Wood screw

An improved wood screw which is self drilling. The wood screw has a first spiral flute that extends essentially the full length of the screw. The screw also has a second spiral flute which begins at the point of the screw and which terminates a short distance from the point.

BACKGROUND OF THE INVENTION 
The field of the invention is wood screws and the invention relates more 
particularly to wood screws of the type which do not need to have a pilot 
hole drilled therefor. 
Numerous attempts have been made over the years to facilitate the fastening 
of wooden objects. A novelty search revealed the suggestion of the 
addition of a spiral flute at a very early time. Such concept is shown in 
the U.S. Pat. Nos. 45,133, 142,112, 877,131 and 1,235,626. In spite of 
these early attempts, such screws have not found widespread use although 
the need for eliminating the time and inconvenience of drilling a pilot 
hole persists. 
It is well known that simply driving a wood screw into wood without the 
provision of a pilot hole, particularly in hardwood, almost invariably 
results in the splitting of the wood. It also is very difficult to start 
the wood screw in a straight line. 
SUMMARY OF THE INVENTION 
It is, thus, an object of the present invention to provide a wood screw 
which does not require a pilot hole and which is easily started and 
continued into the wood. 
The present invention is for an improved wood screw of the type having a 
head, a shank and threads having exceptionally easy starting and insertion 
ability. The screw has a first spiral flute passing essentially the full 
length of the screw. A second spiral flute begins at the point of the 
screw but continues only a short distance therefrom. The shape of the 
second spiral at the tip is about the same shape as the first spiral at 
the tip, so that the tip is symmetrical, starts immediately and does not 
tend to wander when started. Preferably, the screw also has cutting means 
along the undersurface of the head of the screw so that it is also self 
countersinking.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A wood screw which is self drilling is shown in FIG. 1 and indicated 
generally by reference character 10. Wood screw 10 is of the type 
generally referred to as a lag bolt and has a hexagonal head 11, a shank 
12, a spiral thread 13 and a root 22 at the base of the thread. The point 
of the screw 13a has a drilling surface formed therein shown best in FIG. 
4. The drilling surface is created by a first spiral flute 14 which 
extends essentially the full length of the screw and a second short flute 
15 which extends only a short distance from the tip. The point 13a is, 
thus, shaped very much like a common drill having a pair of flutes and a 
pair of cutting edges which might be referred to as edges 16 and 17 in 
FIG. 4. Because of this, when the screw is placed on a surface of wood 
such as surface 18 of wood block 19, wood screw 10 readily drills a pilot 
hole for itself, and the wood cuttings 20 are conveyed upwardly as 
indicated by arrow 21 in FIG. 2. 
The shape of the spiral flute 14 is shown in FIG. 3. There the 
cross-sectional shape of flute 14 can be seen to be approximately one 
semicircle with respect to the root 22. The depth "d" of flute 14 is 
approximately one-third of the diameter "D" of root 22. The depth of flute 
14 should not be such that it significantly weakens the strength of screw 
10, while it should be sufficiently deep so that it is capable of 
conveying the wood cuttings to the surface of the wood. A distance of 
about one-third of the root depth has been found appropriate for this 
purpose. 
The angle of the spiral with respect to the longitudinal axis of lag screw 
10 is indicated by angle "a" in FIG. 2. This angle should be about thirty 
degrees to properly convey the wood cuttings from the pilot hole drilled 
by the screw, itself. The angle should not be so great as to tend to drive 
the wood screw into the wood, but a certain amount of spiral is 
appropriate to assist in conveying the wood cuttings upwardly. 
A flat headed screw is shown in FIG. 5 and indicated by reference character 
23. Screw 23 has a flat head 24, a shank 25, a point 26 and a spiral flute 
27 which extends essentially the full length of the screw. A second flute 
28 begins at point 26 and extends through about three thread crests such 
as thread crest 29. The two flutes are shown in FIG. 7 and, again, it can 
be seen that point 26 is symmetrical and has a pair of cutting edges 30 
and 31. 
Screw 23 has a second feature which facilitates counter-sinking head 24 to 
a point where it is even with the wood surface. This comprises a plurality 
of cutting grooves 32, 33 and 34. Groove 34 is shown in cross-sectional 
view in FIG. 8 and serves to cut into the wood and to spread the wood 
cuttings outwardly as the screw is turned. 
The angle of spiral flute 27 is indicated by "b" in FIG. 5 and once again 
is approximately thirty degrees with respect to the longitudinal axis of 
flat head screw 23. 
It has been found beneficial to utilize a phillips head type of head 
because of its tendency to hold the screwdriver point along the axial 
center of the screw. It has also been found beneficial to utilize power 
tools to drive a hex head screw such as wood screw 10, and this also tends 
to hold the screw in a vertical desired orientation. 
The resulting wood screw of the present invention may be made in various 
sizes and for various purposes. The wood cuttings in the long spiral tend 
to be compressed and create an exceptionally strong fastening quality of 
the screw in the wood. The spiral flute through the threads act as a tap, 
cutting clean threads in the wood rather than compressing and splitting or 
weakening the material. It has been found that wood screws made according 
to the present invention will penetrate through knots while reducing the 
danger of splitting the wood, even near the ends of the material. The 
shape of the point of the screw removes just enough wood to allow the 
screw to be started without creating the wedge effect of a normal wood 
screw. By not having to drill a pilot hole, labor is saved, and in many 
locations it is difficult to bring a drill to the work site and, thus, 
this step is also eliminated. The principle of the present invention 
applies not only to small wood screws, but also to large lag bolts as 
shown in the drawings. 
The present embodiments of this invention are thus to be considered in all 
respects as illustrative and not restrictive; the scope of the invention 
being indicated by the appended claims rather than by the foregoing 
description. All changes which come within the meaning and range of 
equivalency of the claims are intended to be embraced therein.