The automation machinery designers will design assembly datum features into parts where accuracies are needed for assembly. For this, abilities to design the assembly datum features that are: (1) easy to machine, (2) easy to assemble, (3) low in manufacturing costs will be needed.

Explanations on assembly datum features that are easy to machine

a) Obtaining datum accuracies

• Choose accurate machine tools in order to accurately machine the parts with assembly datum features.

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Utilize the inherent positioning accuracy characteristics of accurate machine tools to obtain high accuracies of the parts with assembly datum features.

-Explanation
Machine tools use precision guides for accurate motion and precision measurement instruments for accurate positional detection to move the cutting tools in desired manner to obtain the targeted shapes accurately. For this reason, the machines that produce highly precise parts are called "Mother machines"

-Examples
Hole position accuracy: ±0.5mm > Drill press
Hole position accuracy: ±0.01mm > CNC Milling machine
Hole position accuracy: ±0.005mm > Jig boring machine
Datum plane accuracy: ±0.01mm > CNC Milling machine
Datum plane accuracy: ±0.005mm > Precision flat grinder

b) Easy machine assembly datum designs

• Utilize the inherent accuracy of the machine tools for parts accuracy.
• Use the external profile (or datum reference holes) features as the datum surfaces, and measure from these surfaces to machine the assembly datum features. (2 red lines show in Fig. are the datum lines)
• Therefore, an easy to machine design is where all the datum locations can be machined at once while the part is mounted on a machining fixture.
• If a fixtured part must be unfixtured and reset (ex. reversing), resetting error will result.

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Highly accurate and cost effective part designs are where the parts' all datum features can be machined at once with one time fixturing.