Rest machining for remaining material in CNC Programming - Step-by-Step Execution

Concept Flow - Rest machining for remaining material

Start rough machining

↓

Remove most material

↓

Check remaining material

↓

If remaining material > threshold?

No→Finish machining

Yes↓

Perform rest machining

↓

Finish machining

The process starts with rough machining to remove most material, then checks for leftover material. If leftover is above a set limit, rest machining removes it before finishing.

Execution Sample

CNC Programming

G90 G54
Milling rough pass
Check leftover material
If leftover > 0.5mm
  Perform rest machining
End

This CNC program rough machines the part, checks leftover material, and performs rest machining if leftover is more than 0.5mm.

Execution Table

Step	Action	Remaining Material (mm)	Condition	Next Action
1	Start rough machining	10.0	N/A	Remove material
2	After rough pass	0.8	0.8 > 0.5	Perform rest machining
3	Rest machining pass	0.3	0.3 > 0.5	No, finish machining
4	Finish machining	0.3	N/A	End program

💡 Remaining material 0.3mm is less than threshold 0.5mm, so machining finishes.

Variable Tracker

Variable	Start	After Rough Pass	After Rest Pass	Final
Remaining Material (mm)	10.0	0.8	0.3	0.3

Key Moments - 2 Insights

Why do we check the remaining material after rough machining?

Because rough machining removes most material but leaves some behind; checking ensures rest machining only runs if leftover is significant, as shown in execution_table step 2.

What happens if the remaining material is less than the threshold?

The program skips rest machining and finishes, as seen in execution_table step 3 where 0.3mm < 0.5mm.

Visual Quiz - 3 Questions

Look at the execution table, what is the remaining material after the rough pass?

A 10.0 mm

B 0.8 mm

C 0.3 mm

D 0.5 mm

💡 Hint

Check the 'Remaining Material' column at step 2 in the execution_table.

At which step does the program decide to perform rest machining?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look at the 'Condition' and 'Next Action' columns in execution_table step 2.

If the leftover threshold changed to 0.2 mm, what would happen at step 3?

A Program would restart rough machining

B Machining would finish

C Rest machining would run again

D Program would stop with error

💡 Hint

Compare leftover 0.3 mm with new threshold 0.2 mm in execution_table step 3.

Concept Snapshot

Rest machining removes leftover material after rough machining.
Check leftover material after rough pass.
If leftover > threshold, run rest machining.
Otherwise, finish machining.
This ensures precision and efficiency.

Full Transcript

Rest machining for remaining material starts with rough machining to remove most of the stock. After rough machining, the program checks how much material is left. If the leftover material is more than a set threshold, rest machining is performed to clean up the remaining material. If leftover is less than the threshold, machining finishes. This process ensures the part is machined precisely without unnecessary passes. The execution table shows leftover material starting at 10 mm, reduced to 0.8 mm after rough machining, which triggers rest machining. After rest machining, leftover is 0.3 mm, less than the 0.5 mm threshold, so machining ends.

Practice

1. What is the main purpose of rest machining in CNC programming?

easy

A. To remove leftover material after rough machining

B. To perform the initial rough cut on the raw material

C. To polish the surface after finishing

D. To drill holes in the workpiece

Solution

1. Step 1: Understand rest machining concept

   Rest machining focuses on removing leftover material that rough machining did not clear.

2. Step 2: Differentiate from other machining steps

   Rough machining removes bulk material; rest machining cleans remaining parts for better finish.

3. Final Answer:

   To remove leftover material after rough machining -> Option A

4. Quick Check:

   Rest machining = leftover removal [OK]

Hint: Rest machining targets leftover material after rough cuts [OK]

Common Mistakes:

• Confusing rest machining with rough machining
• Thinking rest machining is for polishing
• Assuming rest machining drills holes

2. Which of the following is the correct way to specify a block range for rest machining in a CNC program?

easy

A. G71 P100 Q200 U-0.5 W-0.3

B. G71 P100 Q200 U0.5 W0.3

C. G71 U0.5 W0.3 P100 Q200

D. G71 P200 Q100 U0.5 W0.3

Solution

1. Step 1: Identify correct block range order

   In G71, P is the start block number, Q is the end block number; P must be less than Q.

2. Step 2: Check allowance values

   U and W specify allowances and must be positive for rest machining.

3. Final Answer:

   G71 P100 Q200 U0.5 W0.3 -> Option B

4. Quick Check:

   Start block < end block and positive allowances [OK]

Hint: Start block P < end block Q; allowances positive [OK]

Common Mistakes:

• Swapping P and Q values
• Using negative allowance values
• Placing parameters in wrong order

3. Given the following CNC code snippet for rest machining:

G71 P150 Q180 U0.2 W0.1
N150 G01 X50 Z-20
N160 G01 X55 Z-25
N170 G01 X60 Z-30
N180 G01 X65 Z-35

Which blocks will be used for rest machining?

medium

A. Blocks N150 to N180

B. Blocks N100 to N150

C. Blocks N160 to N170

D. Blocks N180 to N200

Solution

1. Step 1: Identify block range from G71 command

   G71 specifies P150 and Q180, meaning blocks from N150 to N180 are selected.

2. Step 2: Confirm blocks exist in code

   Blocks N150, N160, N170, and N180 are present and will be used.

3. Final Answer:

   Blocks N150 to N180 -> Option A

4. Quick Check:

   Block range P150-Q180 matches blocks used [OK]

Hint: Use blocks between P and Q numbers inclusive [OK]

Common Mistakes:

• Choosing blocks outside P-Q range
• Selecting only middle blocks
• Ignoring block numbers in code

4. Identify the error in this rest machining code snippet:

G71 P200 Q180 U0.3 W0.2
N180 G01 X40 Z-15
N190 G01 X45 Z-20
N200 G01 X50 Z-25

medium

A. G71 command is missing

B. Allowance values U and W are negative

C. Block numbers are missing

D. Start block P is greater than end block Q

Solution

1. Step 1: Check block range order in G71

   P=200 and Q=180 means start block is after end block, which is invalid.

2. Step 2: Verify allowance values and blocks

   U and W are positive; blocks N180, N190, N200 exist, so no error there.

3. Final Answer:

   Start block P is greater than end block Q -> Option D

4. Quick Check:

   Start block must be less than end block [OK]

Hint: Ensure P < Q in block range for rest machining [OK]

Common Mistakes:

• Reversing P and Q values
• Assuming negative allowances are allowed
• Ignoring block numbering order

5. You have a rough machining program that leaves a small amount of material on the surface. To optimize the finishing process using rest machining, which approach is best?

hard

A. Skip rest machining and do a full finish pass over the whole part

B. Apply rest machining over the entire rough machining block range with large allowances

C. Use rest machining with block range covering only leftover areas and small allowances

D. Use rest machining without specifying block ranges or allowances

Solution

1. Step 1: Understand rest machining goal

   Rest machining targets only leftover material to save time and improve finish.

2. Step 2: Choose block range and allowances carefully

   Select block range that covers leftover areas only and use small allowances to avoid overcutting.

3. Final Answer:

   Use rest machining with block range covering only leftover areas and small allowances -> Option C

4. Quick Check:

   Target leftover with precise range and allowances [OK]

Hint: Focus rest machining on leftover areas with tight allowances [OK]

Common Mistakes:

• Using large allowances causing excess cutting
• Applying rest machining to entire rough range wasting time
• Not specifying block ranges causing full part machining