Re: [CAD_CAM_EDM_DRO] Re: brittle cutters

Hi Rich:
As Jon pointed out, carbide is not case hardenable.
What you may be seeing, is a coating on the carbide.
Titanium carbonitride is black (I think). So are some diamond coatings.
Some of these coatings are deposited at high temperatures and can affect the
microstructure of the carbide underneath.
When the cutter is really skinny, the substrate can become embrittled and
microcracked from the high deposition temperature and the subsequent
cooling.
The best material for cutters I've ever found, is the shanks of broken off
carbide endmills.
Tiny cutters usually break before they wear out, so lots of them end up
snapped off and sitting in a box in almost any toolroom.
They have 1/8 shanks, and the carbide is excellent quality micrograin...much
better than most blanks you can buy.
You need a really fine diamond wheel to take full advantage of them though.
Something like 600 grit is right for finishing cutters.
Carbide is so brittle that any stress risers will initiate cracks very
quickly, and lead to failure of the tool.
On engraving cutters, it's usually edge chipping followed by overload and
snapping off of the whole tip.
Cheers

Marcus

----- Original Message -----
From: "RichD" <cmsteam@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Monday, October 14, 2002 8:23 PM
Subject: Re: [CAD_CAM_EDM_DRO] Looking for spindles [cutters]


> CL,
> Speaking of engraving bits. Last week I finally discovered the answer to
why,
> after several sharpenings, the edges on Antares "solid micrograin carbide"
cutters
> would instantly break down when touched to metal in the usual operation.
> After many repeated resharpenings and microscopic examination, the
evidence struck
> me. What I noticed was a difference in color between the unground surface
flat, dark,
> and the core metal, much lighter. These cutters are case hardened. Once
you grind back
> to the core material, they chip and crumble very easily. Trash!
> A new cutter performs as expected, even with their crude sharpening. It
appears as
> tho they are case hardened after sharpening.
> I bought the carbide tipped type. I have asked them about all carbide
cutters, but no
> reply as yet.
> This unexpected problem has cost me many hours of lost time and product
not up to my
> full expectations.
> Beware of this situation, should you encounter edges that don't seem to
last like they
> used to.
> RichD
>
> CL wrote:
> >snip
> Most spindles like this use a top loading style bit which can be real
handy for toolchanges. They
> come in "fixed" diameters for 1/8', 11/64" and 1/4" tooling. A picture of
a typical bit is on the
> > top of the Antares Page: http://www.antaresinc.net/ Many types of bits
are available including spiral flutes and oversize fly bits. Most of the
bits are easily sharpened if you are fortunate enough
> >snip
> >
>
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