Page 6 - Summer 2024

EDM Today Magazine EDM Today Magazine EDM Today Magazine

MANUAL WIRE THREADING
Threading a Broken Wire
Manual threading is still often utilized either for the mul-
As all of you have likely experienced, it is virtually
titude of older machines still out there, for jobs that are
impossible to rethread a broken wire. The reason for
not compatible with auto threading and often for start-
this is that, at the break point, the wire is both rough and
ing a new spool on an auto threading machine. (Some
machines require the wire to be successfully threaded
shown in Figure 4.
in order to create the tension required for stretching the
wire during the wire end preparation routine.) often oversize, even though it has a pointed tip as
EDM Today Magazine EDM Today Magazine EDM Today Magazine
Thus, it is during this manual threading operation that
operators often have issues with the wire not passing
Figure 4
through the guides.
Let’s examine the possible causes:
This is why machines with AWT will retract the broken tip,
This is why machines with AWT will retract the broken tip,
cut it off and create a new end by heating and stretching
Wire End Cut with a Mechanical Cutter
before attempting a rethread.
There is no practical way to mechanically cut the wire
without either distorting its diameter and/or creating
a burr. Figure 1 is a 100X image of a wire end that has
been cut with a fi ne scissor. Even though there appears A Time Out is Called
do be a clean cut, careful examination of the image Any of you who either have or have
EDM Today Magazine EDM Today Magazine EDM Today Magazine
reveals a small burr that is large enough to impede
seen early generations of Charmilles
passage of the wire through the guide. Wire cutters or
machines may have noticed some odd
nail clippers often leave a more substantial burr.
hardware on the upper front panel of the
machine as shown in Figure 5.

Figure 1

Cutting the Wire with a Lighter Flame
Most folks utilize a lighter to create a wire tip without a Figure 5 TECHTIPS
EDM Today Magazine EDM Today Magazine EDM Today Magazine
burr. While this method can be effective, the exact details
of this allegedly simple procedure matter greatly, as
simply melting the wire with the fl ame will often produce
a bulged end that is oversize as shown in Figure 2.
This odd bit of hardware is actually a very clever wire end
This odd bit of hardware is actually a very clever wire end
preparation device. It consists of two grooved copper
tungsten pins that are ten inches apart. These pins are
connected to a low voltage transformer that produc-
es about eight volts. To prepare the wire for manual
threading, one merely lays the wire over the two pins and
threading, one merely lays the wire over the two pins and
Figure 2
stretches it. The left pin is mounted on an ingenious heat
shield that concentrates the heat at the left end of the
In order to avoid this situation, it is necessary to put the
wire assuring that it will part there. (See Figure 6)
wire under tension and wave the fl ame longitudinally stretches it. The left pin is mounted on an ingenious heat
EDM Today Magazine EDM Today Magazine EDM Today Magazine
over a short distance to simultaneously part and stretch
The result is a
the wire. I have found the best way to do this is to lay a
straight length
steel block on top of the wire, pinching it between the
of wire that is re-
block surface and the machine table while pulling on the
duced in diameter
free end. Heating and stretching the wire will produce a
at the left end,
tip like the one shown in Figure 3.
that end having a
tapered tip. This
device is conve-
niently located
Figure 6
near the wire path
Figure 3 and requires no lighter or weighted block. My lab ma-
chine has this and I use it all the time.
EDM Today Magazine EDM Today Magazine EDM Today Magazine
The resulting tip will thread easily since it is both under-
The Time Out Has Expired
sized and tapered.
(Continued on next page)
65
EDM Today, Summer 2024 Issue