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Carbide Cutterheads for Jointers

Cut manufactured
materials and
make fewer
knife changes

By Dave Munkittrick

The latest thing in jointers
is the segmented carbide
insert cutterhead. Instead of
high-speed steel (HSS) knives, the cutterhead
is peppered with an array of solid-carbide
inserts (photo at right). During our 8-in. jointer tool
test, we had a chance to
compare these new cutterheads head-to-head with their straightknife
cousins. We like what we saw and now use some of them in
our shop. They’ve received unanimous thumbs-up from all users.
Carbide took over in a hurry when it was introduced on saw blades,
router bits and shaper knives. I wouldn’t be surprised to see the
same trend occur with jointer and planer knives.



At $300 to $400, segmented carbide cutterheads aren’t inexpensive.
But consider the cost of sharpening HSS knives (about
$15 a set) and the need for an extra set of knives to replace the
ones being sharpened (about $30). On average, the initial additional expense of a segmented carbide cutterhead is
about the same as the cost for 20 HSS knife sharpenings,
so you’ll eventually recoup your investment on
the carbide model. With a segmented cutterhead, you
basically pay up front for sharpenings but you get to
enjoy all the benefits of carbide right away.

Replacing the inserts after all four edges are dull
will cost $120 to $200, depending on the number of
inserts in the head and the cost of each insert.


Changing inserts

Rotating or changing the inserts is a somewhat
tedious but straightforward task. You must be meticulously
clean when changing or rotating inserts. Even a
little sawdust under one insert can leave an uneven cut.


Segmented cutterheads take more power

I’ve noticed that the segmented cutterheads take
more feed pressure and demand more horsepower
from the jointer. According to Curt Wilke of Wilke
Machinery, which distributes several brands of jointers,
this is because the segmented cutterhead always
has several inserts cutting at any given time. A standard
straight knife has an impulse cutting action.
Each knife takes its cut with a rest period between.

Click any image to view a larger version.

A segmented
carbide cutterhead
has 40
to 60 individual carbide inserts bolted
onto it. Each insert has four sharp edges that
can be rotated when one side becomes dull.

Carbide cutters allow you to joint abrasive manufactured materials,
such as plastic laminate, melamine, particleboard and MDF.
These materials would destroy the edge on a set of HSS knives.

Changing carbide inserts is done less frequently and is less frustrating
than with HSS straight knives. It still takes time, about a minute
per insert, but with none of the headaches that come with setting
straight knives. Just unbolt an insert, clean off any pitch, rotate the
insert 90 degrees to a fresh edge and bolt it back into place. If you get
a nick in the cutterhead, move a few of the nicked inserts to new locations.
The cuts overlap and will clean up nicks in any individual insert.

5 Big Advantages

1. Longevity. A single set of carbide inserts will outlast a conventional
knife set by approximately 40 times. That’s because each
insert is made of solid carbide and has four cutting edges.
Each edge will last up to 10 times longer than a typical HSS
knife-edge. Multiply that number by the four edges on each
insert and you get 40 conventional knife sharpenings built in
to each set of carbide inserts. Remember that when you’re
weighing the extra cost of a segmented carbide cutterhead.

2. Jointing manufactured materials.
Carbide inserts allow you to joint manufactured materials,
such as melamine and MDF, which would instantly dull HSS
knives (photo at left). This is true of hard abrasive woods
like teak, too.

3. Easy knife changes.
With carbide inserts, knife changes are no longer such an
onerous task. No more fussing with knives
that creep out of position as they’re tightened down.

4. Less noise. A segmented cutterhead runs noticeably quieter than a
straight knife cutterhead. Anything that diminishes the noise
pollution in the shop is a welcome addition.

5. Quality of cut. Carbide inserts will make clean cuts much longer than HSS
knives will. We found that both carbide inserts and HSS
knives make beautiful cuts when the knives are sharp.
However, the performance curve drops off rapidly with the
HSS knives simply because they dull more quickly.

This story originally appeared in American Woodworker September 2005, issue #116.

September 2005, issue #116

Purchase this back issue.


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