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In precision manufacturing, especially with wire EDM, the question is no longer “Can the machine move?” but rather “Can it move exactly where you tell it to, and do that over and over again?”

Two core performance metrics answer this question:

Positioning Accuracy and Repeatability.

They are fundamental to whether your finished parts match your design consistently, across every shift and every batch.

1. Positioning Accuracy: Can the Machine Hit the Mark?

Many users focus on how fast a machine cuts, or how smooth the surface looks. But before any of that matters, your machine must reach the correct position with precision.

What is positioning accuracy?

It’s how close the machine actually gets to the coordinates you programmed.

For example, if you command the machine to go to 50.000 mm, and it stops at 50.002 mm, that’s a 2-micron error.

In wire EDM, an accuracy of ±2 microns or better is considered excellent.

What does it depend on?

The ball screw and servo motor resolution and responsiveness

The linear guideways’ geometry and friction characteristics

The mechanical assembly precision of the machine as a whole

Why does it matter?

If positioning is off, your cutouts or holes may not align with the design, leading to poor part fit, failed assemblies, or out-of-spec molds.

This is especially critical in tight-tolerance industries like tool-making, aerospace, and precision die manufacturing.

2. Repeatability: Can It Do It Again?

Good positioning is great.

But real production needs it every time. This is where repeatability comes in.

What is repeatability?

It measures how consistently the machine can return to the same point over multiple moves.

Say you command the machine to move to 30.000 mm five times. You measure each stop. If the deviation is within your acceptable range, that’s pretty high repeatability.

What affects repeatability?

The resolution of the encoder used in the motion control system

Backlash, or mechanical play, especially in the screw-nut interface

The quality of servo tuning, which controls motion smoothness and stop behavior

Why does it matter?

In mass production, repeatability ensures that every part in a batch is dimensionally identical.

Poor repeatability leads to parts that are sometimes within tolerance, sometimes not, even if the program hasn’t changed.

In mold-making, even a 3-micron deviation might cause misfit, binding, or flashing issues.

3. How to Evaluate These Metrics in a Machine

Evaluation methods include:

Laser interferometers or linear glass scales to measure absolute position and error

Repeating programmed moves (e.g., 0 to 100 mm back and forth) and recording stop points

Charting the variation to assess both absolute accuracy and consistency over time