We all know that CNC cutting is a relatively important machining process in CNC lathe processing. Many workpieces will be processed by CNC cutting lathes. The CNC cutting process requires us to master a lot of operating skills. The mastery of these skills will help us to be more perfect. Below we summarize the common problems and improvement methods of CNC machining process, and how to choose the three important factors of speed, feed and depth of cut in different application areas.

1. Reasons for overcutting of CNC cutting workpieces:

1. Flick knife, the tool strength is not too long or too small, causing the tool to flick.

2. Improper operation by the operator.

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

4. The cutting parameters are improper. (Such as: the tolerance is too large, the SF setting is too fast, etc.)


1. The principle of using a knife: can be big or small, can be short but not long.

2. Add the corner cleaning program, and keep the margin as evenly as possible. (Leave the same margin on the side and bottom)

3. Reasonably adjust cutting parameters, and round corners with large margins.

4. Using the SF function of the machine tool, the operator fine-tunes the speed so that the machine tool can achieve the best cutting effect.


Second, the problem of CNC cutting

1. Inaccurate during manual operation by the operator.

2. There are burrs around the mold.

3. The middle rod has magnetism.

4. The four sides of the mold are not vertical.


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

2. Deburr the periphery of the mold with oilstone or a file, wipe it clean with a rag, and finally confirm it by hand.

3. Demagnetize the centering rod before centering the mold. (Ceramic centring rod or others can be used)

4. Calibrate to check whether the four sides of the mold are vertical. (Large verticality error needs to review the plan with the fitter)


Three, CNC cutting tool setting problem

1. Inaccurate during manual operation by the operator.

2. The tool clamping is wrong.

3. The blade on the flying knife is wrong. (The flying knife itself has a certain error)

4. There is an error between the R knife and the flat-bottom knife and the flying knife.


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

2. When the tool is clamped, blow it with an air gun or wipe it with a rag.

3. One blade can be used when the upper blade of the flying knife needs to measure the blade and the light bottom surface.

4. A separate tool setting program can avoid the error between R knife, flat knife and flying knife.


Fourth, CNC cutting collision machine-the reason for the emergence of programming

1. The safety height is insufficient or not set. (The tool or chuck hits the workpiece when the rapid traverse is G00)

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

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

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

5. The coordinates are set incorrectly during programming.


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

2. The tool on the program sheet must be consistent with the actual program tool. (Try to use automatic program list or use pictures to output program list)

3. Measure the actual processing depth on the workpiece, and write clearly the length of the tool and the blade length on the program sheet. (Generally, the length of the tool holder is 2-3MM higher than the workpiece, and the length of the blade is 0.5-1.0MM)

4. Take the actual number of Z-axis on the workpiece, and write it clearly on the program sheet. (This operation is generally written manually and needs to be checked repeatedly)


Fifth, the collision-the reason for the appearance of the operator

1. Depth Z axis tool setting error·.

2. The number of hits in the score and the number of operations are wrong. (Such as: unilateral fetching without cutting radius, etc.)

3. Use the wrong knife. (For example: D4 knife is processed with D10 knife)

4. The program goes wrong. (Such as: A7.NC has gone to A9.NC)

5. The handwheel is cranked in the wrong direction during manual operation.

6. Press the wrong direction during manual rapid feed. (For example: -X press +X)


1. Be sure to pay attention to the position of the tool in the depth Z-axis tool setting. (Bottom surface, top surface, analysis surface, etc.)

2. Check repeatedly after the count and the operation are completed.

3. When clamping the tool, check it repeatedly with the program sheet and the program before loading it.

4. The program should go one by one in order.

5. When using manual operation, the operator himself should strengthen the operation proficiency of the machine tool.

6. In manual rapid traverse, you can first raise the Z axis to the workpiece and move.


Sixth, CNC cutting surface accuracy problem

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

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

3. The tool clamping is too long, and the blade is too long to avoid the air.

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

5. Programming the tool movement mode. (Climb milling can be considered as far as possible)

6. The workpiece has burrs.



1. The cutting parameters, tolerances, margins, 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 as short as possible, and the cutting edge should not be too long.

4. For the down-cutting of flat knife, R knife, and round nose knife, the speed feed setting should be reasonable.

5. The workpiece has burrs: it is directly related to our machine tools, cutting tools, and cutting methods. So we have to understand the performance of the machine tool and make up the edges with burrs.


Seven, the problem of chipping in CNC cutting


1. Feed too fast

2. The feed is too fast at the beginning of cutting

3. Loose clamping (tool)

4. Loose clamping (workpiece)

5. Insufficient rigidity (tool)

6. The cutting edge of the tool is too sharp

7. Insufficient rigidity of machine tool and tool holder


1. Slow down to a suitable feed rate

2. Slow down the feed rate at the beginning of cutting

3. Clamping

4. Use the shortest tool allowed, clamp the shank deeper, and try down milling

5. Change the fragile cutting edge angle, once the edge

6. Use a rigid machine tool and tool holder


8. Causes of CNC wear

1. The machine speed is too fast

2. Hardening material

3. Chip adhesion

4. Improper feed rate (too low)

5. The cutting angle is inappropriate

6. The one-time clearance angle of the tool is too small


1. Slow down and add enough coolant

2. Use advanced knives and tool materials to increase surface treatment methods

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

4. Increase the feed rate and try down milling

5. Change to proper cutting angle

6. Change to a larger rear angle


Nine, the destruction in CNC cutting

1. Feed too fast

2. The cutting amount is too large

3. The blade length and overall length are too large

4. Too much wear


1. Slow down the feed rate

2. Use a smaller cutting amount per edge

3. Clamp the shank deeper, use a short tool, and try down milling

4. Re-grind at the beginning


10. Vibration marks of CNC cutting


1. The feed and cutting speed are too fast

2. Insufficient rigidity (machine tool and tool holder)

3. The back angle is too large

4. Loose clamping


1. Correct the feed and cutting speed

2. Use better machine tools and tool holders or change cutting conditions

3. Change to a smaller relief angle, and process the edge zone (grind the edge with oilstone once

4. Clamp the workpiece