Pecking Order – Subprogramming on a CNC Lathe

Drilling holes can be tough work. Problems with chip control, poor tool life and coolant starvation are but a few of the holemaking obstacles machinists face every day. To make things even harder, controls sometime present another hurdle that must be overcome: programming.

Fanuc and Fanuc-compatible controls offer many programming features that make life easier. But sometimes pecking cycles aren’t present or don’t work as desired.

Assume for a minute that you need to make a part with a 1/4″-dia., 2″-deep hole. It’s the programmer’s day off, so you find yourself standing in front of a CNC lathe, scratching your head. Where do you begin? If your machine uses G and M codes, you could program the following:

N1 G97 M3 S1000 T101
G0 X0 Z.1
G1 Z-2. F.005
G0 Z.3
G28 U0 W0
M30

This bare-bones program will start the spindle at 1,000 rpm, index the turret to tool station 1, then rapid to the centerline of the part and start drilling.

Now, if you’re drilling Styrofoam, this program would work fine. But if you’re drilling a real-world material like steel or aluminum, your drill will probably snap off somewhere deep in the workpiece. Drilling holes that are more than 4 or 5 diameters deep usually requires pecking—a periodic retraction of the drill. Pecking clears the chip and allows cutting fluid to enter the hole.

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