Analysis of the Causes of CNC Machining Overcutting

Starting from production practice, this article summarizes common problems and improvement methods in CNC machining process, as well as how to choose the three important factors of speed, feed rate, and cutting depth in different application categories for your reference. Article from reference official account: [machining center]

Workpiece over cutting


1. The tool strength is not long or small enough, resulting in the tool bouncing.

2. Improper operator operation.

3. Uneven cutting allowance (such as leaving 0.5 on the side of the curved surface and 0.15 on the bottom).

4. Improper cutting parameters (such as too large tolerance, SF setting too fast, etc.)


5. Principle of using a knife: it can be large but not small, and can be short but not long.

6. Add a corner cleaning program and try to keep the margin as even as possible (with the same margin left on the side and bottom).

7. Reasonably adjust cutting parameters and round off corners with large margin.

8. By utilizing the SF function of the machine tool, the operator can adjust the speed to achieve the best cutting effect.

Middle point problem


1. Manual operation should be carefully checked repeatedly, and the center should be at the same point and height as much as possible.

2. Use an oilstone or file to remove burrs around the mold, wipe it clean with a rag, and finally confirm by hand.

3. Before dividing the mold, demagnetize the dividing rod (using ceramic dividing rods or other materials).

4. Check whether the four sides of the mold are vertical by checking the table (if there is a large verticality error, it is necessary to discuss the plan with the fitter).


5. Inaccurate manual operation by the operator.

6. There are burrs around the mold.

7. The dividing rod has magnetism.

8. The four sides of the mold are not perpendicular. improve:

Crash Machine - Programming


1. The safety height is insufficient or not set (when the tool or chuck collides with the workpiece during rapid feed G00).

2. The tool on the program sheet and the actual program tool are written incorrectly.

3. The tool length (blade length) and actual machining depth on the program sheet are written incorrectly.

4. The depth Z-axis retrieval and actual Z-axis retrieval on the program sheet are written incorrectly.

5. Coordinate setting error during programming.


1. Accurate measurement of the height of the workpiece also ensures that the safe height is above the workpiece.

2. The tools on the program sheet should be consistent with the actual program tools (try to use automatic program sheet or image based program sheet).

3. Measure the actual depth of machining on the workpiece, and write clearly the length and blade length of the tool on the program sheet (generally, the tool clamp length is 2-3mm higher than the workpiece, and the blade length is 0.5-1.0mm away from the blank).

4. Take the actual Z-axis data on the workpiece and write it clearly on the program sheet. (This operation is usually manual and needs to be checked repeatedly.).

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Collision machine - operator


1. Depth Z-axis tool alignment error.

2. Errors in the number of hits and operations during the division (such as unilateral data retrieval without feed radius, etc.).

3. Use the wrong tool (such as using D4 tool to process with D10 tool).

4. The program went wrong (e.g. A7. NC went to A9. NC).

5. During manual operation, the handwheel swings in the wrong direction.

6. When manually rapid feeding, press the wrong direction (such as - X and+X).


1. It is important to pay attention to the position of the depth Z-axis tool alignment. (Bottom, top, analytical surface, etc.).
2. Repeated checks should be carried out after the completion of the middle point collision and operation.
3. When clamping the tool, it is necessary to repeatedly compare and check with the program sheet and program before installing it.
4. The program should be executed in sequence one by one.
5. When using manual operation, the operator should enhance their proficiency in machine tool operation.

When manually moving quickly, the Z-axis can be raised above the workpiece before moving.

Surface accuracy


1. The cutting parameters are unreasonable, and the surface of the workpiece surface is rough.

2. The cutting edge of the tool is not sharp.

3. The tool clamp is too long, and the blade is too long to avoid the gap.

4. Chip removal, blowing, and oil flushing are not good.

5. Programming the tool path method (consider smooth milling as much as possible).

6. The workpiece has burrs.


1. The cutting parameters, tolerances, allowances, and speed feed settings should be reasonable.

2. The tool requires the operator to inspect and replace it irregularly.

3. When clamping the tool, the operator is required to clamp it as short as possible, and the blade should not be too long in the air.

4. For the downward cutting of flat knives, R knives, and round nose knives, the speed feed setting should be reasonable.

5. The workpiece has burrs: it is directly related to our machine tool, cutting tool, and cutting method. So we need to understand the performance of the machine tool and repair the edges with burrs.

Broken blade

Reason and improvement:

1. Feed too fast
--Slow down to the appropriate feed speed
2. Feed too fast at the beginning of cutting
--Slow down the feed speed at the beginning of cutting
3. Loose clamping (tool)
4. Loose clamping (workpiece)


5. Insufficient rigidity (tool)
--Use the shortest allowable knife, clamp the handle a bit deeper, and also try milling clockwise
6. The cutting edge of the tool is too sharp
--Change the fragile cutting edge angle, one blade
7. Insufficient rigidity of machine tool and tool handle
--Use rigid machine tools and tool handles

Wear and tear

Reason and improvement:

1. The machine speed is too fast
--Slow down and add enough coolant.

2. Hardened materials
--Using advanced cutting tools and tool materials to increase surface treatment methods.

3. Chip adhesion
--Change the feed speed, chip size, or use cooling oil or air gun to clean the chips.

4. Improper feed speed (too low)
--Increase the feed speed and try forward milling.

5. Improper cutting angle
--Change to an appropriate cutting angle.

6. The first back angle of the tool is too small
--Change to a larger rear corner.


Reason and improvement:

1. Feed too fast
--Slow down the feed speed.

2. The cutting amount is too large
--Using a smaller amount of cutting per edge.

3. The blade length and overall length are too large
--Clamp the handle a bit deeper and use a short knife to try milling clockwise.

4. Excessive wear and tear
--Grind again in the initial stage.

Vibration pattern

Reason and improvement:

1. The feed and cutting speeds are too fast
--Correction of feed and cutting speed.

2. Insufficient rigidity (machine tool and tool handle)
--Use better machine tools and tool handles or change cutting conditions.

3. The rear corner is too large
--Change to a smaller back angle and machine the cutting edge (grinding the edge once with an oilstone).

4. Loose clamping
--Clamping the workpiece.

Consider speed and feed rate

The interrelationship between the three factors of speed, feed rate, and cutting depth is the most important factor determining the cutting effect. Inappropriate feed rate and speed often lead to reduced production, poor workpiece quality, and significant tool damage.

Use low speed range for:
High hardness materials
Capricious materials
Difficult to cut materials
Heavy cutting
Minimum tool wear
Longest tool life
Use high speed range for
Soft materials
Good surface quality
Smaller tool outer diameter
Light cutting
Workpieces with high brittleness
Manual operation
Maximum processing efficiency
Non-metallic materials

Using high feed rates for
Heavy and rough cutting
Steel structure
Easy to process materials
Rough machining tools
Plane cutting
Low tensile strength materials
Coarse tooth milling cutter
Use low feed rate for
Light machining, precision cutting
Brittle structure
Difficult to process materials
Small cutting tools
Deep groove processing
High tensile strength materials
Precision machining tools

Post time: Apr-13-2023