Design guide: CNC machining

Design guide: CNC machining

Design guide: CNC machining

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 machined. Some of the considerations for CNC machining:

Design Consideration of design for CNC

Below are the feature list and their respective manufacturing considerations:


The Drawing for these holes should mention the tolerances they have to be in as the mating part could be a press fit or sliding fit or a sliding part.

The Angular Holes are possible for which there should be a butting surface to rest the job at an angle and lock it. The Butting Surface should be Perpendicular to the Hole Axis.

The Wall thickness along beside the hole should be the size of the hole for Steels or Aluminium.

The Holes are machined using a Drill bit or End Mill Tool or a Boring Cutters.

Thread, Tapping & Thread milling

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

Internal threads are made using Tapping Tools Manually after Pre-Drill is made using Milling operation. While External thread is done either using Lathe or CNC Lathe based on the standard or Non standard thread size.

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.


It is best to avoid deep undercuts as this might require special cutting tools to be produced which ultimately increases the Machining cost. Also Undercuts may require multiple setting on the job which increases the time and thereby the cost.

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.

Deep Feature:

While Machining deep features, the cutter may wobble and shank holding length could be very small and therefore may loosen up from the load of chipping the steel. If possible, this can be avoided in design.

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