Part 2 highlights common practices that focus on manufacturability and cost when designing and creating parts.


A part’s features sometimes make it more difficult to manufacture, or can increase cost and time. Understanding what affects the difficulty, time consumed, and/or cost of a part that needs to be machined is important. The following presents tips on designing parts for manufacturability with vertical milling machines, horizontal milling machines, and lathes. For more information, check out Part 1 of this guide.

Interior Fillets

When using a CNC vertical or horizontal milling machine, all interior vertical walls must have a radius. That’s because a round tool, spinning at high RPMs, is used to remove the material. Designs must take into account areas where radii will occur due to this limitation.

Inside Corner Fillets

For inside corner radii, it may be better to use a non-standard radius. This is because end mills need clearance to turn and continue milling when tracing the internal corner. If a part features a 0.25-in. interior radius, the standard end mill would need to hammer the corner, come to a complete stop, pivot 90 degrees, and then resume cutting. Doing this slows down machining speed, which adds costs and causes vibration. By adding 0.02 in. (0.508 mm) to 0.05 (1.27 mm) in. to internal radii, the cutter will be able to turn slightly without coming to a complete stop. This will not only reduce cost, but also improve CNC parts.

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