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Radmot Aug 9, 2023 12:47:29 PM

CNC grinding - smoothing tool marks on machined parts

CNC grinding (sometimes called CNC sanding) of the surface of machined parts is usually one of the final processes in manufacturing. That form of machining focuses on smoothing surface and removal of tool marks (eg. cutters, bits).

Just like other forms of machining, grinding can be executed manually, with power tools (hand-hed or stationary) and numerically controlled devices. CNC grinding allows the final machining process to be much more efficient and deliver a high quality surface.

CNC grinding: what is that process and how differs from traditional?

Samo szlifowanie CNC dzieli się ze względu na sposób pracy głowicy wygładzającej na: 

Grinding itself is a type of machining – focused on removing small surface irregularities. That process is called an abrasive treatment and relies on removing material with grains or blades of undefined geometry and number.

Grinding is characterized with low depth of machining – that is why that type of processing is used often in the finishing steps to make a smooth surface of a part.

Traditional grinding (often called "sanding") is executed with a vast variety of abrasive and machine tools – files, sanding discs and polishing pastes. Numerically controlled grinding operation is much more complicated yet allows to speed up the whole process.

The reason is simple: CNC grinders are controlled by a computer and should be
programmed accordingly. That is why such devices can provide high precision of removing material and deliver almost spotless surface quality even on larger surfaces made of a vast variety of materials.

CNC systems also provide better repeatability of the whole process, especially in comparison to automatic (with usage of power tools) and manual sanding. Such a feature is crucial in manufacturing big batches of parts that should be manufactured within tightest tolerances (below 0.02 mm). CNC grinding machines type of work can be divided on:

  • CNC profile grinding – that provides high precision and smoothness of the surface. That processing is used to finish flat surfaces and the sanding head is positioned stationary in relation to grinded element,
  • CNC round grinding – used to polish holes or other cylindrical spaces (internal and external) used during machining. Allow to achieve smooth finish in area (eg. cylinder holes in the engine block),
  • CNC flat grinding – similar to profile grinding, but machined object is stationary in relation to the moving grinding/sanding tool.

Each of the mentioned methods allow precise grinding and good quality of the achieved finish.

Practically every material can be grinded – stainless steel, aluminum alloys, titanium, wood, etc. Of course – grinding tools will differ between the applications, eg. metal alloys should be harder and more wear resistant to provide efficient surface grinding.

It is worth mentioning the grinding is usually one of the last steps of machining parts but should not be performed after processes that better the surface. Thermo-chemical betterin of the surface – like anodization – creates a tin coat on the surface that would be damaged by abrasive tools. Better choice to improve smoothness of the surface is polishing.

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Tools used for grinding: files, sanding paper and CNC grinders

Tools used for finishing surfaces can be categorized as:

  • handheld tools – files, sanding paper, etc.,
  • handheld power tools – like disk sander, angle grinder, etc.,
  • stationary power tools – desk/automatic grinder with multiple grinding applications,
  • finally - CNC grinders. 

On top of differences in the operation (handheld tools require more labor to achieve results; CNC grinding machines can work more efficiently but require longer preparations), important are the parameters of the grinding surface.

One of the most important of these is a grammage – the size of grains that remove the excess of material from the surface and make it smooth. The most common categorisation remain attaching that parameter to the step of machining: 

  • to initial grinding, that require removing visible machine marks, is often used very raw, up to P50;
  • to more precise grinding, that require good/smooth surface, are used grinding surfaces of grammature from P60 fo P240,
  • to achieve a very smooth surface often are used very fine sanding tools (grammage from P240 to P2500). It is worth mentioning that working with higher grammage it is advisable to moist the polishing surface (eg. kerosine or water; that process is called we grinding).


CNC grinding - contact us

In RADMOT we offer professional CNC milling, CNC turning, and many additional services like aluminum anodization, laser marking, and assembly. 

Send us a quote and tell us what type of CNC machined parts you need. We have offered professional CNC services for over 40 years and our quotation is completely free

If you have any questions regarding CNC manufacturing processes – send us a question: and we will help you to understand it better. Our knowledge is at your service.

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