Design guide: CNC machining

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CNC Machining

CNC machining is the manufacturing technology of subtractive method, it removes the material to produce the part as in the cad model. It is a method to obtain high complex products in high quality in a short period of time. Both metal and plastic material can be machine. Some of the considerations for cnc machining:

Design Consideration of design for CNC

Mainly designing the product for cnc machining, the Geometric tolerance should be considered.


This is one of the important points to take while designing the product. The hole should be designed on the basic consideration of direction, angle, depth & also the standard pitch. Holes are machined using a drill pit or end mill tool. As a designer you should be have the knowledge of standard hole sizes

Thread, Tapping & Thread milling

There are two basic types of machined threads: internal threads and external thread

Thread length is necessary when designing the part Deep threaded holes can increase part cost as specialized tooling may be needed to meet the depth requirements. Try to use off-the-shelf thread sizes wherever possible to keep costs down.


Try to avoid deep undercuts as this might require special cutting tools to be produced which ultimately increases the Machining cost. Also Try to give minimal draft angle for undercuts since this may also require a special tool to be built or it may also increase the CNC running cost.
Some features cannot be reached by a standard

Chamfer and Fillet


Maintain Minimum Chamfer of 1X45° on all sharp corners so the operator doesn’t get injured while handling the part. Also, it may avoid breakage of parts while doing deburring.


Try to avoid external radius as the CNC running hours may increase. For internal radius maintain a minimum radius of R2 since these tools are generally available ones. In general, the radius of the internal fillet should be greater than 1/3 of the depth of the cavity to avoid tool-breakage.

The chamfer is given for avoiding the sharp corners and also to reduce the risk of Injury who is handling the part. While the deburring process there is a breakage on edges of the parts. The fillet is a round shape edge, in general the radius of the internal fillet should be greater than 1/3 of the depth of the cavity to avoid tool-breakage.

Avoid thin walls

When machining the thin wall will be the major issue and thus it should be avoided as much as possible while designing. For cnc machining the minimum wall thickness for metal is 0.8mm and for plastic is 1.5mm. Higher Wall thickness will avoid breakage of parts from the high vibration.

Detail design

During the design process, utmost care and accuracy must be maintained at all times which determines the quality and required output. CNC machining requires. Direction, angle, inner dimension (depth), standard hole size, undercut detail dimensions in the 2D Drawings apart from STP File.