Why DFM Matters For CNC Machining


CNC machining is a popular rapid prototyping process known for its versatility, repeatability, reliability, and a host of other good attributes. However, these attributes can be improved by having a good design for manufacturing (DfM). 

With a clear focus on DfM, you can enjoy better production efficiency, reduced cost of machined parts, etc., when using CNC machining. Therefore, this blog post will introduce Design for Manufacturing on why it matters in CNC machining and tips that can help you achieve better production efficiency and reduced costs when incorporated in CNC machining. Below are a few things you need to know about DfM in CNC machining.

What is Design for Manufacturing? 

Design for manufacturing (DfM) simply means designing a product in an easy and less costly way. It is widely used in prototype CNC machining, however, it does not only help minimize error in the end. DfM encompasses every part of production that ensures that a product does not have errors and yet is produced at a very low cost. It takes into account five principles; process, design, material environment, and compliance/testing during the designing stage to ensure such results. 

Why Does DfM Matters in CNC Machining?

CNC machining is a process known for its repeatability, reliability, accuracy, precision, etc. However, all these attributes can be improved or, at worst, maintained with DfM. Below are some reasons why DfM matters in CNC machining. 

  • It Makes Sure Your Product Is Manufacturable 

There are scenarios where some products, even with good designs, are not manufacturable. Therefore, many prototype CNC machining companies such as RapidDirect, 3Dhubs, etc., now have DfM in their production plan. 

For some mechanical parts, it can be challenging to achieve a feature necessary for the parts’ functions or performances. Knowing such parts is possible with DfM during the finalization of design drawings and after prototype CNC machining. 

  • Reduce Mistakes Before Production

DFM incorporates all elements of the product’s design, such as mold layouts, heat transfer analysis, tooling design, etc. Consequently, it is easier to notice the errors that could mar product quality after production and avoid it. 

  • It Reduces Lead Time

Without Design for Manufacturing, production will go back and forth in order to judge product quality as there is no means of judging before production. However, with proper verification of the design using DfM, you can eliminate mistakes, save money, and reduce the time it takes to produce and deliver a product to the client. 

Note that while DfM will surely take its own portion of time and effort, it will increase production efficiency overall.

DFM Tips for CNC machining

Below are a few tips to take note of in order to enjoy the benefits of DfM in CNC machining. 

  • Materials

When choosing a material for CNC machining, you must ensure that the material is machinable before selecting it. Therefore, knowing the material properties is a necessary task. For example, copper and aluminum have high machinability, while alloys such as stainless steel and titanium are not easy to machine. 

Checking on the compatibility of the materials with the process will help you reduce production error and increase production efficiency. 

  • Inaccessible Parts Structure

There are some designs that have inaccessible features, such as an inner right angle. This can result in the CNC machine not being able to reach the parts which further leads to production inefficiency and an increase in production cost. Therefore, you should make sure that the CNC machine can access the parts without being blocked. 

  • Sharp Corner

All CNC drills have a circular shape. Consequently, it is difficult to achieve sharp internal corners as the CNC drill will leave a pocket of unmachined space known as the internal corner radius. Some people use other methods such as electrical discharge machining. However, these methods are costly. Therefore, it is better to avoid sharp inside corners whenever possible. 

An ideal rule you could follow is that a corner radius should be slightly larger than the cutter. If it has the same diameter as the cutter, it can lead to premature tool wear. You can also increase the corner radii value by 0.005” (0.127mm). This will give the CNC machine enough movement room.

  • Holes

Holes are machined by a drill bit or an end mill tool. When you have a hole with a non-standard diameter, you should machine it with an end mill tool. For holes deeper than 3mm, use a drill bit. When machining a blind hole, it is better to use a drill bit which will create a cone-shape bottom at 118° or 135°. Also, to avoid error during CNC machining, holes must have a diameter larger than 1mm. 

  • Avoid Thin Walls if Possible

Thin metallic walls in CNC machining will increase chatter and reduce the accuracy of the machining process. For thin plastic walls, it will cause warping or softening. Therefore, it is important to avoid making products with thin walls.

The ideal rule when machining metal is to have a wall thickness of 0.03” (0.762mm). For plastics, you should use 0.06” (1.524mm). While it is possible to machine thin wall sections without much significant risk, it is simply not advisable.

  • Avoid Tight Tolerances If Possible

While you might need a super tight tolerance for some products, it is not proper to always use them. Using a super tight tolerance when not needed will only increase the cost of production. Therefore, it is important that you be reasonable with tolerance.

Most products will do fine under a general tolerance of 0.005.” Increasing this when not needed will only increase the cost of manufacturing your product. Therefore, if not needed, do not ask for it. You can save time, effort, and money by that decision alone while still maintaining quality.

  • Deep Pockets

You should avoid designing parts with deep pockets. When this is an integral part of making a product, the best you could do is to reduce the depth or increase the cross-sectional area of the pocket. 

A rule you could follow is that pocket depth should not be more than thrice the diameter of the smallest tool.


Designing for manufacturing can help improve the manufacturing of products using CNC machining. CNC machining is a process known for its features which include high quality, reliability, and with DfM, you can improve on such attributes. This article introduced CNC machining and DfM, why it matters, and some tips that can help you become more production efficient