Since small hole drilling is becoming more popular for
production applications in aerospace, medical, electronics, and other sectors
that require very small, extremely accurate holes with good surface finish,
Makino is seeing a growing demand for machines that can produce these holes
consistently and repeatably. Here are some test results that were produced by
the Makino EDM Applications Department in Auburn Hills, MI.
The Applications Department performed this test to
prove the repeatable accuracy of the EDGE2 Fine Hole machine. A series of 15
holes, 0.010" (0.254mm) diameter, was made on the machine using 0.008" (0.203mm)
diameter copper pipe to predrill each hole, then a solid copper rod was used for
finishing. The holes were measured for entrance and exit size, and also shape
accuracy on an OGP Quest Vision System.
There are several factors that
determine the accuracy and speed at which the 0.010" (0.254mm)
diameter holes can be produced. When the 0.008"
(0.203mm) diameter copper tube is
at full length, the machining time is longer and a greater taper is produced
from entrance to exit for the solid finishing rod to remove. This is indicated
by the values shown for holes 1 through 9. As the roughing pipe electrode
becomes shorter, the machining speed and break-through at the bottom of the
holes are much faster. The roughing process produced a slight taper of 2 ~ 4
tenths (5-11 micron) which was removed during the finishing process. It was
critical to perform these tests in a climate controlled room, and to use only
the highest quality copper tubes available to reach these results and times. To
maintain the better results shown in holes 10 through 15, the electrodes should
be purchased in a maximum of 6.0” lengths. All 15 holes where roughed and
finished in approximately 60 minutes for an average of 4 minutes to include
dressing between holes.
Hole #
Entrance Exit Difference
1 0.010032” 0.010432”
0.000400”
2
0.010090” 0.010242” 0.000152”
3 0.009993” 0.010127”
0.000134”
4
0.010033” 0.010131” 0.000098”
5 0.010048” 0.010145”
0.000097”
6
0.010040” 0.010320” 0.000280”
7 0.010065” 0.010569”
0.000504”
8
0.010025” 0.010348” 0.000323”
9 0.009994” 0.010336”
0.000342”
10
0.009962” 0.010039” 0.000077”
11 0.009966” 0.009984”
0.000018”
12
0.009956” 0.010038” 0.000082”
13 0.010052” 0.010064”
0.000012”
14
0.010056” 0.010066” 0.000010”
15 0.009996” 0.010004”
0.000008”
Cpk Results of Entrances
Based on specific pre-defined
requirements for these holes, Cpk is 1.82.
This Cpk is considered
exceptional based on the following scale:
0 to less than 1.0 is
unacceptable - sometimes called "not capable"
Greater than 1 to 1.33
is fair
Greater than 1.33 to 1.66 is acceptable
Greater
than 1.66 is exceptional
These
Cpk values and ratings are per QualityAdvisor.com
Hole Shape and Location

The holes shown above were photographed
at 166x magnification on the OGP Quest Vision System. Pitch between center of
holes was programmed at 0.0250” (0.635mm)

The two photos shown above were taken
at 403 magnification. Back light shown at left, surface and back light shown
at right.
For more information on these test
results or the Makino Edge2 Fine Hole EDM machine, send an email to bill.paul@makino.com.