Finishing strategies (contour, scallop) in CNC Programming - Step-by-Step Execution

Concept Flow - Finishing strategies (contour, scallop)

Start: Select finishing strategy

↓

Use scallop strategy

Yes↓

Generate contour path

↓

Execute contour machining

↓

Check surface finish

↓

End

This flow shows choosing between contour and scallop finishing, generating paths, and machining to achieve smooth surfaces.

Execution Sample

CNC Programming

G01 X10 Y10 F100 ; Move to start
G01 Z-1 F50 ; Cut down
G01 X50 Y10 ; Contour path
G01 X50 Y50 ; Continue contour
G01 X10 Y50 ; Complete contour
G01 Z5 ; Retract

This CNC code executes a contour finishing pass around a rectangular shape.

Execution Table

Step	G-Code Command	Action	Position (X,Y,Z)	Feed Rate	Result
1	G01 X10 Y10 F100	Feed move to start point	(10,10,0)	100	Positioned at start edge
2	G01 Z-1 F50	Cut down into material	(10,10,-1)	50	Tool engaged at cutting depth
3	G01 X50 Y10	Cut along X axis (contour)	(50,10,-1)	50	Cutting contour edge
4	G01 X50 Y50	Cut along Y axis (contour)	(50,50,-1)	50	Cutting contour edge
5	G01 X10 Y50	Cut back along X axis (contour)	(10,50,-1)	50	Cutting contour edge
6	G01 Z5	Retract tool	(10,50,5)	50	Tool safely above workpiece
7	End	-	-	-	Contour finishing complete

💡 All contour edges cut, tool retracted, finishing pass complete

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	Final
Position	(0,0,0)	(10,10,0)	(10,10,-1)	(50,10,-1)	(50,50,-1)	(10,50,-1)	(10,50,5)	(10,50,5)
Feed Rate	0	100	50	50	50	50	50	50
Tool State	Up	Up	Down	Down	Down	Down	Up	Up

Key Moments - 3 Insights

Why does the tool retract (Z moves up) at the end of the contour pass?

The tool retracts to move safely above the workpiece to avoid collisions when moving to the next position or finishing the program, as shown in step 6 of the execution_table.

Why is the feed rate slower when cutting compared to moving to start position?

Feed rate is slower during cutting (50) to control the tool and avoid damage, while moving to start (100) is faster since the tool is not cutting, as seen in steps 1 and 2.

What is the difference between contour and scallop finishing in terms of tool path?

Contour finishing follows the exact edge shape (like the rectangle here), while scallop finishing moves in overlapping arcs to smooth surfaces. This example shows contour path generation.

Visual Quiz - 3 Questions

Look at the execution_table, what is the tool position after step 3?

A (50,10,-1)

B (10,10,-1)

C (50,50,-1)

D (10,50,-1)

💡 Hint

Check the Position column in row for step 3 in execution_table

At which step does the tool start cutting into the material?

A Step 1

B Step 4

C Step 2

D Step 6

💡 Hint

Look for Z coordinate change from 0 to negative in execution_table

If feed rate during cutting was increased to 100, what would change in the execution_table?

A Position values would change

B Feed Rate column would show 100 for steps 2 to 5

C Tool would not retract

D No change at all

💡 Hint

Feed Rate column shows speed; changing feed rate affects this value, not position or tool state

Concept Snapshot

Finishing strategies guide the final tool path for smooth surfaces.
Contour follows exact edges; scallop moves in overlapping arcs.
Use G01 moves with controlled feed rates for cutting.
Retract tool after finishing to avoid collisions.
Feed rate is slower during cutting than rapid moves.
Choose strategy based on surface shape and finish quality.

Full Transcript

This visual execution shows how a CNC finishing strategy using contour works step-by-step. The program moves the tool to the start position quickly, then lowers it to cutting depth. It follows the rectangular contour edges with controlled feed rate to cut smoothly. After completing the contour, the tool retracts safely above the workpiece. Variables like position, feed rate, and tool state change at each step. Key moments include why the tool retracts, why feed rate changes, and the difference between contour and scallop finishing. The quiz tests understanding of tool position, cutting start, and feed rate effects. This helps beginners see how finishing strategies run in CNC programming.