Thanks Ned, but I can't help but see some holes in your remarks.

I was trying to steer away from the modulus characteristics because they
aren't relevent, but you're right, that all steels fall within a small
range, I forgot while I was thinking too hard about flexibility.

HSS can be annealed, but then it doesn't cut steel. The shank of a HSS drill
or reamer can be filed, but it's not a grade/level of hardness that would
make a good cutting tool for metalworking.
Full hard HSS cuts most steels very well, annealed does not.

Full hard HSS doesn't flex, it snaps.

Several times when I referred to a saw blade bending, I was talking about
traveling around bandsaw wheels, bending (and then straightening)
repeatedly.

I find it real dificult to read that you would suggest that it doesn't
matter if the tooth gullets in a saw blade were cracked. Yer yankin a chain,
but it's not mine. Good Grief.
With cracked gullets, I wouldn't expect anything less than a fairly sudden
blade failure, especially on a commercial horizontal bandsaw.

There are saw blades where all the teeth are interrupted, they're
carbide-toothed blades.

Bi-metal, in reference to most (if not all) saw blades really means nothing
more than a hard alloy strip for cutting is mated to a softer, more flexible
(and probably cheaper) material that makes up the majority of the width of
the blade.

The hard cutting strip (I referred to earlier as a coping saw blade) section
of a bi-metal saw blade is fused with a softer, more flexible backbone on
quality saw blades.
I've seen the illustrations in literature within the last few years, but
can't locate them now.

I've also seen the mating line between the hard cutting strip and the softer
backbone of quality holesaws and hacksaw blades (which was not the HAZ
transition between induction hardening and the annealed softer backbone of
cheaper blades).

The cutting strip of quality saw blades is a hard alloy, but it's not going
to be full hard HSS (the type of HSS that cuts steels) because HSS doesn't
bend around bandsaw wheels, nor would it be formed into circles from flat
blade stock to fabricate hole saws.

Ed mentioned HSS power hacksaw blades, but Starrett and some others keep
attaching HSS to their bandsaw blade features. There have been many
references to HSS saw blades here in RCM that probably aren't based upon
anything other than the packaging markings.
I believe it's crap, just marketing.

I did just look thru the Lenox online bandsaw material, and didn't find any
mention of HSS in bandsaw blades, but I might've missed it.
http://www.lenoxtools.com/enUS/Products/BI-METAL.html

I don't think I have implied that a carbon steel cutting strip would be
mated with a carbon steel backbone, as you say there would be no reason for
it.
I've maintained that the backbone of the blade will be a softer steel, more
flexible than the harder alloy used for the cutting edge, but not a HSS
cutting edge (because full hard HSS doesn't bend).

I don't own a hardness tester, but if I were to choose, I think a high
carbon steel drill would drill steel better than the annealed shank of a HSS
drill or reamer (properly fluted and sharpened equally).
The reason for my choice would be that the high carbon drill would resist
filing better than the annealed shank of a HSS drill or reamer.

I understand that you were using the hex/allen wrench for an example, but
for cutting those, a hacksaw wouldn't be a choice, only an abrasive disk.

It's a bit confusing when you agree that HSS is brittle, then go on to say
that the cutting edge of a bi-metal holesaw is clearly HSS.
Did it not occur to you that the brittle HSS would snap before being formed
into a circle.

My smallest Millers Falls holesaw is 7/16" and then I have some Lenox in
between, and the big 3" new ones are Starrett, not marked HSS, not marked
bi-metal, but the label reads High Speed Welded Edge. Starrett Safe-Flex
Hole Saw Variable Pitch.
There is a distinctly visible seam about 1/16" behind the deeper gullets,
all the way around the saw.
At the rear edge of the blade there is a wider welded area (looks more like
TIG) to join the circular top arbor plate to the blade. A similar looking
narrower weld joins the ends of the blade to form the circle.

I don't believe this Starrett holesaw is anywhere near the quality of a
commercial shop grade metal cutter, though.. just an example.

--
WB
..........
metalworking projects
www.kwagmire.com/metal_proj.html


"Ned Simmons" wrote in message
...
On Mon, 1 Dec 2008 05:47:04 -0500, "Wild_Bill"
wrote:

I was following you right along John, until you brought up the high carbon
steel hypothesis.

*** Since it's solid carbon steel, shouldn't the entire blade by your
logic
have the
brittle characteristics that the tooth edge does?

High carbon steel is easily annealed, but HSS not so much.
As I said earlier, the saw blade backing (backbone?) material is generally
a
milder steel. It could be similar to steel banding material. It flexes
very
easily and doesn't work harden.

Springs should not, and aren't usually made from brittle materials,
because
they wouldn't serve their purpose.
Generally, when a spring is bent by hand for example, it bends (until the
radius becomes too small, such as around the corner/edge of a vise jaw).

We seem to be approaching the area of modulus of elasticity, which isn't
at
all what I was referring to, as far as HSS being suitable (or even
possible)
for use as a flexible blade material, such as a bandsaw blade.

I'm no metallurgist, but if HSS has a MoE, I'd guess that it wouldn't even
resemble mild steel, and I'm guessing that it would be significantly
different than high carbon steel and/or spring steel.

The modulus of elasticity of all those alloys, in fact all steels,
falls in a very narrow range. But that has little to do with this
discussion.


I remember using some hacksaw blades decades ago, that would snap
completely
thru their width, and I believe they were high carbon steel entirely, with
very little or no annealing of the blade back material, so it was as
brittle
(or nearly as brittle) as the tooth area.
I suspect that these may have been the cheapest blades available at that
time, and
I haven't encountered any hacksaw blades made like that, since then.

Modern, commonly available, general use hacksaw blades are typically a
softer/mild steel back material with a hardened tooth area (generally a
welded section added to the mild steel back material by continuous
welding).
But it's highly unlikely that the hard tooth section is actually HSS, as
HSS
does not bend.

You need to clarify what you mean by "bend." Clearly HSS can bend
without breaking, just like any metal, as long as its ultimate tensile
strength is not exceeded. What's different about fully hard HSS,
compared to materials you might consider "springier" (using that term
very loosely), is that the difference between its yield and ultimate
tensile is very small. In other words, there's not much difference
between how much it can bend and spring back and the point where it
will break, i.e., it's brittle.

The difference between carbon steel hacksaw blades vs. HSS bimetal
blades when cutting difficult materials (SS, alloy steels) is
remarkable. Get yourself a carbon blade from a good manufacturer and a
Lenox (sorry, John g) bimetal blade and try cutting an allen wrench
in half. I doubt you'll make much of a dent with the carbon blade. The
bimetal blade will be a bit worse for the wear, but it will cut the
wrench.

The edge on good bimetal hole saws is clearly HSS -- otherwise the
speed required to run a 3" hole saw in steel without instantly dulling
the teeth would be abysmally slow. If you've ever tried using a carbon
steel twist drill in steel, you'll know what I mean.


To offer an answer to the question "wouldn't/can't the cracking be heard
as
the blade is bent".. well yes, and that's because the tooth area is a
strip
of high carbon steel mated to a flexible back material, but the tooth
strip/area is not likely to be HSS, because solid HSS doesn't bend.

There'd be no good reason to weld a carbon steel edge to a carbon
steel back. If the goal is a hard edge and softer back, then
differential hardening/tempering of the blade will accomplish that,
and is exactly what's done for carbon steel bandsaw blades.

So what good would a bandsaw blade be, if all the teeth cracked at the
tooth
gullets?

As long as the teeth stay attached to the back, I don't see that the
cracks would be a problem.

--
Ned Simmons