Brush Stiffness
Effect of Caliper and Trim Length
There are many combinations of filament diameter and trim
length that will result in a brush with similar stiffness.
Figure 4 presents this information graphically. For example, let
us suppose a given brush has a trim of 2 in and is filled with
10-mil (0.010-in) filament. Draw a line on the chart from 2 in on
the trim length scale to 10 mil on the diameter scale. Note where
this line crosses the reference line. Assume that a new brush
with a 2 ½-in trim length and the same stiffness is required.
Draw a line from this point on the trim length scale through the
crossover point on the reference line to a new diameter. In the
example shown on the chart, the line is drawn to the diameter
scale at 14 mil. Therefore, assuming the filling material used is
the same, a brush with a 2 ½-in trim filled with a 14-mil filament
will have the same stiffness as the original brush with a 2-in trim
filled with 10-mil filament.
The answer is only an approximation because tuft stiffness is also
affected by the way in which the brush is made (i.e., staple set,
wire drawn). Also, because tuft stiffness is a function of the 2nd
power of the filament diameter, even a small deviation will have
a large effect on stiffness. This chart can be used for any type of
level filament as long as both brushes are filled with the same
type of filament.