Drilling operation (G81 canned cycle) in CNC Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the G81 canned cycle in CNC programming?

G81 is used to automate drilling operations by moving the tool to a specified position, drilling to a set depth, and then retracting, all in one simple command.

beginner

Which parameters are essential in a G81 drilling cycle?

The essential parameters are X and Y for position, Z for drilling depth, R for retract plane, and F for feed rate during drilling.

intermediate

Explain the role of the R parameter in the G81 cycle.

R specifies the retract plane height. It is the position above the workpiece where the tool stops before and after drilling to avoid collisions.

beginner

How does the CNC machine behave after completing a G81 drilling cycle?

After drilling to the specified depth, the tool retracts to the R plane, then moves to the next position or ends the cycle if no more points are given.

intermediate

What happens if the Z parameter is set incorrectly in a G81 cycle?

If Z is too shallow, the hole won't be drilled deep enough; if too deep, it may damage the tool or workpiece by drilling beyond intended depth.

What does the G81 command primarily automate?

A Thread tapping

B Cutting external shapes

C Milling slots

D Drilling holes at specified positions

G81 is specifically designed for drilling holes automatically at given coordinates.

In a G81 cycle, what does the R parameter control?

A Retract height above the workpiece

B Drilling speed

C Tool diameter

D Feed rate

R sets the retract plane height where the tool moves safely above the workpiece.

Which parameter defines how deep the drill goes in a G81 cycle?

A X

B Y

C Z

D F

Z specifies the drilling depth in the G81 canned cycle.

What happens immediately after the drill reaches the Z depth in G81?

A The tool moves to the next hole without retracting

B The tool retracts to the R plane

C The spindle stops

D The feed rate increases

After drilling, the tool retracts to the R plane before moving on.

If you want to drill multiple holes using G81, what must you do?

A Repeat the G81 command with different X and Y positions

B Use G81 only once for all holes

C Change the spindle speed between holes

D Use G80 instead

G81 is modal; invoke it once with parameters, then specify subsequent X Y positions for each hole, and end with G80.

Describe the sequence of movements the CNC machine makes during a G81 drilling cycle.

Think about how the tool approaches, drills, and then moves away.

Explain why setting the R parameter correctly is important in a G81 canned cycle.

Consider what happens if the tool doesn't retract high enough.