6 Mistakes to Avoid When Designing Machined Parts
Upload a CAD model to our inbox and our CNC machines will mill or turn your part as fast as possible. However, with all the technology that makes it possible, the human element is still critical – and is often the culprit behind the recurring problems we see in parts designed for CNC machining. Avoiding these six common mistakes can help improve designs, reduce run times and potentially reduce final manufacturing costs.
1. Avoid Features that Require Unnecessary Machining
One frequent mistake is designing a part with areas that don’t need machine cutting. Such unnecessary machining adds to your part’s run time—run time that’s a key driver of your final production cost. Consider this example, where the design specifies a critical circular geometry needed for the part’s application (see left-side illustration in image at right). It calls for machining the square holes/features in the middle and then cutting away the surrounding material to reveal the finished part. That approach, however, adds significant run time to machine away the remaining material. In a simpler design (see right-side illustration at right), the machine simply cuts the part from the block, eliminating the need for additional, wasteful machining of excess material altogether. The design change in this example cuts machine time nearly in half. Keep your design simple to avoid extra run time, pointless machining—and added cost.
3. Avoid Tall, Thin Walls
Wall features on part designs are generally tricky. Cutting tools used in the CNC machines are made of hard, rigid materials such as tungsten carbide and high-speed steel. Nonetheless the tools deflect or bend slightly at machining forces, as does the material they’re cutting. This can result in issues such as an undesirable rippled surface and difficulty meeting part tolerances. The wall also could chip, bend, or break. The taller your wall—our maximum is 2 in. (51mm)—the thicker it may need to be to increase the rigidity of the material. Thin walls of 0.020 in. (0.508mm) or less are subject to breaking during machining and may flex or warp afterwards. Try not to design walls too thick as the cutting tool usually is spinning at 10,000 to 15,000 rpm. A good rule of thumb for walls is a width-to-height ratio of 3:1. Adding some draft to a wall—an angle of 1, 2, or 3 degrees so that it tapers rather than standing vertical—could make machining it easier and leave less leftover material.
4. Avoid Small Pocket Features You May Not Need
Some parts incorporate square corners or small internal corner pockets to reduce overall weight or to accept other pieces of an assembly. Internal, 90-degree corners and small pockets, however, are too small for our larger cutting tools. Creating those means picking away at the corner material with smaller and smaller tools. That could result in using six to eight different cutting tools. All of those tool changes drive up run time— and you guessed it—your project’s cost. To avoid this, first determine how critical the pockets really are. If they are there only to reduce weight, revisit your design to avoid paying to machine material that doesn’t need to be cut. The larger the corner radius you design, the bigger the cutting tool we can use, and the less run time it will take.
5. Avoid creating holes that cannot be threaded
We can easily add threaded holes to your machined parts. However, designing threads so that we can see them and make them available to be machined into your part can be a challenge. Our quick turn process has a static set of threads available. When our software analyses your part, it looks for a hole diameter that corresponds to one of these threads.
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