5 mistakes to avoid when designing machined parts

Upload the CAD model to our automatic quotation and design analysis engine, and our CNC machine will mill or process your parts in one day. However, for all the technologies that make it possible, the human factor is still crucial and is often the culprit for the recurring problems we see in cold forged parts. Avoiding these 5 common mistakes can help improve design, shorten run time, and possibly reduce final manufacturing costs.


1. Avoid functions that require unnecessary processing

A common mistake is to design a part that does not require machine cutting. This unnecessary processing will increase the running time of the part, which is a key driver of the final production cost. Consider this example, where the design specifies the key circular geometry required for the part application (see image below). It requires machining a square hole/feature in the middle and then cutting off the surrounding material to expose the finished product. However, this method adds a lot of running time to process the remaining material. In a simpler design (see picture below), the machine only needs to cut parts from the block, without the need for additional, wasteful processing of excess material. The design change in this example cut the machine time by nearly half. Keep the design simple to avoid extra running time, meaningless processing and increased costs.

2. Avoid small or raised text

Your part may require a processed part number, description, or company logo. Or you might think that some text looks cool in a certain part. However, adding text will also increase costs. The smaller the text, the higher the cost. This is because the very small end mills required to cut the text run at a relatively slow speed, increasing the running time and thus increasing the final cost. However, if your part can accommodate larger text, the speed of cutting larger text will be significantly faster, thereby reducing costs. When possible, choose concave rather than convex text, which requires grinding away the material to create letters or numbers on the part.

3. Avoid tall and thin walls

Wall features in part design are usually tricky. The cutting tools used in CNC machine tools are made of hard and rigid materials, such as tungsten carbide and high-speed steel. Nevertheless, the tool will slightly deflect or bend under the action of the machining force, as does the cutting material. This can cause problems such as unwanted corrugated surfaces and difficulty meeting part tolerances. The walls may also chip, bend, or break.

The higher the wall, the greater the thickness required to increase the stiffness of the material. Walls of 0.508 mm or smaller are easily broken during processing, and may subsequently bend or warp. Try not to design walls that are too thick, because the cutters usually rotate at 10,000 to 15,000 rpm. The rule of thumb for walls is a 3:1 aspect ratio. Add a 1°, 2°, or 3° draft angle to the wall to make it tapered instead of being placed vertically, so that it can be processed more easily and leaves less residual material

4. Avoid using small features that you may not need

Some parts contain square corners or small internal corner grooves to reduce overall weight or accommodate other components. However, the internal 90° angle and small grooves are too small for our large tools. Creating these means using smaller and smaller tools to pick up corner materials. This may result in the use of six to eight different knives. All these tool changes will increase runtime. To avoid this, first determine the importance of the groove. If they are just to reduce weight, please re-examine your design and avoid paying for machine materials that do not need to be cut.



5. Reconsider the final molded part

Before purchasing a mold, we often see the design of injection molded parts uploaded to our processing services for prototyping. But each process has different design requirements, and the results may also be different. When forming, thick machined features may show depressions, warpages, pores, or other problems. A well-designed molded plastic part with ribs, grooves, and other features requires a long running time to process.

The point here is that part design is usually optimized for its manufacturing process. You can consult our team first to learn how to modify the design of mold parts for mechanical processing, or only prototype injection molding parts in the final production process.