5 Mistakes To Avoid When Designing Machined Parts

Optimize part design to reduce CNC machining time and cost

Designing parts for CNC machining might appear simple, as it involves removing material from a solid block to achieve the desired shape. However, numerous design challenges can occur if manufacturability is not considered.

Our engineering experts have identified several common issues frequently encountered in quote requests. By avoiding these problems, you can enhance your part design, reduce lead times, and potentially save costs.

Avoid the Sharp Internal Corners

Certain features are not feasible with standard CNC machining; a common example is an internal 90° angle. CNC milling tools are cylindrical, resulting in rounded edges rather than sharp, straight angles in the machined cavity. To achieve a precise 90° angle, EDM (electrical discharge machining) is typically used, though it is a more costly process compared to standard CNC machining.

Avoid Designing Thin, Tall Walls

When designing for CNC machining, it is crucial to avoid excessively thin or tall walls. Thin walls might be necessary for specific projects, but studies indicate that wall thickness is directly related to material stiffness, affecting machining accuracy due to vibrations. Typically, the minimum wall thickness is 0.8 mm for metals and 1.5 mm for plastics. Tall walls can lead to problems such as poor surface quality, difficulty in achieving part tolerances, and risks of chipping, bending, or breaking. A recommended guideline for walls is to maintain a width-to-height ratio of 3:1.

Avoid Parts with Unnecessary Tight Tolerances

While CNC machining can achieve very tight tolerances, it’s not always necessary for every part to adhere to the strictest standards. Only applying tight tolerances when essential can significantly cut costs. Higher precision demands more complex manufacturing processes, decreasing production efficiency and increasing expenses. Often, perfect assembly can be accomplished by allowing reasonable gaps, simplifying assembly relationships, and incorporating positioning features. Additionally, maintaining consistent tolerances can reduce machining time.

Avoid the Small and Deep Holes, and the Curved Holes

Avoid designing small, deep holes as they can lead to drill breakage and make chip removal challenging. The hole depth should not exceed three times its diameter. One way to avoid deep holes is by using stepped holes. Blind holes need an additional 25% of their depth for chip storage. Curved holes cannot be machined with CNC methods, but if they are necessary for your design, Electrical Discharge Machining (EDM) can be used, though it will increase production costs.

Avoid the Deep Cavity

CNC cutting tools have a proportional limit for machining depth, achieving optimal performance when the cavity depth is 2-3 times the tool's diameter. Deeper cavities, up to 4 times the tool diameter, are possible but will increase costs, particularly with multi-axis CNC machines. For instance, a milling cutter with a 12mm diameter can effectively machine a cavity up to 25mm deep, with a maximum depth of 48mm.

Summing it Up

No single design tip can solve every practical issue. For further assistance, feel free to CONTACT US for comprehensive and personalized design analysis. To kick off your next design project, simply Upload a 3D CAD model now.