Civil Engineering Reference
In-Depth Information
This poor axial-load performance can be countered (to a degree)
by using more than one anchor to support the load (as in a ceiling-
mounted traverse rod, for example).
Holes for plastic expansion anchors are best bored with a twist
or push drill in both plaster and gypsum board to get an accurate fit.
Holes jabbed with an ice pick, screwdriver, or similar tool are seldom
sized correctly for the best friction fit and may have considerable
material knocked away from the edge of the hole, inside the wall,
making the site useless for an anchor. Bore the hole the diameter
specified on the anchor package and use the screw size specified
there, also. The length of the screw should be equal to the length
of the anchor, plus the thickness of the object to be fastened, as
a minimum. As a rule, sheet-metal screws work better in plastic
anchors than do wood screws, possibly because their comparative
lack of body taper causes a more effective expansion of the anchor.
Hollow Wall Screw Anchors
These devices are manufactured by a number of different companies.
They consist of a metal tube having a large flange at one end and an
internally threaded collar at the other. A machine screw is inserted
through a hole in the flange, extended the length of the tube, and
screwed into the threaded collar (see Figure 1-29).
In use, a hole of specified diameter is bored through the gypsum
board or plaster. An anchor (see Table 1-14) of the proper grip range
(depending on the thickness of the drywall or plaster) and screw size
MACHINE SCREW
FLANGE
DISTANCE SHOULD BE
EQUAL TO APPROXIMATE
THICKNESS OF WALL
FACING.
BODY SEGMENTS,
WHICH BEND AS
SCREW IS TURNED
THREADED
COLLAR
Figure 1-29
Two sizes of hollow wall screw anchors.
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