On 2013-11-11, John B wrote:
On Sun, 10 Nov 2013 12:25:05 -0800, mike wrote:

Lowes has a sale on Kobalt tools.

They're guaranteed for life, but that's no help if you've
just stripped the head of that #4 Torx screw holding together
the $300 gizmo you're trying to repair.

So, is there any correlation between shiny silver surface and
softness for screwdriver bits? In the store, how do you tell
what's tough and what's not?


As a general statement, steel tools are plated or otherwise coated to
prevent rust so a shiny finish is meaningless. another give away is
that "Cobalt" is spelled with a "C" and not a "K".

Agreed. It is intended to *sound* impressive. :-)

It is, by the way, "A hard, brittle metallic element, found
associated with nickel, silver, lead, copper, and iron ores and
resembling nickel and iron in appearance. It is used chiefly for
magnetic alloys, high-temperature alloys..." and "hard, brittle"
hardly seem appropriate qualities for a tool (except maybe a glass
cutter :-).

Well ... Cobalt alone, no. But the better drill bits (and some
other tools, including lathe bits and parting tool bits) are a HSS alloy
with Cobalt as a component (high Cobalt). The steel looks a little
yellowish -- not as extreme as a TiN coating, but less white than plain
HSS.

When I buy an index of bits I expect to use a lot (e.g. my index
of number sized (wire sized) bits in screw machine length with 135
degree split points is a Cobalt steel.

As an example, go into the MSC site, and look at the
"Metalworking" sales flyer:

http://www.mscdirect.com/FlyerView?contentPath=/sales-catalogs/metalworking

and at the top of page 9 you will find "Hertel Drill Sets", and go down
into the table where it lists "Screw Machine Drills", to the next to the
last -- 60 Cobalt 135 degree split, Wire #1-60 currently on sale for
$99.99. Compare that to the next one up, same size set, but "HSS-Oxide"
which is currently selling for $64.99.

They just call them "Cobalt" -- but in reality, they are a
different HSS alloy which has a higher percentage of Cobalt in the
steel.

Down at the bottom of the same page, they have a summary of why
Cobalt steel is preferred for some things.

And I like the screw-machine length bits, because they are shorter
and have less flex -- as long as I don't need the full depth that a
jobber length bit will give -- and I usually *don't* need it.

Enjoy,
DoN.

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