Specifications

Under Thread Presser
The under thread presser, shown in Figure 2-31, 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 2-31), it does not allow the movable knife to pass under the spring 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.
Checking the under thread presser is done in two parts. First by looking at the part
itself to see if there has been any "crumpling" as shown in the bottom left section
of Figure 2-31. Crumpling is damage caused by the movable knife hitting the under
thread presser. If you see visual evidence of any damage, replace the under thread
presser as described in Section 3 of this manual.
Profile when damaged
Profile of good condition
SIDE VIEW
.50"
TOP VIEW
Under Thread
Presser (under
spring knife)
Figure 2 - 31 Under Thread Presser
Spring
Knife
Movable
Knife
Trimmer Option 2 - 37
110305-01, Rev A 2. Service Adjustments