TECHNICAL TIP #26;
DRILLING: PECK FEEDING
Drilling of holes 2 to 3 diameters deep can usually be accomplished with one step. When the need arises to drill 4, 5, or more diameters deep it becomes much more difficult to evacuate chips, especially with non-Coolant hole drills. The deeper the hole the greater the tendency of the chips to becomes jammed in the flutes preventing coolant from reaching the drill tip. This buildup of heat at the drill tip will eventually result in premature failure.
This problem can be overcome by introducing a peck cycle. A peck cycle is where the entire drill is periodically withdrawn from the hole to remove chips, and then re-entering the hole to drill a small distance and withdrawing the drill again until the full hole depth is reached. The first 2 diameters can usually be drilled before initiating a peck drilling cycle. Obviously, peck feeding would not be very efficient for any kind of production work.
The use of coolant hole drills and high-pressure coolant systems will in most cases eliminate the need for peck drilling. Special purpose drills with high spirals and/or parabolic flute forms can also be used to drill deeper holes without peck drilling.
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