Masonry drill bit

Details Masonry drill bit Masonry drill bit

2000-07-17

2001-12-11

Howell, Daniel W. (Department: 3722)

Cutting by use of rotating axially moving tool

Tool or tool with support

Having stepped cutting edges

C175S389000, C175S395000, C175S415000, C175S420100, C408S230000

Reexamination Certificate

active

06328506

ABSTRACT:

This invention relates to masonry drill bits, and in particular to a masonry drill bit which is usable with rotary and percussion drills and electro-pneumatic hammers.
In known masonry drill bits, a hard metal or carbide tip providing edges for drilling concrete, brick, natural stone or the like is brazed into an end of a drill bit shaft. The shaft is usually a helically twisted steel web having a shank at its free end for insertion into the chuck or tool holder of a drill or hammer. The cutting edges of the drill bit tip usually extend in a straight uninterrupted line from the forward extremity of the drill bit to the outer diameter of the drill bit. These cutting edges also usually extend slightly rearwardly from the centre to the outside of the drill bit.
GB-1270347 discloses a masonry drill bit which includes a pilot tip in the form a forward extension of the drill bit tip. This pilot tip is included to guide the drill bit into a workpiece and to assist in preventing the drill bit from being forced off-line when the drill bit strikes a stone or pebble in the masonry being drilled.
Although it is important for a masonry drill bit to produce a hole in a workpiece as quickly as possible, market research has indicated that the life of the drill bit and a reduction in edge chipping of the hole are considered by consumers to be far more important than a saving in the time needed to drill a hole with the drill bit. With this in mind, the present applicant has developed a novel masonry drill bit which is efficient at cutting holes in workpieces and, in general, has a longer life than equivalent drill bits currently on the market.
In accordance with the foregoing, the present invention provides a masonry drill bit having an active diameter of D, comprising a shaft and a tip for engaging a workpiece, the tip including a central portion extending ahead of an outer portion, wherein the central portion has a width of at least 0.25D and is shaped to act as a chisel during percussion drilling, and wherein the outer portion is shaped to cut a workpiece as the drill bit rotates.
By including the central portion, which has a significant width compared to the total active diameter of the drill bit, a substantial chiselling action is produced, during use, by the drill bit as the drill bit is reciprocated by a percussion drill or hammer. Furthermore, by providing a stout central portion, failure of the drill bit is less likely to occur.
Preferably the width of the central portion is between 0.25D and 0.75D. The particular relative width of the central portion is dictated by the actual active diameter of the masonry drill bit. For example, if the active diameter is small, such as 4 mm, the relative width of the central portion is preferably high, such as 0.75D. If, however, the active diameter of the drill bit is large, such as 20 mm, the relative width of the central portion is preferably smaller, such as about 0.33D. This is because, if the relative width of the central portion is large for a drill bit having a large active diameter, the edge of the hole produced by the drill bit may become chipped or otherwise damaged during drilling.
The central portion preferably includes a central chisel edge defined by two pairs of flanks inclined away from the chisel edge. By including a flank on the leading edges of the central portion, such that the central portion has negative leading edges, failure of the drill bit tip is less likely to occur.


REFERENCES:
patent: 2879036 (1959-03-01), Wheeler
patent: 3199381 (1965-08-01), Mackey
patent: 4568227 (1986-02-01), Hogg
patent: 6102634 (2000-08-01), Turner et al.

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