the "Top Dead-Center"
Next, unplug the jointer.
Now press the start button on the jointer a couple of times to be
sure it is off. Now you need to find the maximum height of the knife
during its rotation. This is often referred to as "top dead-center."
This precise measurement can sometimes seem impossible to find,
but don't worry about getting it absolutely perfect.
To find the top dead-center
(or some place reasonably close), lower the outfeed table about
1/16". Then place a flat, steel ruler on the outfeed table
and partially across the cutterhead. Rotate the cutterhead backward
until the knife does not contact the ruler (photo 1). Using a pencil,
make a mark on the jointer fence just above the front edge of the
ruler. Now slowly rotate the cutterhead forward until the knife
touches the ruler. You will notice that the ruler rides with the
knife (moving towards the right).
Continue rotating the
cutterhead forward. When the knife stops moving, place another mark
on the jointer fence at the top edge of ruler. Now, remove the ruler
and measure the distance between the two marks. Place another mark
on the fence in the center of the two lines (photo 2).
Now, rotate the cutterhead
backwards so that the knife edge is not touching the ruler. Place
the edge of the ruler on the left most mark. Now, rotate the cutterhead
until the ruler is moved to the centerline. This should be reasonably
close to top dead-center.
Use light finger pressure
to prevent the cutterhead from moving as you remove the ruler and
place it against the fence on the infeed table of the jointer (photo
3). Slide the ruler up to the knife edge and use the magnetic hold-down
jig to keep the ruler from moving (photo 4.) Note that the ruler
should not be pinched between the fence and the magnetic jig or
clamp. The ruler should be in front of the jig.
If you don't have the
magnetic jig, clamp a block of scrap wood to the fence against the
rulers edge (photo 5).
Now you should raise
the outfeed table by 1/16" (back to its original position.)
Remove the ruler without
disrupting the magnetic jig (or clamp). Remove the knives and sharpen
them. Don't misplace the springs.