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The electrical arc from the wire to the part needs to be controlled. If the resistance of the water is too high, the wire
will have to touch the part before the electricity will conduct to the part, which would just cause wire breaks, and/or a
short condition. If the resistance of the water is too low, the electricity from the wire will be dispersed erratically in the
work tank, taking away from energy transfer to the part, and will cause wire breaks, slow cut speeds, a bad fi nish, and
cause parts to rust quicker. With the correct water resistance, Fanuc recommends between 5 (50,000 ohms per cubic
cm) and 7 (70,000 ohms per cubic cm). Certain applications will require an even higher resistance, like cutting PCD,
Tom VanValkenburgh | EDM Service Engineer EDM Today Magazine
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or using the Micro Finish on the arc transfers from the wire to the part in a controlled fashion allowing the vaporized
particles to be fl ushed out of the way. Low resistance will also cause false reads on the detect pin during an M60
(wire thread), which can cause an immediate “reverse alarm,” and it will cause the machine to effectively erode the
brass components in the machine.
The Deionizing bottle controls the water’s resistance, by removing ion particles and raising the resistance of the water.
Some metals, like aluminum, can naturally raise the water’s resistance and is not a concern unless it raises it above
around 20 (200,000 ohms per cubic cm). The resistance can easily be lowered by adding a small amount of table salt
(a half teaspoon would be a good starting point).

616-291-4505 | Tommyvedm@outlook.com | tommyvedm.com
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EDM Support

Q: My Chmer CW322S will not power up. How can I debug this?
A: Many times, we receive a call in which the computer comes up, but the machine does not fully power up.

Many machines, like the Chmer, have safety switches on the axis to power down the machine if the axis takes off
because of a loss of feedback from the motor encoder or simply because something happens, causing it to run into the
cal limit, which could possibly damage the axis. EDM Today Magazine
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limits. The mechanical safety switches are normally past the home and limit switches.
Normally, when you home the machine, it will hit the home switch (fi rst switch) and then move slowly in the opposite
direction until it fi nds either the mark on the motor encoder or the mark on the scale. Some machines will move quickly
to get close to the home mark, then slow down to look for it.
When you move the table to the axis limit, it could simply hit a mechanical limit switch or possibly stop by the software
limit. If the axis runs past both, it will generally stop when it hits the mechanical safety switch.
When it hits the safety limit, the machine will completely power down to prevent the axis from running into the mechani-

You can see in this schematic that the safety switches are in series, so if any one of them is tripped, it breaks the circuit,
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and the machine powers down – see Figure 1.

Figure 1
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EDM Today, Fall 2024 Issue