The development of CNC machining technology offers significant benefits to the manufacturing industry. CNC machines provide engineers and manufacturers with one of the easiest ways to produce metal prototypes or parts. They reduce labors by half and produce precision parts in a much shorter time. When you need to create a kind of airplane wing or a kind of small screw, in quantities from hundreds to millions, CNC online service makes things a lot more efficient and cost-effective. However, creating CAD designs for CNC machining can be very challenging. It requires professionalism, experience, and concentration to prevent any faulty and inaccuracy whilst keeping cost-effectiveness.

In the past few years, we have encountered many problems in doing business with our customers. Some of them came from poor communication and most of the others were caused by the initial design mistakes. We have accumulated lots of experience and summarized some common design mistakes. If you want to make CNC rapid prototype, here are some mistakes to avoid in your design.

Do not design too many thin walls for your CNC rapid prototype

Designers often fail to take into account the possible behaviors of the workpiece during processing. Designing too many thin walls may cause the workpiece to crack, warp, or others.

For example, when machining a CNC rapid prototype from low-stiffness aluminum, the thin walls may snap off or distort in the milling process due to excessive vibration. Reducing the thickness of the wall often result in the decrease of material stiffness, which then leads to increasing the vibration in the machining process and lowering the machining accuracy. One effective way to solve this problem is by keeping a low wall height to length ratio and a low wall height to thickness ratio when you design the thin wall sections of your parts. For reference, an unofficial industry standard of minimum wall thickness is 0.794 mm.

However, for many manufacturing parts, thin walls are crucial. In this case, other manufacturing processes such as sheet metal fabrication can be much more effective as well as economical than CNC online service.

Some features are simply impossible to create using CNC online service

Not all design features can be effectively created using CNC online service. Small features with less than 2mm size are difficult to make by CNC machines because of the limitation of the milling tools. For example, it is hardly possible to create a CNC rapid prototype featuring curved holes. If this feature much be included in your parts, then a method called electric spark machining (EDM) may be a more appropriate solution. EDM is a process that uses electricity to produce desired shapes.

Designing the right tolerance is critical for your CNC rapid prototype

Attainable tolerance varies from CNC machines. Many designers lack general knowledge of the attainable tolerances of difference CNC machines. The inaccurate or excessive tolerance often causes the poorer quality of the machined part. If you use CNC online service to machine your parts, you can consult the service provider to remove unnecessary tolerances from your design, thereby getting higher quality machined results.

In addition, excessive tight tolerance in the design can also be costly to produce and not all parts require demanding tolerances. It is important to consult your CNC machining provider when designing your desired CNC rapid prototype.

Avoiding unnecessary aesthetic features in CNC rapid prototype manufacturing

When considering CNC online service to machine your desired parts, it is necessary to consider the cost of materials and time of processing. Such questions like “this material is used just for aesthetic reason, is it necessary?” and “whether it is completely necessary to have an extra complex feature which requires 5-axis machines to process?” should be taken into serious consideration when designing your CNC rapid prototype.

Unnecessary materials that are used just out of aesthetics reason should be removed as it can be costly and hard to machine, and may cause poor quality of machined parts. Instead of achieving aesthetics directly through CNC online service, some post-machining processes, for example, electro-polishing, can also be used to obtain this purpose. However, not all surface treatment can be applied to each kind of material. For example, painting is not suited to PP material and anodized surface would look good on CNC machined aluminum but not pretty on die-cast aluminum.

Do not design too deep cavities for your CNC rapid prototype

The cutting length of CNC tools is limited. Milling tools are commonly the most efficient tools in machining CNC rapid prototype. They can mill cavities twice or three times deeper than their diameter. For example, a milling tool of 15mm in depth can cut cavities up to 35mm deep. However, the deep cavity milling might cause the cutting tool to be unable to reach the milled surface, cause tool deflection due to the excessive extension of the tool from its clamp, and could result in troubles of evacuating chip. Here are some possible solutions to this problem:

1. Gradually lower the end mill in smaller and smaller increments;

2. Use a cutting tool of sufficient size or an extended tool holder;

3. Use other machining methods such as EDM;

Whether you are a total newbie looking for CNC online service to get your first CNC machining project started or a professional seeking for a bit guidance, the design of CNC rapid prototype is an ongoing learning process for both beginners and experts. This article will help you avoid many design mistakes, create the right design efficiently thereby getting high-quality CNC machined results.