US 1238636 A
Description (OCR text may contain errors)
c. L. CHRISTOFFERSON.
APPLICATION FILED JUNE 5.1916.
Patented Aug. 28, 1917.
CHARLES L. GHRISTOFFERSON, OF WAUKEGAN, ILLINOIS.
Specification of Letters Patent.
Patented Aug. 28, 1911?.
Application filed June 6, 1916. Serial No. 102,010.
To all whom it may concern:
Be it known that I, CHARLES L. CHRIS- TOFFERSON, a citizen of the United States, residing at Waukegan, Illinois, have invented certain new and useful Improvements in Screws, of which the following is a specification.
This invention relates to wood screws and more particularly to that type which are designed to be self-countersinking. Ordinarily screws of this type present numerous disadvantages, one of which is the liability of the throats of the cutters to become clogged with the wood shavings removed by the cutter. It is one aim of the present invention, there fore, to provide the head of a screw of this type with cutters so constructed and arranged that the material removed by the cutters may readily pass out through the throats provided for this purpose, thereby permitting of the screw being continuously threaded forwardly when being screwed into place and obviating the necessity of turning the screw back one or more times in order to remove the material which has lodged in the throats.
Another disadvantage usually presented by screws of this type is that the cutters are so constructed that the wood near the surface is liable to be splintered, thereby marring the appearance of the surface and requiring the use of wood filler. The invention, therefore, has as a further aim to so construct the cutters that the wood will be out in such a manner as to entirely obviate the splintering of the same so that the surface of the wood will remain intact.
Ordinarily screws of this type present the further disadvantage that the cutters and associated throats are so formed as to weaken the head of the screw so that if considerable force is required in driving the screw, one side of the head is liable to be broken off. Therefore, the invention aims further to so form the cutters and associated throats that the head of the screw will not be materially weakened.
A further aim of the invention is to provide a screw of this type which may be cast or otherwise manufactured at practically the same cost as the ordinary Wood screw although of such form as to be self-countersinking.
In the accompanying drawings:
Figure 1 is a plan view of the head of a screw constructed in accordance with the present invention.
Fig. 2 is a bottom plan view of the said head, the shank of the screw being shown in section.
Fig. 3 is a detail side elevation of the head end of the screw.
Fig. 4C is a vertical transverse sectional view through the head end of the screw.
In the drawings the shank of the screw is indicated by the numeral 1 and is threaded in the usual manner as indicated at 2. The head of the screw is indicated in general by the numeral 3 and is provided with the usual transverse groove 4 to receive the bit of a screw driver. As is ordinarily the case in screws of this type the upper face of the head is flat and the head is of inverted frusto-conical form.
In order that the material removed by the cutters, which cutters will be presently more specifically described, may be conducted away from the countersink as the countersink is formed, the conical surface of the screw head is formed with throats indi cated in general by the numeral 5. Each of the throats 5 is preferably of the same width throughout its length and has parallel side walls and a concave inner or bottom wall 6 to permit of more ready clearance of the material passing through the throat and by reference to Figs. 1, 2 and 3 of the draw ings it will be observed that the throats are inclined, the upper end of the throats being located at diametrically opposite points with relation to the circle described by the upper face of the head and at points peripherally midway between the ends of the groove 4 in the said head, the lower ends of the throats being also located at diametrically opposite points. It will further be observed by reference to Figs. 2 and l of the drawings that the throats are gradually decreased in depth from their upper to their lower ends so as to further provide against choking of the throats. The outer edge of the rear wall of each throat in the direction of rotation of the screw when being threaded into the material is sharpened to form a cutting edge and is indicated by the numeral 7, this edge being continuous or unbroken so as to act upon the material with a paring cut.
