Milling: Design Rules
engineering fundamentals Milling: Design Rules
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Design of Parts for Milling
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.
  1. 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:

     


     
  2. 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.

     


     


     
  3. As with all machining operations, standard tool bit sizes should be used wherever possible.
     
  4. 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.
     
  5. 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.
     

     


     
  6. 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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