On Wed, 16 Jul 2008 16:18:10 -0400 (EDT), (J.
Cochran) wrote:

In article ,
Frank Boettcher wrote:

The crown is important. The blade tracks to the usable portion of
each wheel primarily by trying to climb the crown to the apex but
being just on the edge of being able to do so. Without the crown the
blade just keeps going in the direction it is heading, off the edge of
the wheel.

Actually, the blade does climb to the apex. And whenever the blade
is pushed off the apex, the crown causes the blade to tilt slightly
and climb right back to the apex.

The blade running exactly on the center and top of the crown on both
wheels is more a matter of random chance than design. When
manufactured there is a tolerance zone actually measured with a gage
when the machine is "tracked" on the assembly line. If the blade is
within the gage limits on both wheels, that means that the machine
will properly track the largest blade the the machine is designed for.

It is not uncommon for the blade to run slightly off center on both
wheels on opposite sides when the blade is properly tracking.

My comments are on the manufacture of Delta domestically produced
units, I'm not familiar with others but think most are done in the
same manner.

Frank