Carbide and router bits!
Sorin
There are many grades of carbide out there. Many companies love to list
them as C2, C4, C6. These numbers are refering to the grain of the
carbide. The finer the grade the better the carbide. We used to but
"Carbide" end mills from a supplier and found out that they were twice
as expensive as the HSS tools and lasted less then the HSS tools. After
a while we changed suppliers for our carbide tooling. The new supplier
had a different brand of tools and they were a bit more expensive than
the previous one but the tools lasted 5-6 times longer. We took one of
the old tools and one of the new ones to a local industrial calibration
company that had a high power microscope. What we saw was unbelievable:
The grain on the old tools was about 4-5 times larger than the new one.
That explain everything to us. After that we only purchased micro grain
carbide tools (from a variety of suppliers) and had lots of success with
it. I believe that the router bit industry is a bit slow when it comes
to developing tools. They do not offer enough choices in what type of
carbide you can buy. They feel that they are safe when they call it"
CARBIDE TIPPED". Most people don't understand much of it. As the CNC
routers are becoming more popular every day, the feed rates are
increased and the tools will last less ands less. Eventually this will
force the bit manufacturers to look for solutions and hopefully they
will go to better grades of carbide.
Sincerely,
Sorin Nenu
--
For one the most economical and versatile Cad-Cam packages please visit
us at: http://www.cadcamdistributors.com
Ronald Murray
I did not know. That's a good point. I'm doubtful if asked most router bit
suppliers could even tell you what grade of carbide that they're
selling.Thanks.
ron
Vijay Kumar
micro-grain. Perhaps not micro-grain enough !
Sorin wrote in message <3773795D...@cadcamdistributors.com>...
Ed Bennett
few years I know a bit about tooling and carbides (no pun intended).
Carbides are formed by combining metal powders and carbon under intense heat
(above 2800 deg F). Most often, the metal used is Tungsten but others are
commonly used as well (Titanium, Tantalum, Niobium, Vanadium, Chromium,
Molybdenum, etc.). The resulting powder is sorted by grain size. "Micro grain"
properly describes carbides with a grain size of less than one micron. Smaller
grain sizes generally produce harder carbides. Larger grain sizes are not
"bad", they are just used for different applications. Often, carbides from
different metals are mixed together to achieve properties impossible with a
single metal carbide. For example, adding Titanium Carbide will help increase
resistance to abrasion and wear. Adding Tantalum Carbide will help reduce edge
deformation under high heat.
A binder is added (usually Cobalt and/or Nickel metal powder) to hold the
carbide grains together in a matrix. The resulting mixture is then forced into
molds at extremely high pressure (above 30,000 PSI). These are then called
"tool blanks" and require two firings before they can be ground to final size
and shape. The first, low temperature firing, results in a material that can be
handled without breakage. It is commonly referred to as "pre-sintering". The
second firing is done at high temperatures (2500 to 2900 deg F) and the material
is sintered in a controlled atmosphere. This causes the blank to shrink
dramatically (about 40% in volume) as the binder melts and the carbide pulls
together resulting in an extremely hard and dense material.
The amount of Cobalt binder generally determines the hardness and toughness of
the resulting tool. In general, reducing the Cobalt content increases hardness
and density. However, transverse rupture strength is increased by increasing
the Cobalt content. So, a compromise needs to be made between hardness and
transverse rupture strength. Here's a few examples of how this works on a
typical micro-grain carbide:
Rockwell A Transverse
%Cobalt Hardness Rupture
------- -------- -------
10% 92.0 390,000 PSI
14% 90.5 425,000 PSI
16% 90.8 500,000 PSI
Your typical C2 carbide used for most woodworking tooling is a 94% Titanium
carbide and 6% cobalt binder. It generally has a RA hardness between 91 and 92
and a transverse rupture strength of 275,000 PSI. A manufacturer can, for
example, choose to reduce the Cobalt content to increase the hardness and
therefore the abrasion resistance. But, the tradeoff would be in the transverse
rupture strength. For example, a C3 carbide is typically 94.5% Titanium carbide
and 5.5% Cobalt. It has a RA hardness of 93.1-94.1 but a transverse rupture
strength of only 250,000 PSI. Such a bit might not be adequate for high feed
rates used in CNC machinery.
Ed Bennett
e...@primenet.com
Home of the TS-Aligner
Visit my web site: http://www.primenet.com/~ejb
Philip Lewis
> I'm not a professional tool and die maker but, having run a machine shop for a
> few years I know a bit about tooling and carbides (no pun intended).
Thank you. That is a very informative
piece and I learned alot from it....
Best Regards
Phil Lewis
Ed Bennett
Thanks for your note! A diamond wheel is used to grind carbide, and yes, I
sharpen my own carbide endmills. I am not sure what the mold material is but
it's likely an air hardening tool steel like S7 or maybe even D2 (as I said,
I'm not a tool/die maker!). It just needs to have a high compression strength
(and a large cross section!).
Ed Bennett
e...@primenet.com
Home of the TS-Aligner
Visit my web site: http://www.primenet.com/~ejb
RWatson767 wrote in message <19990628214137...@ng-fk1.aol.com>...
>Ed
>>Re: Carbide and router bits!
>
>Throughly enjoyed you post on Carbide. Just one question? One you have the
>blank what kind of wheel do you use to make the final cuts? And what is the
>mold material?
>Thanks
>Bob AZ
