Pocket milling (rectangular) in CNC Programming - Step-by-Step Execution

Concept Flow - Pocket milling (rectangular)

Start at initial corner

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Move tool to start position

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Mill along X axis to opposite corner

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Step over in Y axis

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Mill back along X axis

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Repeat stepping and milling until pocket is done

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Retract tool and end

The tool moves back and forth along the X axis, stepping over in Y after each pass, to clear a rectangular pocket area.

Execution Sample

CNC Programming

G0 X0 Y0 Z5
G1 Z-2 F100
G1 X50 Y0 F200
G1 X50 Y10
G1 X0 Y10
G1 X0 Y20
G1 X50 Y20
G0 Z5

This CNC code mills a rectangular pocket by moving the tool in straight lines along X and Y axes with step overs.

Execution Table

Step	Command	Tool Position (X,Y,Z)	Action	Output/Result
1	G0 X0 Y0 Z5	(0,0,5)	Rapid move to start above material	Tool above start corner
2	G1 Z-2 F100	(0,0,-2)	Plunge into material	Tool at cutting depth
3	G1 X50 Y0 F200	(50,0,-2)	Mill along X axis to right edge	Material removed along bottom edge
4	G1 X50 Y10	(50,10,-2)	Step over in Y axis	Tool moves up to next pass line
5	G1 X0 Y10	(0,10,-2)	Mill back along X axis	Material removed along next pass
6	G1 X0 Y20	(0,20,-2)	Step over in Y axis	Tool moves up again
7	G1 X50 Y20	(50,20,-2)	Mill along X axis	Material removed along top pass
8	G0 Z5	(50,20,5)	Retract tool	Tool lifted out of pocket
9	End	(50,20,5)	Pocket milling complete	Rectangular pocket cleared

💡 Tool retracts after completing all passes to clear the rectangular pocket.

Variable Tracker

Variable	Start	After Step 3	After Step 5	After Step 7	Final
X	0	50	0	50	50
Y	0	0	10	20	20
Z	5	-2	-2	-2	5

Key Moments - 3 Insights

Why does the tool move back along the X axis after stepping over in Y?

Because the tool mills the pocket in a zigzag pattern, moving forward along X, stepping over in Y, then moving back along X to cover the entire rectangular area (see steps 3,4,5).

Why is the Z axis lowered only once at the start and not during each pass?

The tool plunges to the cutting depth once at the start (step 2) and stays there while moving in X and Y to mill the pocket, avoiding unnecessary up/down moves (see steps 2-7).

What happens if the step over in Y is too large?

If the step over is too large, some material will be left uncut between passes, resulting in an incomplete pocket (refer to step 4 and 6 for step over moves).

Visual Quiz - 3 Questions

Look at the execution table, what is the tool position after step 5?

A (0,10,-2)

B (50,10,-2)

C (50,0,-2)

D (0,0,-2)

💡 Hint

Check the 'Tool Position' column for step 5 in the execution_table.

At which step does the tool retract out of the pocket?

A Step 7

B Step 6

C Step 8

D Step 9

💡 Hint

Look for the command that moves Z back to 5 in the execution_table.

If the step over in Y was doubled, how would the execution_table change?

A More X axis moves per pass

B Fewer Y step over steps, fewer passes

C More Z plunges per pass

D No change in passes

💡 Hint

Step over in Y controls how many passes are needed to cover the pocket height (see steps 4 and 6).

Concept Snapshot

Pocket milling (rectangular):
- Tool moves in zigzag along X axis
- Steps over in Y after each pass
- Plunges once to cutting depth
- Retracts after all passes
- Step over size controls finish quality

Full Transcript

Pocket milling for a rectangular area involves moving the cutting tool back and forth along the X axis while stepping over in the Y axis after each pass. The tool starts above the material, plunges to the cutting depth once, then mills along the X axis to the opposite edge. It steps over in Y, mills back along X, and repeats until the entire rectangular pocket is cleared. Finally, the tool retracts out of the pocket. This zigzag pattern ensures efficient material removal. The step over distance in Y affects how well the pocket is cleared without leaving uncut material. The execution table shows each step with tool position and action, helping visualize the process clearly.