Rob Kempinski writes ...
>> The cutting angle of a drill for plastic should be
>>>vertical such that it actually scapes the plastic away. They sell em, or
>>>you can modifiy an old drill bit.
But...
The included angle of a standard drill bit is 118 deg. For harder steel we
use 135 deg. For plastic we regrind drills to something closer to 90 deg.
The less the included angle, the more it wants to follow the spiral of the
drill !!
Where it's going to break the lens is when you break through the other side.
Machinery Handbook might have some discourse on the subject.
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