How to create perfect products through CNC machining and the tips for inspection that you have to know!

How to create perfect products through CNC machining and the tips for inspection that you have to know!

No matter what specific kind of matter it is, whether it is metal or plastic, CNC machining has the remarkable ability to fabricate it precisely for you.


However, how exactly do we go about evaluating whether the requirements of the CNC machined products have been successfully met? This article will comprehensively present HTM’s meticulous inspection specifications for CNC machined parts.


In order to achieve a full 100% of qualified products through the intricate process of CNC machining, HTM painstakingly formulates the inspection specifications for CNC machined parts by drawing upon ISO9001;2015 and our wealth of accumulated years of invaluable experience. It serves as the definitive machining standard and inspection standard for CNC machined products, offering reliable benchmarks for dimension verification and appearance inspection for QC engineers. Each and every quality inspector of HTM undergoes rigorous professional training prior to commencing their work duties, and this is precisely the reason why our products have managed to earn the unwavering trust of countless thousands of customers spanning the globe.


Inspection items and the detailed definition of common defects in CNC machining


Cutting marks: These are distinct marks that are typically caused by cutter abrasion or erratic swing. They are often palpable, presenting themselves in a wavy pattern that is easily discernible.


Crash: These are the telltale subsidence areas that emerge when there is improper handling with incidents such as crashing or dropping during the machining process.


Air hole, sand hole: These are irregular pore-shaped flaws or cellular black-spots that occur due to an insufficiency in the casting density.


Scratch: These are the strip-like defects that are brought about by the friction of the product during improper operation. It could also be caused by the residual cutting waste around the cutter that results in spiral linear defects.


Mismatch (step): This refers to the “step” defects that are caused when the joining of the cutting paths is not smooth and seamless.


Burr/flash: These are serrated or strip-like defects that are generated when a portion of the cutting waste fails to detach from the part under the radial force exerted by the cutter.


Short shot: This occurs when there is excessive cutting stress after the cutter has been worn, leading to a collapse or a lack of material around the worn areas of the part.


Thread damage: This can include a rather small or large bottom hole of the tapping, a skewed bottom hole, or wear on the tap that causes partial thread disorders, missing threads, or thread mismatches and so on.


Crush: This is when cutting residues are left on the machining jigs or an external force causes impurities to be pressed into the product, forming sunken defects that are clearly visible.


Crack: This can be caused by insufficient casting density or cutter abrasion that leads to overly large cutting stress and subsequently results in tearing defects that are both obvious and detrimental.


Defective cutting: This can occur when the position of the part that is fixed is skewed or when there is a change in the relative coordinates of the cutter, which then leads to either excessive cutting or insufficient cutting (also known as excessive material).


Hole deviation: This can happen when there is improper positioning or a slanted reinforcing column, or even when there is uneven shrinkage in die-cast parts that causes the hole position to deviate from the center of the strengthening column where the hole is located.


Defective chamfer: For the purposes of assembly or safety, the sharp edges of the part are chamfered. If there are no specific requirements on the drawing, the thread chamfering should be controlled according to C0.2±0.1, and the tapping flash should not be higher than the top surface of the screw column (that is to say, the height of the flash should be lower than that of the chamfering).


Threaded flat (shallow threaded): This is when there is a large screw bottom hole that causes thread slippage or insufficient thread torque, and when visually inspected, the thread appears as a cone platform.


Structure mismatch: This is when the product does not conform to the 3D drawing. Common mismatches include excessive material, missing material, and issues with the roundness of holes (such as rollers or pillars).


Distortion: After machining, due to the influence of the part material, the thickness and toughness of the part change, which leads to a deviation from the initial shape of the part and ultimately causes an uneven or distorted product shape.


Classification of part surface:


A surface: This is the surface part that is directly exposed to the outside after assembly, and is generally referred to as the appearance.


B surface: This is the surface part that is not directly exposed to the outside after assembly, but can be directly seen when rotated at a certain angle.


C surface: This is the part surface that is not directly exposed to the outside after assembly, and can only be seen after disassembling some parts.


Acceptance standards and defect grades of CNC machined parts

CNC machining defect grades


Standards for CNC machining process

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Appearance inspection standards for CNC machining

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Lily Zhao

Lily Zhao

Hello everyone, I'm Zhao Lili, the webmaster of You can call me Lili. I have more than 15 years of rich experience in the field of CNC machining. Our company is a professional company that focuses on precision CNC machining, the design and manufacture of peripheral equipment of CNC machine tools, the system integration and automation of equipment, and the precision machining of mechanical parts.

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