Process Characteristics of Centering Drill
December 28,2022
Before drilling, use a rigid centering drill to drill an initial hole with a depth of 1~2 times the diameter to ensure the accuracy of drilling with a common drill, and reserve a chamfer for tapping to facilitate tapping.
What are the process characteristics of the centering drill?
Chamfer hole
It can also be used to process the chamfered hole before formal drilling. By controlling the drilling depth of the centering drill, the required chamfer hole diameter can be formed while determining the hole location. You can process a centering hole for the second drilling in the same step, and form a chamfer at the hole mouth at the same time. A small increase in the centering drilling depth will result in a larger hole diameter than the secondary drill. In this way, when you drill with a small diameter secondary drill, you can obtain a chamfer with a larger diameter at the orifice.
Drill point angle
The drill point angle of the second bit is usually 118 °, 120 °, or 135 °. Some bits with higher strength requirements will use a larger drill point angle. Some people use a 145° centering drill to drill the centering hole for a secondary drill with a 135° angle. When processing some work-piece materials with good toughness, the second drill bit is more likely to be damaged. So it is essential to use a 145 ° centering drill.
The other way is that both the centering drill and the secondary drill use the same drill tip angle. In this way, the drill point and cutting edge of the second drill will cut into the workpiece at the same time. This may cause chatter due to the same cut-in angle, and chatter may cause the secondary bit to break.
Whether the cutting speed and feed rate are appropriate depends on the requirements of the workpiece material, blade substrate, and coating, as well as the drilling itself. Generally speaking, the cutting speed and feed rate of centering drilling should be lower than that of secondary drilling. The purpose of centering drilling is to provide a correct initial hole position for secondary drilling. So it is unnecessary to achieve a high drilling rate.