Linear Motors vs Ball Screw in EDM

EDM is not about speed.
EDM is about gap control.
Gap control requires dynamic accuracy.
Dynamic accuracy requires linear motors.

Linear Motors vs Ball Screw Drives in EDM - COMPARISON

Linear motors provide higher speed.
But the EDM process is slow.

What are the advantages of linear motors vs ball screw in EDM?
This comparison breaks down the real differences between these two motion systems in both Sinker and Wire EDMs and explains why flat rigid linear motor technology is built to outperform in today’s hi-precision and hi-demand production environments.

What are Linear Motors in Electric Discharge Machines for?

For the EDM process, it is not the speed itself that is important, but the accuracy and response speed of the drives.
More precisely, the kinematic accuracy multiplied by the responsiveness or what can called dynamic accuracy.
And here flat (planar) linear motor drives are beyond any competition!

Why speed is NOT the key factor in EDM?

Electrical Discharge Machining (EDM) is fundamentally different from conventional machining processes. Unlike milling or turning, where the cutting tool is in direct contact with the workpiece, EDM removes material through controlled electrical discharges across a microscopic gap between the electrode and the workpiece. Because of this, EDM is not a positioning process — it is a gap-control process.

Maintaining a stable spark gap is the key to successful EDM machining. During cutting, the distance between the electrode and the workpiece must be continuously adjusted in response to thousands of electrical discharges occurring every second. Even extremely small deviations in this gap — often measured in microns — can immediately affect machining stability, surface quality, cutting speed, and geometric accuracy.

For this reason, the servo drive system of an EDM machine must be capable of extremely fast and precise micro-movements. The machine must constantly respond to changes in spark conditions, maintaining the optimal gap with minimal delay. This requirement places unique demands on the axis drive system.

Traditional EDM machines typically use ball-screw drives, where rotary motion from a servo motor is converted into linear movement through a screw and nut mechanism. While ball screws can provide acceptable positioning accuracy in many conventional machine tools, they inherently involve mechanical transmission elements such as bearings, couplings, and preloaded screw assemblies. These components introduce elastic deformation, friction, and small internal clearances that inevitably reduce the responsiveness of the system during rapid micro-corrections.

In contrast, linear motor drives eliminate mechanical transmission entirely. The axis is driven directly by electromagnetic force, allowing the machine to respond instantly to servo commands without backlash, torsional elasticity, or mechanical lag. This direct-drive architecture provides extremely fast dynamic response, which is crucial for maintaining a stable spark gap during EDM machining.

As a result, modern high-precision EDM machines increasingly rely on linear motor technology to achieve superior surface quality, higher machining stability, and more accurate geometry. In the sections below, we examine in detail how ball-screw drives and linear motors differ, and why linear motor technology has become the preferred solution for advanced EDM systems.

EDM accuracy is a dynamic accuracy, not a positioning accuracy.

Ball screw drive
with belt reducer
of a Swiss EDM.

The two main parts of a Sodick linear motor (LM):
block of electromagnetic (EM) coils
and a panel of permanent rare earth NeFeB magnets.

For the EDM process, it is not the speed that is important, but the dynamic accuracy

In ball-screw-driven EDM machines, limitations in servo response prevent stable maintenance of the optimal spark gap. Consequently, the process operates under approximated conditions, leading to inherently lower cutting efficiency, accuracy and surface quality

The spark gap must be controlled continuously

What is required from the drive of the EDM first of all? Let's figure it out:

Ideally, for a high-quality and productive EDM process, the drive should correct the gap tens of times per second, positioning the electrode with an accuracy of microns or even more precisely.

Can conventional drives with ball screws do this with that accuracy, if even in the best of them the gap (and, accordingly, backlash!) is at least 4 microns? And if in a drive with a ball screw, to reduce the cost, there is also a belt or gear reducer?

The EDM process in many cases is a sequence of micro-movements.
In Die-Sinking EDMing, micro-movementss are required for the so-called orbital oscillations,
and often for electrode relaxations.

Linear Motors vs Ball Screw Drives
In Wire-Cut EDMing, tracing and cutting any complex curvilinear contour is a chain of micro-movements.

Linear Motors vs Ball Screw Drives in Wire-Cut EDM:
Can a ball-screw drive reliably execute 1–2 µm micro-movements
if its internal clearances and backlash are already several microns?

Comparison: Ball Screw vs Linear Motor in EDM

Why ball-screw drives cannot maintain a stable EDM gap

Ball screw = elastic mechanical transmission
Elastic transmission = delayed servo reaction
Delayed reaction = unstable gap
Unstable gap = geometry errors

Ball-screw drives rely on a complex multi-stage conversion of energy — from rotary motion to linear motion — which inevitably introduces backlash, dead zones and delayed servo response.

command impulse

interaction energy
of magnetic fields

rotation of the motor rotor

(functioning of a belt
or gear reducer, if any)

ball-screw rotation

ball-screw backlash play

linear movement
(ball-screw movement)

A long distance from a command to execution!

Ball Screw Drives – this means invariably low dynamics, a delay from the moment of power application to the start of movement.

There is a long delay from the command pulse to the start of movement at the start and each reverse. And if in such a drive there are also reductors (belt or gear), then the delays grows almost into idle time-outs:

An EDM machine with ball screws practically never operates with an optimal gaps; the machining conditions are approximated, with constant losses of speed and quality.

Why flat (planar) linear motors solve the problem

Linear drives with flat (planar) linear motors are an extremely simple construction with non-contact transmission of force, a direct drive without any kinematic chain for converting energy into motion and rotational motion into linear motion, without backlash, dead zone and uneven bumpy feeds. In fact, the moving part of a linear motor is also a mover. All that happens when processing each motion is:

command impulse

interaction energy
of magnetic fields

linear motion

And it’s all!
Barely moments from a command to execution!

Simply put:

impulse

⇓

energy

⇓

motion

Sodick Flat Linear Motors

correct the gap up to
1000 times per sec
with feedback response
in linear EDMs of up to 1 µsec
and linear scales resolution of
10 nanometers or 5 nm).

EDM is not a positioning process.

EDM is a gap-control process.

The backlashes “crawl out” at each start, reverse and stop of movement. A reminder: backlash in ball screw drives exacerbate elastic deformations, thermal deformations, kinematic errors of drive parts – losses from friction, twisting of the ball screw screw. You may object that, they say, this is nonsense, but it is precisely this nonsense, which is called microns, that we catch with our EDMs! The efficiency of ball screws, although higher than that of other mechanisms for converting rotational motion into translational motion, reaches 90% at best. But it’s not 100%!

Linear drives are direct drives free from all ball screw defects. In linear drives, multi-stage conversion of energy into motion is excluded, any factors for the occurrence of backlash and uneven feeds are excluded. Sodick linear actuators are capable of adjusting the gap up to 1000 times per second with a feedback of 10 nanometers. The result: optimal clearance at virtually any point in the EDM process, consistently optimal operating conditions, stable maximum removal, high EDM performance and surface quality!