Cutting by use of rotating axially moving tool – Tool or tool with support – Having peripherally spaced cutting edges
Patent
1994-08-04
1997-01-07
Howell, Daniel W.
Cutting by use of rotating axially moving tool
Tool or tool with support
Having peripherally spaced cutting edges
408227, B23B 5102
Patent
active
055909876
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a precision twist drill bit.
Drill bits are well known and have been used for a very long time for drilling cylindrical holes. It is known that, going from the top to the bottom, a drill bit has a point which centers the tool and which is extended by two blades, each of which is edged by a lip, the blades being separated by two flutes which extend helically towards the bottom of the drill bit and which receive the swarf of the cut metal and remove it, in general upwards. At the point, the blades of the drill define a first clearance, the lands of the drill form a second clearance.
Unfortunately, the precision obtained in such drilling is about one-tenth of a millimeter, and when a determined higher precision is required, or when a good quality surface state is essential, a subsequent reaming operation must be performed to improve the hole drilled by the drill bit. In other words, an initial hole is drilled, and that hole is then usually reamed by using the tool or a reamer to obtain the final quality (H7-H8). When there are a large number of holes to be drilled, the resulting lost time adds to the production costs.
An object of the present invention is to mitigate that drawback, and to provide a tool enabling drilling to be performed directly without any re-working or any burrs, and to a tolerance of not more than 0.03 millimeters with a surface state of less then 0.8 microns Ra. This result is obtained by strictly defining the geometrical shape and the surface state of the tool.
The precision drill bit of the present invention is characterized in that: plus 5 thousandths of a millimeter; depression which extends into the first and second clearances as well as the flute thereby forming a cutting edge. center of the tool; and less than 0.1 microns Ra.
By determining this set of parameters, it is possible to obtain the desired result when they are simultaneously present.
By polishing the surfaces of the flutes, of the depression and lips, it is easier to remove the swarf which then does not degrade the inside surface of the hole.
Naturally, the tool may be made of rapid-machining steel or of any other material that is commonly used for drilling holes, such as tungsten carbide, ceramic, etc.
Other characteristics and advantages of the invention will appear on reading the following description of a particular embodiment given by way of non-limiting example, and with reference to the accompanying drawing, in which:
FIG. 1 shows a drill bit of the invention seen from the front;
FIG. 2 shows the front of the drill bit seen looking in direction II of FIG. 1;
FIG. 3 shows the front of the drill bit seen looking in direction III of FIG. 1; and
FIG. 4 shows the front of the drill bit seen looking in direction IV of FIG. 1.
The figures show that the point of the drill bit includes two blades formed with lips 1 and 2, the blades being ground to a point angle. The blades of the drill define a first clearance 3, and the lands of the drill 7 define a second clearance.
In accordance with one of the characteristics of the invention, the width of the first clearance is very small, and is in the approximate range 0.1 mm to 0.2 mm. The point of the drill bit is formed with two depression 4 which are gymmetrical with respect to one another about the axis of the drill bit. Each depression is basically spherical in shape extending into the first and second clearances as well as the flute of the drill bit thereby defining a basically circular edge. As shown in FIG. 1, each depression forms a cutting edge at the intersection of the depression and the lip formed in the blade. About one-third circular edge is a cutting edge is formed in the first clearance and two-thirds of the circular edge is formed in the second clearance and flute.
The cutting edges of the two depressions 4 must be symmetrical about the center of the tool, with constant thickness as a reference. The point of the tool must be exactly in the center of the tool.
As represented by the arrows F on FIG. 2, the front portions 6 of the bl
REFERENCES:
patent: 1467491 (1923-09-01), Oliver
patent: 2936658 (1960-05-01), Riley
patent: 4116580 (1978-09-01), Hall et al.
patent: 5141369 (1992-08-01), Palace
Tool and Manufacturing Engineers Handbook, vol. 1, Machining, Society of Manufacturing Engineers, 1983, Chapter 9, pp. 14-15.
Etablissements Recoules et Fils (S.A.)
Howell Daniel W.
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