The present invention contemplates further so forming the head that the material will first be cut into slivers which are subsequently pared from the material as the countersink is formed, through the action of the paring edges or cutters 7 and 111 011161 that the material may be slivered as stated,
the conical surface 3 of the head is formed with two sets of slivering blades 8 which extend spirally along the said surface. The blades 8 of each set have their upper or rear ends terminating at that wall of the throat 5 opposite the wall the edge of which constitutes the paring edge 7, and the blades extend, as stated, spirally, and downwardly from their said ends and have their opposite or forward ends merging into the surface of the said head 3. In other words,the blades of each set extend around the conical surface of the head of the screw from the related throat 5 approximately three-fourths of the distance between this throat and the other throat 5. Furthermore, it will be observed by reference to Figs. 2 and a of the drawings that the blades 8 gradually merge at their forward ends into the conical surface of the head 3 so that they may gradually enter the material in order to cut the material into slivers, which slivers as they are out are received between the blades of each set and are subsequently pared by the edge 7 of the respective throat 5 and as they are so pared and severed are allowed to pass upwardly and out through the upper ends of the throats.
In order that the paring edges 7 may the more effectually perform their function the side walls of the throats 5 while being parallel to each other as above explained, are not disposed in such manner that the edges of the said side walls which are presented at the face of the head 3 are at right angles to the longitudinal median line of the groove 4, but, on the other hand, the said side walls of the throats are not only inclined but are disposed at an angle to the planes of the side walls of the said groove L.
It will be observed by reference to Figs. 2, 3 and 4 of the drawings that the sliver cutting blades 8 are spaced apart so that there are provided relatively wide valleys 9 lying between the said blades, the valleys being increased in width gradually in the direction of the minor or merging ends of the said blades and these valleys permitting of the ready discharge of the slivers which are cut by the said blades. In order that the head of the screw may readily enter the wood as the screw is driven into the wood and the wood is cut away by the sliver cutting blades and paring blades of the said head, there is provided a pair of downwardly projecting blades indicated by the numeral 10, these blades extending circumferentially of the under side of the head the outer edge thereof and each extending from one of the throats 5, a suitable distance in the direction stated. It will be understood that inasmuch as the cutting edges of the blades 10 are presented downwardly, these blades will cut into the surface of the wood and the slivers cut thereby will be removed by a paring edge 11 formed at thesaid side of the respective throat. Thus splintering of the wood at its surface is prevented and the screw head is caused to closely fit within the opening or countersink cut by the said head of the screw. The paring edge 11 is formed by providing the flat upper surface of the head of the screw with a beveled or inclined surface 12, as clearly shown in Figs. 1 and l of the drawings.
Having thus described the invention, what is claimed as new is:
1. A screw having its head formed with a chip throat and provided at one side of the throat with a paring cutting edge and at the other side of the throat with sliver cutting means. g i
2. A screw having its head formed with a conical under surface, the said surface being formed with a chip throat and being provided at one side of the throat with a paring cutting edge, the surface at the other side of the throat being provided with a plurality of sliver cutting blades extending spirally head, and merging into the said surface of the head at their ends remote from the throat.
4:. A screw having a conical head formed with an inclined chip throat gradually increasing in depth in the direction of its outlet upper end, the outer edge of one side wall of the throat constituting a paring cutting edge and the head being formed with a plurality of sliver cutting blades extending from the opposite side wall of the throat ne substantially circumferentially of the 5. A screw having its head formed with an inclined chip throat and provided at one side of the throat with a paring cutting edge, the head being formed with substantially direction of their ends Which are presented in the direction of rotation of the screw the said head being further provided with a depending circulnscribing cutting blade having a downwardly presented cutting edge.
In testimony whereof I afiix my signature.
CHAS. L. CHRISTOFFERSON. [1,. 2.]
spirally extending sliver cutting blades, the paring edge and the cutting edges of the sliver blades being located within the bounds of the conical surface of the head, the sliver 5 cutting blades extending from the last-mentioned side of the throat part-Way around the said head and decreasing in depth in the Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. G.