
Center Drills are the tool for making center hole. Center Drills are also used for positioning before drilling, and for chamfering of the hole. ■Table of recommend centering condition.
Work Soft structural steels Carbon steels Alloy steels Stainless steels Aluminum alloy casting
■Names of each part Shank portion Countersink portion material
Drill diam. (Dc) Drill portion Cutting speed
Diameter Revolution Speed Feed per revolution Revolution Speed Feed per revolution Revolution Speed Feed per revolution Revolution Speed Feed per revolution Revolution Speed Feed per revolution (Ds) Drill length (ℓ) Overall length (L)
Type A (60°) Center hole & 60°center Type B (60°) Center hole & 60°center Type A (90°) Center hole & 90°center
Type R Center hole & 60°center
Work Soft structural steels Carbon steels Alloy steels Thermal refined steels Stainless steels Aluminum alloy casting
material Cutting speed Diameter Revolution Speed Feed per revolution Revolution Speed Feed per revolution Revolution Speed Feed per revolution Revolution Speed Feed per revolution Revolution Speed Feed per revolution Revolution Speed Feed per revolution
Avoid scar or distortion resulting from a blow
Note : Advantage of Type B center holes : B type center drill protect the 60° conical bearing surface from scar or distortion resulting from a blow, roughness of workpiece surface or burrs around the hole. Carbide+TiAIN (C-PE-Q-V PE-90˚)
| Work | Soft structural steels | Carbon steels | Alloy steels | Thermal refined steels | Stainless steels | Aluminum alloy casting | ||
| ■Advantage of Type R Center holes | material | |||||||
| Cutting speed |
Angle of center hole is higher than Angle of center hole is lower than Center hole and center are misaligned.
that of center. that of center. Diameter Revolution Speed Feed per revolution Revolution Speed Feed per revolution Revolution Speed Feed per revolution Revolution Speed Feed per revolution Revolution Speed Feed per revolution Revolution Speed Feed per revolution
A type
R type
Technical Inf Note : R type center hole stably holds the center. It also some of advantage of B type center hole.
1. Above condition done by Water Soluble oil. 2. 20% lower feed is recommended when centering process to inclined plane. 3. 20% lower feed is recommended in the case of long shank point drills.