Introduction: Measuring Where It Matters Most
In modern CNC machining, accuracy is not achieved by cutting alone; it begins with knowing exactly where the workpiece sits on the table. Traditionally, that knowledge came from manual edge finders, dial indicators, and skilled operators spending long minutes setting each job. Today, the same work is done automatically, in minutes, by an on-machine probing system. At the heart of countless small and medium machining centres around the world is one of the most proven systems ever built: the genuine Renishaw OMP40-2 optical probe working with the OMI-2 receiver. This article introduces both components, explains how they work together, and outlines what they deliver in daily production.
The OMP40-2: A Compact 3D Touch-Trigger Probe
The OMP40-2 is an optical, three-dimensional touch-trigger workpiece probe designed by Renishaw for workpiece inspection and job set-up on small to medium machining centres and small multi-tasking machines. It is also a natural fit for high-speed machines fitted with small HSK or small taper spindles, where space is tight and weight matters.
Its dimensions tell the story of its design philosophy: 50 mm long with a maximum diameter of 40 mm, and a weight of 250 g including batteries (234 g without). This ultra-compact envelope allows the probe to be handled by the automatic tool changer exactly like a conventional tool, stored in the magazine, and called into the spindle on demand with no manual intervention.
Inside that small body sits a proven kinematic touch-trigger mechanism. When the stylus touches the workpiece, the mechanism deflects and triggers a signal, and the design is engineered for exceptional repeatability: 1.00 µm (40 µin) 2σ, unidirectional. In practice this means that when the probe measures the same feature repeatedly, the results agree within one micron, which is the level of confidence needed when probing routines feed offsets and inspection data directly into the machining process.
The probe senses in three directions, ±X, ±Y and +Z, using ceramic styli in lengths from 50 mm to 150 mm. Trigger force, measured with a 50 mm stylus, is 0.50 N in the XY low-force direction, 0.90 N in the XY high-force direction, and 5.85 N in Z, with stylus overtravel of ±12.5° in the XY plane and 6 mm in +Z. These modest forces protect delicate workpieces while still providing a decisive, repeatable trigger. The unit is sealed to IPX8, meaning it is protected against prolonged immersion, so coolant, oil, and swarf in a busy machine environment do not silently degrade it.
Power comes from two 1/2 AA 3.6 V lithium-thionyl chloride batteries, giving a maximum standby life of 1500 days and up to 1350 hours of continuous use, a combination that many shops find they only interrupt when changing the stylus or performing routine maintenance. The probe is switched on optically and switched off optically, or by a timer, so it wakes for a measuring cycle, does its job, and returns to sleep without human involvement.
The OMI-2: The Optical Receiver and Interface
The OMP40-2 transmits its trigger information as infrared light, and it is the OMI-2 that listens. The OMI-2 is an optical receiver and machine interface, typically mounted inside the machine enclosure on a bracket that lets its clear window face the working area. It receives the infrared pulses from the probe, decodes them, and converts them into electrical signals that the CNC control can interpret, turning the probe's trigger into a measured position in the machine coordinate system.
Because the OMP40-2 emits over a full 360° envelope, the receiver does not need to be aimed at the probe with surgical precision; opposing light cones simply need to overlap over the travel of the machine axes, and modulated transmission gives exceptional resistance to interference from arc welding, ambient light, and the flicker of other machines. The OMI-2 operates on a 15 V to 30 V DC supply and is available with standard 8 m or 15 m cables (the 8 m configuration uses a shielded 13-core cable), with the interface sealed to IPX8 for life inside a wet, oily machine. Status LEDs on the unit give operators immediate feedback on probe triggering and system health, and because the interface is an intelligent part of the chain, it also relays probe battery status so a low cell is noticed before it becomes a failure.
The OMI-2 belongs to Renishaw's new-generation receiver family, which supports both modulated and legacy transmission. This means the OMP40-2 can also work with other Renishaw receivers, just as the OMI-2 can support OMP40-2, OMP60 and OMP400 probes, giving users a degree of forward and backward compatibility that protects their investment when machines or probes are upgraded.
