On Mon, 1 Dec 2008 14:04:57 -0500, "Wild_Bill"
wrote:
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.
As I said before, you need to be more specific about these terms. If
by "flex" you mean, "deflects then springs back to its original
shape," then HSS does indeed flex. More, in fact, than a softer carbon
steel.
If "flex" means, "permanently deforms before it breaks," then yes, HSS
doesn't flex much. But the first definition fits better with the
everyday sense of flex.
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.
That's exactly where I'm coming from. If blades with independent teeth
work, why does it matter whether they were applied that way, or were
separated by cracking in use?
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.
That's your thesis. No one else has agreed yet.
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.
We haven't determined whether or not the HSS steel on the edge of a
bandsaw blade will bend to the radius of the wheel without fracturing.
The calculation is not difficult -- give it a shot.
As for hole saws, I agree that hardened HSS will not bend to the small
radii required. Presumably the edge is formed before heat treat.
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).
Again, define your terms (bend, flexible).
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.
The carbon steel drill will not retain its hardness unless you run it
at a very low speed. This is not true of good bimetal hole saws.
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.
I've cut many allen wrenches this way when an abrasive saw was not
handy. Lots of box and open end wrenches, too, but they're usually not
nearly as hard as allen wrenches.
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.
It's formed before heat treat.
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.
Clearly a hole saw is not as fussy as an endmill, but that doesn't
mean that the edge can't be made from a similar material. Some spark
testing comparing hole saws with drills or milling cutters might be
instructive.
--
Ned Simmons