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MICROmachining
By Patrick Lemos,
Prime Axis Manufacturing LLC
Drilling microholes requires expert approach
8 | MARCH/APRIL 2010 | MICROmanufacturing
Drilling a 0.003" hole is no small task. Virtual
Industries Inc., a manufacturer of vacuum
systems, discovered this when it needed vacuum
tweezer tips capable of handling parts
as small as 100μm. Based on experience with
larger tips, the Colorado Springs, Colo.-based
company knew local machine shops would nobid
such a small tip, so it turned to its subsidiary,
Prime Axis Manufacturing LLC, also in
Colorado Springs. In the following, the author
explains, step by step, how Prime Axis solved
the problem.—Ed.
To produce vacuum tweezer tips, we not
only needed 0.003"-dia. carbide microdrills,
which only a limited number of toolmakers
produce, but also ones with a 0.040"
flute length. The toolmaker we were buying
The hole diameter is 0.003".
The flat across
the top is 0.008".
from, however, stopped offering drills that size
as a standard item and required a minimum
order of 100 drills to produce them as specials.
That meant spending about $7, 000 on drills at
the time, which we didn’t want to do.
Fortunately, Harvey Tool Co. LLC, Rowley,
Mass., began offering 0.003"-dia. drill bits
with the appropriate flute length as an offthe-shelf
item, so we used those. The drills
are uncoated.
Material selection
We considered several different materials
for the tip—brass, Torlon plastic and electrostatic-dissipative
(ESD) Delrin plastic—and
evaluated their characteristics to select the
one that would satisfy Virtual Industries’ customer
base.
We determined the fibers used in the fabrication
of Torlon tended to redirect the
0.003"-dia. drill bit, causing tool breakage,
which eliminated that choice. Brass is easy
to machine but might physically damage the
delicate parts a tweezer tip handles, so it was
also eliminated.
The ESD Delrin seemed like the logical
choice. It has a surface resistivity of 10 8
to 10 10 ohms and bleeds off any buildup
of electrostatic charge. That is a concern
when handling microparts, because it only
takes a few electron volts to cause a part
to stick to the tip and not release. In
addition, an electrostatic charge can damage
electrical and microcircuitry components.
Delrin is also soft, so it will not physically
damage parts.
Although we knew the material’s characteristics
were appropriate, we experienced a
problem with tool breakage because the center
of the ESD Delrin bar stock—where the
hole is drilled—has a lot of porosity as a result
of how it’s produced. Every few parts
the drill would hit a small pore, which would
cause the tool to break. After spending time
adjusting the feeds and still breaking several
hundred dollars worth of drills, I located a
supplier for Delrin with much lower porosity
and overcame the problem.
All images: Prime Axis Manufacturing
A vacuum tweezer tip from Virtual Industries
required Prime Axis Manufacturing to drill a
0.003"-dia. hole in electrostatic dissipative Delrin
plastic. continued on page 11