Specifications

This situation may result if the adjustable fixed knife is worn or is not parallel to the
trimming action of the movable knife. Check this condition of the adjustable fixed
knife by inspecting the marks left on the surface of the movable knife that is under
the adjustable fixed knife. If the marks are more severe in the area that aligns with
one edge of the adjustable fixed knife, the adjustable fixed knife may need to be
adjusted or replaced, or both. Another method for checking this condition is to
perform the "ink wipeoff test" as described in the steps for adjusting the adjustable
fixed knife later in this chapter.
Under Thread Presser
The under thread presser shown in Figure 4-14 holds the bobbin thread after a
trim. This permits a loop of bobbin thread for the next stitch. While the under
thread presser holds the bobbin thread there should only be enough pressure
applied to hold the thread in place under the movable knife. If the under thread
presser is damaged it can cause problems that look like tension troubles. For
example, if the pressure of the under thread presser against the movable knife is
too much, it may hold the bobbin thread and not allow a loop to be formed, or it
may nick or fray the thread, again making it look like the bobbin tension is
incorrect. Another example, would be if the under thread presser is "crumpled"
(see Figure 4-14), it does not allow the movable knife to pass under the adjustable
fixed knife completely to cut the thread, causing a "no cut" condition. If the under
thread presser is damaged it can cause intermittent long tails of the upper thread.
Under Thread
Presser
(with adjustable
fixed knife
removed)
Figure 4 - 14 Under Thread Presser
Adjustable
Fixed Knife
Movable
Knife
Under
Thread
Presser
Profile of a
damaged
presser
Profile of a
good condition
presser
Under Thread Presser 4 - 17
110279-01, Rev B 4. Trimmer Maintenance