Common Problems & Improvement Methods During CNC Machining Process (V1)

Views: 702 Update date: Jun 25,2021

In this article, from the actual production, summarizing the common problems and  methods to improvement, as well as how the three important factors: speed, feed and depth of cutting tool in different applications influence the CNC machining process.

1. Overcut of Workpiece

Ovecut means that the tool cuts the block material which do not need to be cut, causing the workpiece to be damaged. There are many reasons for the over-cutting of workpiece, mainly including low precision of the machine tool, tool collision, spring tool, small tool selected in programming but large tool used in actual processing. In addition, if the operator is not accurate in setting the tool, it may also cause over-cutting.

 cnc machining


Tool Using Principle - Can be Large tool, but not small; can be short tool, but not long.

Add corner cleaning procedures, and leave an even margin as much as possible.

Reasonable adjustment of cutting parameters, leave the margin of large corners rounding.

Use the SF function of the machine, operator can fine-tune the speed so that the machine cutting achieving the best results.

2. Central Division Mistake

Reasons cause in central division of a CNC machine operation:

Operator’s manual operation is not accurate.

Burrs around the mold itself.

The centering bar is magnetic.

The four sides of the mold are not perpendicular.

 cnc machining


Manual operation should be checked repeatedly and the parting should be at the same height at the same point.

Use oil stone or file to remove the burr around the mold, wipe it clean with a rag, and finally confirm by hand.

Demagnetize the centering bar before centering the mold.

Calibration table to check whether the four sides of the mold is vertical. If the perpendicularity error is large, go and review the program with the clampers.

3. Tool Alignment

Problems in tool alignment:

Firstly, the manual operation is mistaken and not accurate.

Secondly, tool clamping error.

Thirdly, flying tool on the blade is wrong, and the tool itself has a certain error.

Fourth, there is an error between R-tool and flat bottom tool and the flying tool.


aluminum cnc


Manual operation should be double checked, and the pair of cutting tool should be at the same point as far as possible.

Tool clamping with air gun below should be cleaned or rag wipe clean.

Flying tool on the blade should measure the tool bar, light bottom surface when a blade is available.

Separate out a pair of tooling program, can avoid the error between the R-tool and flat flying tool.

4. Machine Collision


In the period of CNC programming, machine collision causes by safety height is not enough or not set. Such as the workpiece hit by the tool or collet during fast feed G00. The tool on the program sheet and the actual programmed tool are written wrongly. Besides, wrong number of depth Z-axis on the program list and the actual Z-axis. Also, the incorrect setting of coordinates during programming.



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

The tool on the program sheet and the actual programmed tool should be the same.

Measure the actual depth of machining on the workpiece, and write down the length and edge length of the tool on the program sheet. General tool clamping length is 2-3mm higher than the workpiece, the blade length should avoid empty 0.5-1mm.

Take the actual Z-axis number on the workpiece and write it clearly on the program sheet. This operation is generally a manual operation to write a good to double check.


Common reasons causing the machine collision include,

The depth Z-axis tool alignment error.

Bump number and operator error in the score, for example, single-side taken number without feed radius.

Using the wrong tool, as D4 tool is used to process with D10 tool.

Wrong program, e.g. A7. NC goes the way of A9.NC.

Press the wrong direction during manual rapid feed, such as order -X, but press +X.



Depth Z-axis tool setting must pay attention to what position the tool is on, bottom surface, top surface, analysis surface, etc..

Dividing in the number of touches and manipulation number to be repeatedly checked after completion.

When clamping the tool, should be repeatedly checked against the program list before program loading.

The procedure should be done one by one and in order.

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

When moving manually and quickly, raising the Z-axis to the top of the workpiece before moving.

5. Surface Accuracy

Problems of surface accuracy:

Cutting parameters are unreasonable and the surface of the workpiece is rough.

Tool edge is not sharp enough.

Tool clamping is to long, and the tool edge is to much to avoiding hollow.

Chip evacuation, blowing, and bad oil flushing.

Programming the way of tool processing. (Tip: try to consider taking the smooth milling.)

The workpiece has burrs.

 cnc machining


Cutting parameters, tolerances, allowances, speed feed settings should be reasonable.

The operator is required to check the tool from time to time and replace it from time to time.

The operator is required to clamp the tool as short as possible, and the cutting edge should not be too long to avoid empty.

For undercutting of flat tool, R tool, and round nose tool, the speed feed setting should be reasonable.

The workpiece has burrs: the root of our machine tool, tool, the way to go directly related to the tool. So we have to understand the performance of the machine tool, the burr side to make up the tool.


Above the five common problems and improvement methods about CNC machining processing. As the solution and figure outs are quite essential, there could not be describe all at one article, the next tips will be written in the second version of the same title. Hereby, visit our online site -, or leave us messages at for more information.

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