Page 5 - Summer 2024

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TECHTIPS • SUMMER 2024

ARE YOU

GETTING

THE POINT?
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BY ROGER KERN
PRINCIPAL CONSULTANT
INTERNATIONAL TECHNOLOGY PROFESSIONALS

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The key to reliable threading in a Wire EDM is the condition of the free end of the
wire that we are attempting to thread. This treatise will explore the various methods
(and the consequences of those methods) for preparing the wire end for both
automatic and manual threading.

There are numerous instances where clients have con-
AWT WIRE END PREPARATION
tacted me complaining that they are having threading
issues due to the fact that their EDM wire is oversize.
threading issues, let’s briefl y examine the wire end
Invariably, after measuring a sample of the wire they Before we get into the details of the causes of wire
preparations employed by machines that automatically
send me on my laser micrometer (which is accurate
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thread the wire.
to four millionths of an inch and regularly calibrated to
standards traceable to NIST), I determine that the wire is
not oversize. Thus, an oversize wire is not the cause of
EARLY AWT
their reported threading issues.
Many years ago, Charmilles (which was one of the
pioneers in Wire EDM) utilized a strategy of heating and
WIRE AND WIRE GUIDE DIMENSIONS
stretching the wire to both straighten it as well as reduce
AND TOLERANCES
was cut with a cutter just before the water jet assisted
threading operation commenced. Even if the cutter
Before delving further into the threading issue, we need
to examine the industry standards for wire and wire its diameter. After the heating and stretching, the wire
produced a small burr, it was not an issue because the
guide dimensions. The industry standard tolerance for
stretched wire was undersize by more than the amount
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of any burr.
wire diameter is +0/-2μ (+0/-.00008”). The typical indus-
try standard for regular wire guides is 5μ (.0002”) over
the nominal wire size. (Please note for some applica-
tions and machines that amount is greater and for “high
CURRENT AWT
precision” guides that amount is less.) I have not been
able to determine an industry standard for the actual
Virtually all modern Wire EDM’s utilize a similar,
tolerance on the guide oversize.
but greatly refi ned wire end preparation strategy.
The wire is still heated and stretched, but is often
Based upon these numbers, there should be a total
cooled while stretched for superior straightness that
diametral clearance between the wire and the guide of
allows for both jetted and jetless threading. In addition,
approximately two “tenths.”
modern machines use a thermal cutting process
which requires less maintenance and produces a
So, with a wire that is not oversized and .0002” clear-
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EDM Today Magazine EDM Today Magazine EDM Today, Summer 2024 Issue
wire tip without a burr.
ance, why should there ever be wire threading issues?
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