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TM 9-254
Section V. INSTALLATION OF HELICAL INSERTS AND REMOVAL OF DAMAGED SETSCREWS
3-9.
Helical Inserts.
a.
General. Helical inserts are used to prevent a hard steel bolt or screw from damaging the threads in softer
metal such as aluminum castings.
b.
Installing Helical Inserts. Helical inserts are sized according to the diameter and number of threads per inch.
Select the appropriate size helical insert and install as follows:
NOTE
o
For a blind hole, the length of insert must be selected to insure that a clearance of one-eighth
of an inch exists from the bottom of the hole to tang of the insert.
o
For a through hole, the length of insert must be selected to insure that the tang of the insert
mounts flush with the bottom of the hole.
(1)
Retract the mandrel of the helical inserting tool (fig. 3-26) and place a helical insert into the chamber with
the tang end of the insert toward the chuck.
(2)
Advance the mandrel until it fully engages the insert tang. Continue turning the mandrel, advancing the
insert into the chuck until the mandrel and insert are flush with the tip of the chuck.
(3)
Hold the inserting tool firmly and squarely against the work with the insert alined with the tapped hole
(fig. 3-27).
(4)
Rotate the handle clockwise at a slow uniform rate until the top coil of the insert is 1/4 to 1/2 turn below
the top work surface of the hole.
(5)
Rotate the handle counterclockwise to remove mandrel from hole.
(6)
Place the punch end of tang break-off tool (2, fig. 3-28) into the center of the insert, resting the tool
squarely on the insert tang.
(7)
Strike the top of the tool with a sharp blow using a soft-faced hammer to break tang from insert.
(8)
If needed, use long narrow tweezers to remove the tang from insert hole.
c.
Extracting Inserts (fig. 3-29). Helical inserts must be removed when they are bent, broken or improperly
installed. To remove an insert:
(1)
Position the blade of the extracting tool into the center of the insert.
(2)
Tap the top of the extracting tool with a hammer to seat the tool into the insert.
3-26
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