Arc programming with R (radius) in CNC Programming - Step-by-Step Execution

Concept Flow - Arc programming with R (radius)

Start Arc Command

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Specify Start Point

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Specify End Point

↓

Specify Radius (R)

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Calculate Arc Path

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Execute Arc Movement

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End Arc Command

The CNC arc command starts by defining start and end points, then uses the radius R to calculate the arc path before executing the movement.

Execution Sample

CNC Programming

G02 X10 Y10 R5

This code commands a clockwise arc move to X=10, Y=10 with a radius of 5 units.

Execution Table

Step	Command Part	Value	Action	Result
1	G-code	G02	Select clockwise arc move	Arc mode set to clockwise
2	X	10	Set end X coordinate	End point X=10
3	Y	10	Set end Y coordinate	End point Y=10
4	R	5	Set radius	Radius set to 5 units
5	Calculate	Arc path	Compute arc center and path	Arc path calculated based on radius and points
6	Execute	Move	Move tool along arc	Tool moves clockwise along arc to (10,10)
7	End		Arc command complete	Arc move finished

💡 Arc move completes after tool reaches end point (10,10) along the arc with radius 5

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
End X	undefined	10	10	10	10
End Y	undefined	undefined	10	10	10
Radius R	undefined	undefined	undefined	5	5
Arc Mode	undefined	clockwise	clockwise	clockwise	clockwise

Key Moments - 2 Insights

Why do we specify only the radius R and not the center coordinates in the arc command?

The CNC controller calculates the arc center automatically from the start point, end point, and radius R, as shown in step 5 of the execution_table.

What happens if the radius R is too small or too large for the given start and end points?

The controller will give an error or adjust the arc path because the radius must fit the distance between points; this is implied in step 5 where arc path calculation occurs.

Visual Quiz - 3 Questions

Look at the execution_table, what is the radius value after step 4?

A 10

B undefined

C 5

D 15

💡 Hint

Check the 'Radius R' variable in variable_tracker after step 4.

At which step does the CNC controller calculate the arc path?

A Step 5

B Step 3

C Step 6

D Step 2

💡 Hint

Refer to the 'Calculate' action in the execution_table.

If the command was G03 instead of G02, what would change in the execution_table?

A End point coordinates would change

B Arc mode would be counterclockwise instead of clockwise

C Radius R would be ignored

D No arc would be executed

💡 Hint

Look at step 1 where arc mode is set based on G-code.

Concept Snapshot

Arc programming with R uses G02/G03 commands.
Specify end point (X,Y) and radius (R).
Controller calculates arc center automatically.
G02 = clockwise arc, G03 = counterclockwise.
Radius must fit between start and end points.
Arc moves tool along curved path smoothly.

Full Transcript

Arc programming with radius R in CNC uses commands like G02 for clockwise arcs. The program specifies the end point coordinates X and Y, and the radius R. The CNC controller calculates the arc center automatically from these inputs. The execution flow starts by selecting the arc mode, setting end coordinates, setting the radius, calculating the arc path, and then moving the tool along the arc. The radius value is stored and used to compute the arc path. The arc completes when the tool reaches the end point along the curved path. If the radius is not suitable, the controller will raise an error during calculation. Changing G02 to G03 changes the arc direction to counterclockwise. This method simplifies programming arcs without manually calculating center points.

Practice

1. Which G-code command is used to program a clockwise arc with a specified radius using R?

easy

A. G02

B. G03

C. G01

D. G00

Solution

1. Step 1: Understand G-code commands for arcs

   G02 is used for clockwise arcs, while G03 is for counterclockwise arcs.

2. Step 2: Identify the command for clockwise arc with radius

   Since the question asks for clockwise arc with radius, G02 is the correct command.

3. Final Answer:

   G02 -> Option A

4. Quick Check:

   Clockwise arc = G02 [OK]

Hint: Clockwise arcs always use G02 command [OK]

Common Mistakes:

• Confusing G02 with G03 for arc direction
• Using G01 which is for straight lines
• Using G00 which is for rapid moves

2. Which of the following is the correct syntax to program a counterclockwise arc ending at X10 Y20 with radius 5?

easy

A. G01 X10 Y20 R5

B. G03 X10 Y20 R5

C. G03 X10 Y20 I5

D. G02 X10 Y20 R5

Solution

1. Step 1: Identify the command for counterclockwise arc

   G03 is used for counterclockwise arcs.

2. Step 2: Check the syntax for arc with radius

   Using R specifies the radius; X and Y specify the end point.

3. Final Answer:

   G03 X10 Y20 R5 -> Option B

4. Quick Check:

   Counterclockwise arc with radius uses G03 and R [OK]

Hint: Use G03 with R for counterclockwise arc radius [OK]

Common Mistakes:

• Using G02 instead of G03 for counterclockwise
• Using I instead of R for radius
• Using G01 which is for straight moves

3. What will be the end position after executing the command G02 X15 Y10 R5 starting from X10 Y10?

medium

A. Ends at X10 Y15 following a clockwise arc with radius 5

B. Ends at X15 Y10 following a straight line

C. Ends at X15 Y10 following a clockwise arc with radius 5

D. Syntax error due to missing I and J

Solution

1. Step 1: Understand the command components

   G02 means clockwise arc; X15 Y10 is the end point; R5 is the radius.

2. Step 2: Confirm the movement

   The tool moves from X10 Y10 to X15 Y10 along a clockwise arc with radius 5.

3. Final Answer:

   Ends at X15 Y10 following a clockwise arc with radius 5 -> Option C

4. Quick Check:

   G02 with R moves on arc to specified X,Y [OK]

Hint: R defines arc radius; X,Y is arc end point [OK]

Common Mistakes:

• Thinking it moves in a straight line
• Confusing arc direction
• Assuming I and J are always required

4. Identify the error in the following CNC arc command: G03 X20 Y30 R-10

medium

A. Negative radius value is invalid

B. Missing I and J parameters

C. G03 cannot be used with R parameter

D. X and Y coordinates are out of range

Solution

1. Step 1: Check the radius value

   Radius (R) must be positive; negative radius is not valid in arc programming.

2. Step 2: Verify other parameters

   G03 supports R parameter; I and J are optional when R is used; X and Y are valid coordinates.

3. Final Answer:

   Negative radius value is invalid -> Option A

4. Quick Check:

   Radius must be positive [OK]

Hint: Radius R must always be positive [OK]

Common Mistakes:

• Using negative radius values
• Assuming I and J are mandatory with R
• Thinking G03 disallows R parameter

5. You want to program a clockwise arc from X0 Y0 to X10 Y0 with radius 10. Which command correctly achieves this?

hard

A. G03 X10 Y0 R10

B. G02 X10 Y0 R-10

C. G01 X10 Y0 R10

D. G02 X10 Y0 R10

Solution

1. Step 1: Determine arc direction and parameters

   Clockwise arc uses G02; end point is X10 Y0; radius is positive 10.

2. Step 2: Validate command correctness

   G02 with X10 Y0 R10 correctly programs the clockwise arc; negative radius is invalid; G03 is counterclockwise; G01 is linear move.

3. Final Answer:

   G02 X10 Y0 R10 -> Option D

4. Quick Check:

   Clockwise arc with positive radius uses G02 [OK]

Hint: Clockwise arc = G02 with positive R [OK]

Common Mistakes:

• Using negative radius
• Confusing G02 and G03
• Using G01 which is not an arc command