Figure 3-51.--Types of wood screws and nomenclature.
To prepare wood for receiving the screws, you
bore a pilot hole the diameter of the screw in the
piece of wood to be fastened (fig. 3-52). Then bore
a smaller starter hole in the piece of wood that is to
act as anchor to hold the threads of the screw. Drill
the starter hole with a smaller diameter than the
screw threads. Go to a depth one-half or two-thirds
the length of the threads to be anchored. The
purpose of this careful preparation is to assure
accuracy in the placement of the screws. It also
reduces the chance of splitting the wood and
Figure 3-52.--Sinking a screw properly.
reduces the time and effort required to drive the
screws.
The proper name for lag screws (fig. 3-51) is
lag-bolt wood screw. Building construction often
requires you to use these screws. Lag-bolt wood
Properly set slotted and Phillips flat-head and
screws are longer and much heavier than the
oval-head screws are countersunk enough to permit
covering the head. Round-head screws are driven
common wood screw and have coarser threads. The
so the head is firmly flush with the surface of the
threads extend from a cone or gimlet point slightly
wood. The slot of the round-head screw is parallel
more than half the length of the screw.
to the grain of the wood.
Square-head and hexagon-head lag screws are
always externally driven, usually by a wrench. They
Wood screws come in sizes that vary from 1/3
are used when ordinary wood screws would be too
inch to 6 inches. Screws up to 1 inch in length
short or too light.
increase by eighths. Screws from 1 to 3 inches
increase by quarters. Screws from 3 to 6 inches
Dowels
increase by half inches. Screws also vary in shaft
size. Proper nomenclature of a screw is shown in
HTs use dowels to assemble and hold loose
figure 3-51. This includes the type, material, finish,
parts of a pattern in proper relation to each other
while ramming up the pattern. Dowels often
length, and screw size number. The screw size
reinforce glued joints and delicate parts of a job.
number shows the wire gauge of the body, drill, or
Wood dowels are round wooden pins made from
bit size for the body hole. It also shows drill or bit
straight-grained maple or birch. The diameters
size for the starter hole. Tables 3-3 and 3-4 provide
commonly used in the shop range from 1/8 to 1
size, length, gauge, and applicable drill and auger bit
inch, in 1/8-inch increments.
sizes for screws.
3-35
