Timken Industrial Seal Catalog

Engineering Data
Comparing Shaft Lead – Lead Angle
The lead of a shaft is compared with other shafts of
differing diameters by calculating the lead angle. This
is found by dividing the string advance (in inches) by
the product of the shaft circumference (in inches), and
the number of revolutions required to advance the
string the measured amount.
LEAD ANGLE = ARCTAN x String Advance
(Shaft circumference) x (number of turns)
For example, a string will advance 0.300" in 30 seconds
on a 4.000" shaft rotating at 60 RPM. The lead angle
equals 0.0456° = 2' 44.1". A 2" shaft with the same
advance (0.300" in 30 seconds at 60 RPM) has a lead
angle of 0.0912° = 5' 28.3".
For best seal performance, industry standards recommend
that the lead angle of a shaft be 0° +/- 0.05° (+/- 3').
Figure 1: Clockwise Lead
Figure 2: Clockwise Lead
Engineering Data
Shaft-to-Bore Misalignment
Shaft-to-bore misalignment is the distance by which
a shaft is off center relative to its bore. To measure
this, calculate the distance between the shaft center
line and the bore centerline, as shown in Figure 5.
Shaft
Shaft
Figure 3: Counter-Clockwise Lead
Figure 4: Counter-Clockwise Lead
“X” = Shaft-to-bore Misalignment
“X”
Bore
Bore
Figure 5: Shaft-to-bore Misalignment
3