CNC Machining - A Complete Guide

Maqsood Mohammed

Maqsood Mohammed

17th May 2021 · 7 min read

A Complete Guide to CNC Machining, different types of CNC machining, how to select the material, tolerance and surface finishing.

CNC Machining - A Complete Guide

CNC Machining - A Complete Guide

CNC machining is one of the popular terms in the manufacturing industry. In the era of technical innovations, CNC machining has bought a wave of revolution in the entire industrial manufacturing industry. It is nothing but computerised control of manufacturing machining tools such as lathes, boring tools, drills, etc. In CNC machining, operation of machining tools are automated and controlled by software. It makes industrial production more precise, cost-effective and helps in bulk production of identical products or parts. If you have made your mind to get your product engineered with CNC machining, here are a few things you must know about CNC machining and CNC machine components.

Material Selection

The most essential and crucial step is selecting the appropriate material as per the product requirement. With the use of CNC machining, you can produce products/parts with a variety of materials ranging from Plastic, Stainless steel and several other raw materials. While selecting material, you need to analyse the properties required in your product based on the use. E.g. if your product is for outdoors, the material should be rust-free. If you are producing parts for the healthcare industry, the material should be as per the regulatory standards. Material selection involves three basic steps:

Define your material requirement:

As per your product requirement and design, access the material quality based on various parameters such as temperature, weight, strength, environmental conditions, etc. List down the properties and parameters.

1. Make a list of qualified material:

List down the names of materials which fulfil all the prerequisites and possess every essential property.

Once you have listed all the competitive materials with nearly all the essential properties you need, analyse the costings. Choose the material which is most suitable and cost-effective.

Some of the common materials used in CNC machining productions are as follows:

Aluminium (Aluminium 6061- T6, Aluminium 7075-T6, Aluminium 6082, Aluminium 5083, Aluminium 2024)

Stainless steel (Stainless steel 304L, Stainless steel 303, Stainless steel 316L)

Alloy steel (Alloy steel 4140, Alloy steel 4340)

Mild steel (Mild steel 1018, Mild steel 1045)

Tool steel (Tool steel D2, Tool steel A2)

Brass ( Brass C360)

Plastics(ABS, Polycarbonate, Nylon6, Delrin and PEEK etc.)

Type of CNC machine used:

Depending on the design of part/product, various types of CNC machines are used to cut the material. Most commonly used CNC machinings are as follows:

3-Axis CNC milling machine

3-Axis CNC milling machines are the most widely used machines. These are popular for producing standard geometric designs. The machine works on three axes X, Y and Z. It is comparatively easier to operate and program. It is cost-effective when the product doesn’t need more rotation. Due to having three workable access, it’s functioning, and product designing has structural restrictions. It is most commonly used to produce mechanical parts, milling slots and drilling holes etc.

CNC turning machine

CNC turning machines are generally preferred over CNC milling machines because of being highly efficient and cost-friendly for bulk production. Along with some benefits, CNC lathes also have their own limitations when it comes to product/part designing. CNC lathes can only manufacture products with cylindrical profiles such as washers, think screws, etc. In cases where products designing require more features, additional CNC milling machines are used in a separate step.

5- Axis CNC machine:

In 5-Axis CNC machine, cutting tools can cut the piece in 5 directions, i.e. it can move around all the three axes, X, Y and Z. The tool can also rotate along two additional axes, i.e. A and B. 5-Axis CNC machine has high precision and efficiency in designing as they possess a higher degree of freedom when compared to 3-Axis CNC machine components or CNC turning machines.

Determining the tolerance requirement

Once you have selected material and kind of CNC machine you want to use for production, another most important criteria is to determine the tolerance requirement of the part/ product you wish to manufacture. It might not sound crucial to you, but it can affect the production cost drastically. You should know that how much tolerance your product requires considering all the use cases and conditions. Tolerance is generally determined by the designer based on the dimensions, function and other details of the part/product.

Determining tolerance is a crucial step because tighter tolerance requires special measurement tools, increased scrap, additional fixturing, etc. Additional requirements enhance budget. Based on the additional requirements and geometry, the costing can increase significantly. Thus, keeping a budget and specification in mind, one should only opt for tighter tolerance when it is an essential requirement to meet design criteria.

Here are the key points you should know about the tolerance of CNC machined components:

  • Tighter tolerances require additional set-up, higher processing time and consume more cycle times. It enhances costing significantly.
  • Always opt for standardized tolerances, until your design requires additional tolerance, as tighter tolerances decrease the ease of production.
  • Some features are complex to design and measure. To measure such features, you may require a specialised instrument that will add additional cost to the budget.
  • The ease of manufacturing a part/product with predetermined tolerance is entirely dependent on the material used in the production. The more soft material, the more it is challenging to give specified tolerance value. Materials like nylon, plastics, PEEK and HDPE, etc. can not hold as tight tolerances as steel or aluminium can.

Surface Finishing

Surface finishing is applied once the product machining is done. Surface finishing is important for CNC machined products because it can bring significant changes in the appearance and surface properties of the product. Here are the most common surface finishing processes

Standard As Machined

Machined products have rough surfaces due to the marks of cutting tools. The quality of the product’s surface is measured in terms of average surface roughness (Ra). Ra is a measurement unit to assess the deviation from the ideal surface. Generally standard as machined products have an average surface roughness of 3.2μm that could be reduced up to 0.4μm by using finishing cutting pass. The reduction in roughness will require additional cost.

Bead Blast Finish

Bead blast finishing makes the rough surface smoother and adds matte or satin textures. As the name suggests, it uses glass beads to correct the cutting tool marks of the product surface. The glass beads are bombarded on the surface with a high-pressure air gun. Some material might be removed to give a smooth texture to the surface. Bead blastic is a manual procedure of smoothening. It is mainly utilised for visual purposes, and the result entirely depends on the skills of the operator


Anodizing is a surface finishing method that adds a thin ceramic layer on the metal surface. It protects the metal surface from corrosion, as the anodic coating is electrically non-conductive. The coating can be dyed with various colours. Anodizing surface finishing method is only compatible with titanium and aluminium.

Powder coating

In the powder coating process, the surface gets coated with a protective layer of polymer. The protective layer provides protection against all kinds of wear and tear. The powder coating technique is compatible with all types of material. It can also be combined with bead blasting technique to create a uniform and smooth surface.

With the help of these four steps, you can plan to manufacture your product. If you are planning to get your CNC machined products and seeking further assistance, upload your 3D files at Custiv and let us have your back in the rest of the process. We will ensure to get your part/product manufactured in the pre-vetted global manufacturing plants.

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