1. A step-shaped drill bit comprising at least two stepped cutting edges that are axially provided, wherein
a cutting edge of a first step from a tip is formed so as to satisfy at least one condition selected from the group consisting of:
a number of blades is smaller than that of cutting edges of a second and subsequent step(s), so as to reduce a thrust resistance during a perforation compared with a case in which the first step cutting edge is formed such that the number of blades is the same as that of the second and subsequent step(s),
a point angle of the cutting edge is larger than that of cutting edges of a second and subsequent step(s), so as to reduce a thrust resistance during a perforation compared with a case in which the first step cutting edge is formed such that the point angle of the cutting edge is the same as that of the second and subsequent step(s), and
a clearance angle of the cutting edge is larger than that of cutting edges of a second and subsequent step(s), so as to reduce a thrust resistance during a perforation compared with a case in which the first step cutting edge is formed such that the clearance angle of the cutting edge is the same as that of the second and subsequent step(s).
2. The drill bit as claimed in claim 1 comprising at least three stepped cutting edges that are axially provided, wherein
each of the second and subsequent edges satisfies at least one condition selected from the group consisting of:
having the same or larger number of blades than that of a neighboring edge on the tip side,
having the same or smaller point angle than that of a neighboring edge on the tip side, and
having the same or smaller clearance angle than that of a neighboring edge on the tip side.
3. The drill bit as claimed in claim 1 comprising at least three stepped cutting edges that are axially provided, wherein
each of the second and subsequent edges satisfies at least one condition selected from a group consisting of:
having a larger number of blades than that of a neighboring edge on the tip side,
having a smaller point angle than that of a neighboring edge on the tip side, and
having a smaller clearance angle than that of a neighboring edge on the tip side.
4. The drill bit as claimed in claim 1, wherein an axial distance between a tip of the drill bit and the second edge is the same as or larger than a diameter of the first edge.
5. The drill bit as claimed in claim 1, wherein the first edge is two-bladed.
6. The drill bit as claimed in claim 1, wherein the second edge is four-bladed.
7. The drill bit as claimed in claim 1, comprising a third cutting edge having four blades.
8. The drill bit as claimed in claim 1, wherein
a last edge for finally enlarging a perforated hole has a point angle, at a front end thereof, smaller than a point angle of a front side edge, and
the point angle decreases gradually as a ridge goes to rear end so that the ridge of the last edge forms smoothly curved profile.
9. The drill bit as claimed in claim 8, wherein a point angle of the last edge at a rear end is zero.
10. The drill bit as claimed in claim 9, wherein a diameter of the drill at the position where the point angle is zero is a maximum diameter of the drill bit.
11. The drill bit as claimed in claim 9, wherein a difference of a minimum diameter of the last edge at a front end thereof and a maximum diameter of the last edge at a rear end thereof is not less than 1 mm.
12. The drill bit as claimed in claim 8, wherein the last edge is a third edge of the drill bit.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
What is claimed is:
1. A method of evaluating the adsorption of contaminants on a solid surface, comprising the steps of:
preparing a test piece of a material equal to the material of a workpiece, said test piece being sized to permit said test piece to be housed in an adsorption tube container that is mounted to a mass analyzing apparatus;
leaving said test piece to stand in a measuring site under a test atmosphere for a predetermined time, followed by recovering the test piece and subsequently housing the recovered test piece in said adsorption tube container; and
mounting the adsorption tube container housing said test piece to said mass analyzing apparatus so as to measure the contaminant material and the mass of the contaminant, thereby evaluating the degree of contamination of the measured point.
2. The method of evaluating the adsorption of contaminants on a solid surface according to claim 1, wherein the material of said workpiece is silicon, quartz, glass or a metallic material.
3. The method of evaluating the adsorption of contaminants on a solid surface according to claim 1, wherein said test piece consists of a silicon single plate, and the adsorption tube container housing said test piece is made of silicon, quartz or a glass material.
4. The method of evaluating the adsorption of contaminants on a solid surface according to claim 1, wherein the material of said workpiece is silicon, quartz, glass or a metallic material, said test piece is a silicon single plate, and the adsorption tube container housing said test piece is made of silicon, quartz, or a glass material.