On Wed, 15 Oct 2003 22:07:57 -0400, "Robin S."
wrote:


"Gunner" wrote in message
.. .
On 15 Oct 2003 14:49:56 -0700, jim rozen
wrote:

I tend to use a lot of HSS with my lathes and shapers, and have a
decent Baldor grinder with a set of diamond wheels. Ive played with
both, and the HSS wins 90% of the time under normal turning,
particulary if you can flood cool with oil.

What's normal turning? I would think facing and turning as opposed to
grooving and forming. In this case, why does HSS *win*? With what little
experience I've had in toolmaking, radius tools are constantly used along
with other form tools. In this case, carbide is a loser. However, I don't
see why anyone would use anything _but_ carbide for turning/facing.
Esspecially with high carbon, high alloy tool steels and machine steels
(like 41freakin'40).


I turn a lot of O1, 4140 etc with HSS. Its quite true that it dulls
MUCH faster than a proper grade of carbide, but then, carbide dulls
much faster than a proper grade of ceramic, which dulls faster than
diamond. G

It all goes back to having a rigid machine, able to force the carbide
into the workpiece.

I liken it to this: You can cut hardwood, easily with a very sharp
chisel, or you can hammer it in with a dull one. Carbide is in its
element, when you are making hard contact and are cranking out hot
blue chips. This is simply not possible with many/most small flexible
HSM lathes. Something of interest for you to try.... get a hard turn
going, nice blue chip load, good sounding cut with carbide, and turn
off the lights. You will note that in most cases..the cutting
interface is glowing red. That red heat is caused by friction of the
workpiece being forced by the duller carbide tool. Make the same doc,
same feed with a properly sharpened HSS bit, and it will likely not be
glowing, and the chips will likely not be blue.

Again carbide comes into its own, when the workpiece is hard. When you
are approaching the hardness of HSS, yes..carbide wins hands down, for
same doc/sfm.

Some materials simply will not "shear", but must be softened then
ripped off the parent body. Inconel is one such. You MUST have a hard
contact, lots of force, or the heat of the contact will work harden
the material. You MUST be ahead of the heat treating zone when digging
in or it turns to **** on you. Ive cut inconel with HSS. It cuts ok,
if you find that magic angle/doc/sfm, but it wears out HSS quickly.
Let it heat treat itself, get behind the cutting curve and it
instantly gets nearly as hard as the HSS tool itself. Even Carbide has
a hell of a time cutting it at this point. You have to dig in deep
enough to get under that heat treated zone.
This is only true if you
keep your tools sharp, which is labor intensive. Which is one of the
reasons production shops use a Lot of carbide, because they have rigid
machines and labor is a significant part of production costs.

HSS can be run as efficiently as carbide if kept sharp?

Define efficently. Can the cheaper HSS do the same cut as carbide in
most common materials? Yes, indeed. It will do it (Sometimes slower
and shallower), and with less cutting force needed. Other times, it
actually does it faster than carbide.

Carbide is much more brittle than HSS. Interuppted cuts kills carbide
in the blink of an eye, as does chatter. I have both carbide and HSS
cutoff tooling. If cutting off something..I get some sudden chatter, I
will immediately pull out the carbide tool and look at the edge for
damage. With HSS, I simply dig in a bit harder.

When cutting some materials, such as plastics..a very very sharp
positive rake on a HSS tool, cuts that plastic like it was air, even
in huge DOC. Carbide on the other hand, tends to melt it, smear it and
make a huge mess.

I have a good number of plastics houses that cut almost exclusivly
with hand sharpened HSS in their CNC machines for this reason. They
only go to carbide for phenolics, G10 composits etc because the
material itself is abrasive as hell, and they are needing longer tool
life that only carbide or diamond/ceramics gives them. And they are
willing to pay the price for less downtime in sharpening costs and a
worse surface finish.

I also service machines in Swiss screw machine houses. They use a
mixture of HSS and carbide, depending on the material, how many
hundreds of thousands of parts to be cut and the detailed features. In
many of those shops, HSS is cut under a microscope for form tooling,
where a groove may be .005 x .1 deep for example. Carbide (some
grades are better than others) tends to bust like crackers when
subjected to this kind of loading. Shrug.

Efficency is a big variable and you will have to narrow your
parameters a bit for a better answer.

Just keep in mind..that we are discussing here, HSM usages, rather
than production quantities of thousands, and when one can grind a HSS
tool to the proper angles and degrees, its often a hell of a lot
cheaper and quicker than ordering out a $20 insert . Simply put..it
can be more efficient than carbide in many applications. And Id dare
say, in MOST HSM applications..it IS more efficient than carbide,
given price alone.

Gunner


Regards,

Robin


"You cannot invade the mainland United States. There would be a rifle
behind each blade of grass." --Japanese Admiral Isoroku Yamamoto