FROM: Precision Twist Drill Co.

DATE: February, 1997

When drilling deep holes with pressurized coolant hole drills, it is critical to remember the basic principles of successful hole-making. These principles fall into three categories:

. FORMING A CHIP

. MANAGING A CHIP

. EVACUATING THE CHIP

Let’s look more closely at each of the categories.

FORMING A CHIP...

Chip formation is extremely important when drilling deep holes. because of the limited space in a drill flute, it is best to have chips broken into small pieces. Long “stringers” and coiled chips tend to pack in the flutes and can cause a drill to break.

Two factors affect the formation of chips.

.The ductility of the material, that is, the material’s malleability or pliability

.The feed per revolution

MANAGING THE CHIP...

Ductile materials tend to coil during drilling. this coiling can be controlled by changing the rake angles or by introducing chip breakers to the point. probably the most common method of chip control is changing the rake angle on the lips. With a decreased rale, the chip bends more sharply. This causes the chip to break instead of curl.

The other method of chip management is to grind chip breaker grooves into the cutting lips. Either method requires great care, and remember that both methods can reduce the drill’s life.

EVACUATING THE CHIP...

Chip evacuation is largely dependent on whether the application involves vertical or horizontal drilling. In conjunction with this, consideration needs to be given to the amount of coolant pressure available. The combination of these elements -- vertical or horizontal applications and coolant pressure -- will influence the selected helix angle appropriate for the application.

For Vertical Applications...

When drilling in a vertical application with low coolant pressure, a higher or faster helix angle is usually required to help evacuate the chip. When higher coolant pressures are available (500-1,000 psi) the helix becomes less important. This is because the pressure has a tendency to blow the chips out of the flutes.

For Horizontal Applications....

When drilling in a horizontal position and coolant pressure is low (50 psi or less), it is best to use a low or slow helix drill. Slow helix drills provide a straighter path for chip removal. Again, when coolant pressure is high, helix angle id less of an issue.

In both vertical and horizontal applications, it is better to have higher coolant pressures. Coolant pressure not only aids in the removal of chips, it helps in keeping the drill point cool. This has the likely result of increasing tool life.

If you have special applications or need assistance, our tool engineers are available to help.

---

PRECISION TWIST DRILL CO.