened about as far as
they will go. 64-66 Rc is not uncommon. At that hardness they are very brittle
and do not bend before breaking. Many tools will shatter like glass when
dropped on a workshop floor.

Basically, the harder the material the harder it is to file. (But as I said,
there are softer materials that are also a pain to file.)

It also depends on how hard your files are. You need very good quality files to
make an impression on a well-hardened piece of carbon steel.

For example, I have a knife blade that appears to be hardened to about 61-63 Rc
(not uncommon for decent knives) and some medium quality files that are rated as
62-64 Rc. As you can imagine, it's a hell of a lot of work to get the files to
make any mark at all on the blade and the files wear pretty quickly at the work.

Quoted message said:

What is so different in principle about the action of a chain on a
sprocket than a that of a file?

The pressure load is qualitatively even greater. A file or saw concentrates all
the force onto a tooth or two that then presses impressively hard on the piece
being worked.

A chain is designed to spread the load evenly over a reasonable tooth area, and
over several teeth at a time. The irony is that as the metallurgy improves, the
gains are squandered on using narrower and smaller sprockets and chains....
--
Mark South
Citizen of the World, Denizen of the Net
<<Tiens! Ce poulet a une grenade!>>