Thanks guys. I followed Reb's advice and found this:
How do I sharpen table saw blade. Here is the pertinent part.
Dealing With 'Dull Carbide'
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As late as the early 1980's, high speed steel (HSS) router bits and
saw blades were still the norm, and carbide-tipped cutters were
more or less reserved for 'serious' shops. Times have changed,
thankfully, and research into new forms of carbide and new processes
used to manufacture the materials have made carbide the most cost-
efficient cutter material for just about anybody's shop needs.
Strangely enough, though, (at least in my mind), there is still a
rather powerful mystique surrounding carbide tooling which causes most
woodworkers to believe that sharpening dull carbide tipped bits and
blades is something that must be done by commercial sharpening shops.
This couldn't be further from the truth, and I think most people, with
reasonable care, can get much better results by doing the job themselves
than they're likely to get from a sharpening service. I know that's
held true in my own experience.
There are a number of different grades of carbide commonly used in saw
blades, router bits, and shaper cutters, but they all share the basic
qualities of superior hardness, heat resistance, and brittleness. All
require diamond stones to sharpen and hone their edges, but fortunately,
the diamond abrasives needed are not expensive, and for the cost of one
decent router bit, you can buy a pair of diamond hones that will sharpen
dozens of carbide tips many times over. The hones I prefer are called
'paddle hones' -- basically a flat plastic stick, one end of which has
a diamond embedded metal pad attached. Using them is quite straight-
forward, as you'll see shortly.
First, though, it's worthwhile noting that since carbide tools last much
longer than HSS tooling, they have a much greater opportunity to become
fouled by resins and oils that occur naturally in woods. These resins
adhere to the teeth, the heat from friction hardens them, and they actually
may cause a blade or bit to seem dulled, even though it isn't. Your first
course of action, then, should be to examine your carbide tips often, and
clean them regularly. Soaking the tool or blade in a citrus oil soap is
the best method I've found for cleaning cutters. Most solvents will also
work, but the one time I used lacquer thinner to clean some sawblades, it
took the labelling right off the blades in a matter of minutes, and from
that point on I've used the citrus oil route. In any case, a 15 to 30
minute soaking followed by a light scrubbing with a toothbrush or a small
brass-bristled brush will remove any gunk that's likely to be found on your
carbide tooling. You may find that the tool wasn't even dull at all, and
that nothing further is needed for the moment. Note that before cleaning
or sharpening bearing-guided bits and cutters, the bearing should first be
removed so as not to compromise its lubrication.
Should you choose to touch up the edges, it's a very simple procedure. All
carbide router bits and shaper cutters have flat faces supporting the edge.
It's this 'leading' face of the bit, opposite the bevelled, or trailing face
that you want to dress. Take a medium diamond hone, wet it in either plain
water or slightly soapy water, and begin honing the flat face. Don't worry
about the bevel -- with carbide, there is no burning of the bevel and no wire
edge to concern yourself with, so treat it as though you were flattening the
back of a chisel or plane iron. Keep the surface wet, and stop honing as
soon as the surface has a uniform sheen and color, then move on to the next
face. You may be surprised that it only takes a few strokes from the hone to
dress the face, but resist the temptation to continue, or you risk shortening
the life of the cutter by changing its profile. Repeat the honing with a fine
diamond paddle, and if you really want to do the job right, follow up with an
ultra-fine. The edge is not going to feel as sharp as a well-honed high speed
steel edge, and indeed, it won't be. It wasn't when the tool was brand new,
either, and it never will be -- that's the limitation inherent in carbide, at
least for the present. But it will be sharp -- if you've been careful, it will
almost certainly be as sharp or sharper than it was when it was brand new.
For the carbide tips on saw blades, the procedure is almost identical. Hone
the flat, leading faces of the tips, taking care to keep the hone flat against
the face of the carbide. Unlike HSS blades, carbide blades cut along the sides
the teeth as well as along the tips, so be careful not to round these edges over
as you work. Do not attempt to hone the side faces of the carbide tips -- those
edges will naturally sharpen as the face of the tooth is dressed. When you've
finished honing the tooth faces with the fine or ultra-fine paddles, you may
find it necessary to just touch the top of the tooth with the extra-fine hone.
If you choose to do this, again be very careful to just barely polish the carbide.
Any more than that and you risk irreparably changing the shape of the tooth. At
all times, take care to keep the hone flat against the surface you're dressing.
And that's all there is to it. Chances are that your carbide will be every bit
as sharp as it was when new, and it's entirely likely that it will be noticeably
sharper. It's almost certainly sharper than it would be after being ground by a
sharpening shop, and you've removed far less carbide, increasing the life and
accuracy of the tool. Practice on your oldest bits and blades first while you
get the hang of things, and by the time you get around to your best tooling,
you'll be sharpening carbide better, and maybe even faster, than the pros.
So, I'm going to do the wash and then find the diamond paddle hone and give it a shot.
