chipped tungsten carbide chisel....

[Don Dougan <dondougan@zzzzzzzz>]

Green silicon carbide wheels are what you need to sharpen the tungsten
carbide tips.

You do not want to use the bluish-colored aluminum-oxide grinding wheels
that are standard on bench grinders.  Aluminum-oxide grinding wheels are
great for high-carbon tool steel, but the abrasive is not hard enough to
sharpen tungsten-carbide.  Silicon carbide abrasive is harder than
aluminum oxide, but the matrix of the wheel itself is softer ? so it
wears out more quickly with comparable use.  Silicon carbide wheels are
also more expensive than the aluminum-oxide wheels, so though they will
work to sharpen your high-carbon steel tools, it will be more economical
to use two wheels ? one for tool steel, the other for carbide-tipped
tools.

Another thing about tungsten carbide tipped tools ? Do not use water to
cool or quench while grinding!  The buildup of friction heat while
sharpening will not harm the tip, but the thermal shock of quenching can
cause the tungsten carbide to fracture or crack imperceptibly and next
time you start to carve you will soon discover the tool is ruined.

Tungsten-carbide bits will stay sharp a long time, but they are more
brittle than high-carbon tool steel tools.  This brittleness makes them
more susceptible to damage by mis-blows of the hammer or even dropping
them on the concrete floor.  On any stone, but especially so on a stone
like portoro with the wide variations in hardness between the light and
the dark-colored areas, extra care should be taken to keep the cutting
edge in full contact with the stone surface so the stress of each blow is
distributed across the entire tip.

When re-sharpening be sure to retain the relatively blunt angle to which
the point or cutting-edge was originally ground.  If you try to make the
angle sweeter (as you might be used to from your high-carbon chisels)
then you are just going to break the tip even more quickly next time.

If you bought the chisel from Trow & Holden then return it ? I know they
have a lifetime no-questions-asked policy on their hammers ? and they
will probably re-sharpen or replace it.  I don't know if other
distributors are quite so forgiving, though since the tool is as new as
it is they will probably do the same.

Good Carving to You,
Don

Don Dougan
http://www.dondougan.com