How the System Works in Production
In a typical cycle, the probe is stored in the tool magazine and loaded into the spindle by the automatic tool changer. On command, an optical on-switch wakes the probe, the spindle moves to a programmed position, and the probe is moved toward the workpiece. The instant the stylus touches the surface, the kinematic mechanism triggers, the probe transmits an infrared burst over its 360° envelope, and the OMI-2, sitting somewhere in the machine, receives it and signals the control. The control records the axis position at the instant of trigger and calculates the workpiece datum.
From that single basic motion, a remarkable range of functions follows. The machine can find the centre of a bore or a boss by touching four points, set the X and Y datum of a blank casting in seconds, measure the height of a feature to establish the Z datum, check a critical dimension after roughing and feed a compensation value before finishing, and even verify key features at the end of a batch. Every one of these operations happens without an operator opening the door or touching the part, and each measurement is recorded with the one-micron repeatability the system is known for.
The practical benefits are the ones that show up on the shop floor. Set-up and calibration routines shrink dramatically, returning time to cutting cycles. Workpiece alignment that once consumed an hour and a half becomes a ten-minute automated step. Because measurements are taken on the machine, with the part still clamped, dimensional drift is caught early, reducing rework, concessions, and scrap. Relying on measured positions rather than manual judgement also removes the largest source of operator variability from the process, which is why probing is a cornerstone of lights-out and unattended machining.
Why the Genuine System Matters
The words "original" or "genuine" in front of this system are not decoration. Renishaw probes are manufactured to metrology-grade standards, individually tested, and supplied with documented performance: the 1.00 µm 2σ repeatability, the trigger forces, and the sealed construction are certified characteristics, not advertising claims. Genuine units carry full traceability and are supported by official documentation, calibration guidance, stylus options, and service channels. For a component whose measurements become production data, the difference between a certified instrument and an unverified substitute is the difference between trusting one's data and guessing at it.
Installation and Maintenance in Practice
Bringing the system to life is a mechanical and electrical step, followed by a calibration step that is essential. First-article calibration typically uses a reference ring gauge and a reference tool: the probing cycle establishes the probe length offset, the effective trigger radius of the ruby stylus ball, and any concentricity deviation between the probe and the spindle axis, and the software compensates for these values automatically. Practice also matters over the system's life. The lithium battery should be replaced with the specified 1/2 AA 3.6 V lithium-thionyl chloride type, and when the probe's low-battery indicator appears, replacement should not be postponed. After every battery change or any impact, the probe should be recalibrated, because even a tiny physical shift will appear in measured data. Equally simple is keeping the optical windows of probe and receiver clean: coolant and swarf residue on the windows weakens the infrared link, so wiping them regularly protects both range and reliability.
Applications Across Industry
The OMP40-2 with the OMI-2 is the probing workhorse of small to medium machining centres, but the application list is wider. Turn-mill machines use it for part verification in the same setup, mold shops use it to align electrodes and cores, automotive and precision engineering plants use it for datum setting on complex housings, and job shops rely on it to make every next order faster than the last. Wherever a machine tool must know where its workpiece is, and must know it to within a micron, this compact Renishaw system provides the answer.
Conclusion
The genuine Renishaw OMP40-2 and OMI-2 form one of the most widely trusted probing systems in machining. A compact, sealed, battery-powered probe with one-micron repeatability, a 360° infrared link resistant to interference, and an intelligent receiver that speaks the language of the CNC control: together they turn a machining centre into a measuring machine that aligns, checks, and protects its own work. For shops that measure materials in microns and time in minutes, that is not a feature; it is the foundation of profitable precision.
About Makinopc
Makinopc is the brand of Shenzhen Makinopc Mechanical & Electrical Co., Ltd., a Chinese manufacturer specializing in CNC machine tool accessories. Established in 2014 and headquartered in Shenzhen, the company integrates research, design, and sales of automatic tool setters, measuring probes, electronic handwheels, and pulse generators, band switches, spindle encoders, and system panels for CNC machine tools. Makinopc products are compatible with major control systems including Fanuc, Mitsubishi, Fagor, Heidenhain, Syntec, LNC, and GSK, providing machining shops with dependable probing, tool setting, and manual-operation solutions backed by responsive technical support.
