Finishing strategies (contour, scallop) in CNC Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of a contour finishing path command

What is the expected toolpath output for this contour finishing G-code snippet?

CNC Programming

G01 X10 Y10 F100
G01 X20 Y10
G01 X20 Y20
G01 X10 Y20
G01 X10 Y10

A A square path starting at (10,10) moving clockwise

B A circular path around the points

C A diagonal line from (10,10) to (20,20)

D A square path starting at (10,10) moving counterclockwise

💡 Hint

Contour finishing follows the shape edges in a closed loop.

The G01 commands move the tool in straight lines forming a square path starting at (10,10) and moving clockwise.

🧠 Conceptual

intermediate

Difference between contour and scallop finishing

Which statement best describes the difference between contour and scallop finishing strategies?

A Both contour and scallop finishing remove material in straight lines only.

B Scallop finishing follows the shape edges; contour finishing removes material in arcs.

C Contour finishing is used only for roughing; scallop finishing is for drilling.

D Contour finishing follows the exact shape edges; scallop finishing removes material in overlapping arcs.

💡 Hint

Think about how the tool moves relative to the shape edges.

Contour finishing traces the exact edges of the part, while scallop finishing uses overlapping arcs to smooth surfaces.

🔧 Debug

advanced

Identify the error in this scallop finishing G-code snippet

What error will this scallop finishing G-code cause when executed?

CNC Programming

G02 X30 Y30 I5 J0 F150
G02 X40 Y30 I5 J0
G02 X40 Y40 I0 J5
G02 X30 Y40 I0 J5

A Syntax error due to missing feed rate on second line

B Runtime error because arcs do not connect smoothly

C No error; code runs correctly producing scallop arcs

D Tool will move in straight lines instead of arcs

💡 Hint

Check if the arcs connect properly at endpoints.

The arcs defined do not connect smoothly, causing a runtime error or unexpected toolpath.

🚀 Application

advanced

Calculate scallop height for a given tool and step-over

Given a ball-end mill with radius 5mm and a scallop step-over of 4mm, what is the approximate scallop height?

A 0.2 mm

B 0.5 mm

C 0.4 mm

D 1.0 mm

💡 Hint

Use the formula h = r - sqrt(r^2 - (s/2)^2), where r is radius and s is step-over.

Plugging in r=5 and s=4 gives h ≈ 0.4 mm scallop height.

📝 Syntax

expert

Identify the correct G-code snippet for contour finishing with a clockwise path

Which G-code snippet correctly programs a contour finishing path moving clockwise around a rectangle from (0,0) to (50,30)?

A

G01 X0 Y0
G01 X50 Y0
G01 X50 Y30
G01 X0 Y30
G01 X0 Y0

B

G01 X0 Y0
G01 X0 Y30
G01 X50 Y30
G01 X50 Y0
G01 X0 Y0

C

G01 X0 Y0
G01 X50 Y30
G01 X50 Y0
G01 X0 Y30
G01 X0 Y0

D

G01 X0 Y0
G01 X50 Y0
G01 X0 Y30
G01 X50 Y30
G01 X0 Y0

💡 Hint

Clockwise movement around a rectangle starts at bottom-left, moves right, then up, then left, then down.

Option A moves from (0,0) right to (50,0), up to (50,30), left to (0,30), then down to (0,0), which is clockwise.