Improvements in the Manufacture of Twist Drills.
Year: 1890

page_text: Date of Application, 3rd June, 1890-Accepted, 19th July, 1890
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Twist Drills.
I, JEROME CARLTON TAFT, of No. 10 West Clifford Street, Providence, Rhode
Island, United States of America, mechanic, do hereby declare the nature of my
invention, and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement :-
My invention relates to the method of manufacturing twist-drills wherein
opposite longitudinal grooves are first formed in the drill-blank, and then twisted to
spiral form; and my invention consists in first forming the opposite longitudinal
clearing-grooves with opposite longitudinally flattened or depressed surfaces between
them, then twisting the grooved blank to spiral form, and then compressing the
metal at the cutting corner or edge of the grooves, to improve the quality of the
drill, and reduce the same to a uniform diameter, as hereinafter fully set forth.
Fig. 1, represents a side elevation of the drill-blank at a stage in the manufacture
of the same, at which the straight clearing-grooves, and the intervening flattened or
depressed surfaces have been formed.
Fig. 2, represents an enlarged cross section taken in the line xx, of Fig. 1.
Fig. 3, represents a subsequent stage in the manufacture at which the grooved
drill-blank shown in Fig. 1, has been twisted so as to impart a spiral form to the
clearing-grooves and intervening flattened or depressed surfaces.
Fig. 4, represents an enlarged cross section taken in the line ax, of Fig. 3.
Fig. 5, represents a side view of the finished drill provided with the compressed
cutting corners or edges according to my improvement.
Fig. 6, represents an enlarged cross section taken in the line xx, of Fig. 5.
In the accompanying drawings, A Fig. 1, represents a drill-blank as heretofore
employed in the manufacture of twist-drills, the said blank being provided with the
straight longitudinal clearing-grooves a, a, and the intervening flattened or depressed
surfaces b, b, as shown in the enlarged cross-section Fig. 2; and A¹, Fig. 3,
represents the drill blank A, when the same has been twisted so as to impart the
required spiral form to the grooves a, a, and the intervening surfaces b, b.
The twisting of the drill-blanks when of small and medium size, is commonly
performed without the application of heat, and in that case the metal at the cutting
corners or edges c, c, of the clearing-grooves, will be deteriorated by the stretching
tension to which it has been subjected in the operation of twisting, and it is the
object of my improvement to restore the original quality of the metal at the said
cutting corners, and I accomplish this result by compressing the said corners in
suitable dies, or between suitably grooved rolls, whereby the metal at the cutting
corner or edge c, will be compacted as shown in Fig. 6, thus improving the lasting
qualities of the cutting corner of the drill and at the same time reducing the drill
to the proper standard size.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:
The method of making twist-drills, which consists in first providing the blank with
opposite longitudinal clearing-grooves having opposite longitudinally flattened or

page_text: depressed surfaces between them, then twisting the grooved blank to spiral form
and then compressing the metal at the cutting corner or edge of the spiral grooves,
as set forth.
Dated this Sith 1..
1900
JEROME CARLTON TAFT.
Haseltine, Lake & Co.,
45, Southampton Buildings, London, Agents for the Applicant.