What follows is a list of recommended design practices for milled parts. The list is not exhaustive, but is what our staff has found to be most useful.
- Design milled areas so that the end mill required is limited to 3:1 in length to diameter ratio. As shown in the figure below, longer end mills are prone to chatter.
If long end mills cannot be avoided, the following clearances can be
implemented:
- When designing a three-edge inside corner, one of the inside edges must have the radius of the end mill. This is illustrated below. Also shown below is how a separate hole can serve to allow relief for a male ninety-degree corner to fit. The hole must be drilled first since drills cannot withstand significant side loading.
- As with all machining operations, standard tool bit sizes should be used wherever possible.
- Where possible, allow inside radii to be determined by the fabrication personnel. This allows for flexibility to use tools that are easily obtained and maintained.
- For machined surfaces with a high degree of flatness, bosses should be used. This clearly defines what areas need to be flatness controlled, and simplifies painting and other finishing operations.
- For outside corners, chamfers are preferable over radii, as shown below. An outside radius requires a form-relieved cutter and a precise setup, both of which are expensive.
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