Approach and retract moves in CNC Programming - Step-by-Step Execution

Concept Flow - Approach and retract moves

Start at safe position

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Approach move: move tool close to workpiece

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Perform machining operation

↓

Retract move: move tool away from workpiece

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Return to safe position or next step

The tool starts safely away, moves close to the workpiece (approach), performs machining, then moves away (retract) to avoid collisions.

Execution Sample

CNC Programming

G00 Z5.0 ; Retract to safe height
G01 X10 Y10 Z-1.0 F100 ; Approach and cut
G00 Z5.0 ; Retract after cut

Moves tool up to safe height, then approaches workpiece to cut, then retracts back up.

Execution Table

Step	Command	Position (X,Y,Z)	Feed Rate	Action
1	G00 Z5.0	(current X, current Y, 5.0)	Rapid	Retract to safe height
2	G01 X10 Y10 Z-1.0 F100	(10, 10, -1.0)	100	Approach and cut at workpiece
3	G00 Z5.0	(10, 10, 5.0)	Rapid	Retract after cut

💡 Program ends after retracting to safe height at step 3

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3
X	current	current	10	10
Y	current	current	10	10
Z	current	5.0	-1.0	5.0
Feed Rate	N/A	Rapid	100	Rapid

Key Moments - 3 Insights

Why do we move the tool up to Z5.0 before and after cutting?

Moving to Z5.0 is a retract move to keep the tool safely away from the workpiece and avoid collisions, as shown in steps 1 and 3 of the execution_table.

What is the difference between G00 and G01 commands here?

G00 is a rapid move used for quick positioning without cutting (steps 1 and 3), while G01 is a controlled feed move used for cutting (step 2), as seen in the execution_table.

Why do we specify feed rate only in the approach move?

Feed rate controls cutting speed and is needed only during machining moves like step 2; rapid moves (steps 1 and 3) do not require feed rate.

Visual Quiz - 3 Questions

Look at the execution_table, what is the Z position after step 2?

A -1.0

B 5.0

C 0.0

D 10.0

💡 Hint

Check the Position column in row for step 2 in execution_table.

At which step does the tool perform the cutting operation?

A Step 1

B Step 2

C Step 3

D None

💡 Hint

Look at the Action column in execution_table for the cutting move.

If the retract height changed from Z5.0 to Z10.0, what would change in the variable_tracker after step 1?

A X would change to 10

B Feed Rate would change to 100

C Z would be 10.0 instead of 5.0

D Y would change to 5.0

💡 Hint

Check the Z variable values after step 1 in variable_tracker.

Concept Snapshot

Approach and retract moves:
- Retract moves (G00) move tool safely away (e.g., Z5.0)
- Approach moves (G01) move tool close to workpiece for cutting
- Feed rate applies only during cutting moves
- Retract after cutting to avoid collisions
- Always start and end at safe positions

Full Transcript

This lesson shows how CNC tools move safely before and after cutting. First, the tool retracts up to a safe height (Z5.0) using a rapid move (G00). Then it approaches the workpiece at controlled speed (G01) to cut at position X10 Y10 Z-1.0 with feed rate 100. After cutting, it retracts back up to Z5.0 rapidly to avoid hitting the workpiece. Variables X, Y, Z, and feed rate change step by step. Retract moves keep the tool safe, approach moves perform cutting, and feed rate is only needed during cutting. Understanding these moves prevents crashes and ensures smooth machining.