Avoid tapping plastic with machine screws where possible

[julianstirling]

We found in OpenFlexure that most of out failures in the field that required re-printing were due to tapping plastic holes with machine screws. The following solutions worked well for us:

• Use Nut traps where possible.
• For small circuits boards like the raspberry Pi, use 2.2mm self tapping screws
• Use triangular holes for tapping into as they are more forgiving if the hole it printed too small.

[hkienle]

Interesting points. Is there a reference for the triangular holes?