Manufacturing prototypes and production parts fast and cost-efficiently is often a balancing act of quick-turn CNC machining capabilities and an optimized part designed for those capabilities. As such, there are a handful of important considerations when designing parts for Protolabs’ milling and turning processes that can accelerate production time while reducing costs.
Tip 1: Avoid thin, vertical walls
In general, thin walls are tough to handle. However, they become more of a burden when they are oriented vertically (or perpendicular to the machine’s work table). Walls that are less than 0.0625-inch thick are likely to deflect during machining and result in tool chatter that can leave behind unappealing scars and surface blemishes. For high-quality surface finishes, wall thicknesses should be 0.0625-inch thick or greater
Tip 2: Avoid small/tightly packed features at deep depths.
The deeper the pocket, the longer the run time. Maximum tool length-to-diameter ratios should not exceed 6:1 (for example, a 0.5-inch end mill cutting 3 inches deep). Tight corners or small features at the bottom of the cavity are very tough to mill. Tools can often be custom ordered or ground back to achieve longer depths but that significantly increases machine time and part cost.
Tip 3: Design around sharp internal corners
In some cases, an assembly might require sharp internal corners. This can be accommodated without resorting to costly EDM operations. One method is to “mouse-ear” or “dog-bone” the corners as shown in the image above. This will result in a small bubble of removed material where the corner used to be that, if acceptable, will enable the mating components to fit.
Tip 4: Mind tapping depths.
Tapping depths follow even stricter guidelines than traditional drilling or milling. Taps are very hard to thread consistently at aspect ratios greater than 2.5:1. If a 1/4-20 UNC thread must extend through the depth of a 1-inch plate, consider including some clearance to minimize thread engagement.
Tip 5: Consider using stand-offs or mating parts
Although it’s appealing to create a part from one piece of material, production might be more cost-effective to design it in multiple pieces. For a plate that is 0.0625-inch thick, but requires clearance for positioning additional assembly components, consider using stand-offs in lieu of machining the posts from a much larger stock size. This can save material and machining time.