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Why older CMM drive systems still work brilliantly, if you understand them properly
One of the easiest mistakes to make with an older coordinate measuring machine (CMM) is assuming that older automatically means worse.
In reality, many older CMM designs are mechanically excellent. Different to modern systems, certainly. Sometimes noisier and occasionally more agricultural than today’s ultra-clean drive arrangements, but often remarkably robust and reliable when they are understood and maintained properly.
A CMM does not become unsuitable simply because newer drive technology has entered the market. What matters is the condition of the machine, how its mechanical systems are performing and, ultimately, whether it continues to deliver the measurement performance required of it.
A recent machine inspection provided a good example.
A Simple but Effective Mechanical Drive System
The primary Y-axis on this particular CMM uses a smooth steel drive bar with a ‘V’ pulley and pinch roller arrangement to transfer movement across the axis.
Compared with newer drive systems, it is a very physical piece of engineering. You can see how the machine is transmitting force through the drive system rather than having everything concealed within assemblies and electronics, and there is something refreshingly straightforward about that.
The motor transfers drive through a flat belt onto an intermediate pulley before driving the main ‘V’ pulley assembly against the steel drive bar itself. Contact between the pulley and drive bar provides the traction required to move the axis.
It is mechanically simple, but that simplicity shouldn’t be confused with poor engineering. When the pulley, belt, roller and drive-bar surfaces are maintained correctly, the arrangement provides stable, controlled movement across the machine axis.
Most importantly, on the machine we inspected, it was still working exactly as intended.
What Are We Actually Looking for During an Inspection?
Looking at an older drive system isn’t simply a case of checking whether the machine moves when commanded. The condition of the individual mechanical elements, and how they interact, tells us a lot about how the system is behaving.
During this inspection, all of the drive components remained in good operational condition, and the correct belt tension had been maintained. There was no evidence of drive slip, and the axis remained stable during movement and positioning checks.
Deterioration within a mechanical drive arrangement can show itself through changes in traction, movement or positioning behaviour, so these are all things we look for when assessing the overall condition of the system.
In this case, there was no immediate operational problem, although there was something worth noting for the future.
Reading the Wear Before It Becomes a Problem
Early wear lines were beginning to appear on the steel drive bar at the pulley contact points. These are essentially witness marks created over time as the same contact surfaces interact during repeated machine movement.
Their presence doesn’t automatically mean the drive bar has failed or requires replacement. Instead, they provide useful evidence of how the component is ageing.
This is where experience with older CMM systems becomes particularly valuable. An engineer needs to distinguish between normal evidence of use, developing wear that should be monitored and deterioration that has begun to affect performance.
Replacing a component simply because it shows signs of use can be unnecessary, but progressive wear shouldn’t be ignored until it causes a problem. The important thing is recognising what you’re looking at and knowing when intervention is actually required.
Sometimes the Best Solution Is the Simplest One
If wear on this particular drive bar eventually begins to affect traction, the component does not necessarily need to be replaced.
The existing steel drive bar can be rotated slightly, presenting a fresh contact surface to the pulley arrangement and moving the established wear points away from the primary contact area. This allows the existing component to remain in service for longer.
It is a straightforward and proportionate engineering solution, based on understanding how the original mechanical system was designed to work.
This type of knowledge can be particularly valuable when maintaining legacy CMM equipment, where replacement components may be increasingly difficult or expensive to source. Understanding the machine can often reveal a much simpler solution than automatically replacing a serviceable part.
Preventative Maintenance Is About Knowing When to Intervene
Good preventative maintenance doesn’t mean replacing every component that displays visible signs of age. It means understanding the condition of the machine, identifying developing issues and taking appropriate action before they become problems.
On a mechanical drive system, belt tension, component condition, traction, movement and developing wear all contribute to the overall picture. Looking at these elements together allows an engineer to assess how the system is behaving rather than making a decision based purely on the age or appearance of one component.
That experience matters particularly with older machines. Modern diagnostics can tell us a great deal, but there is still considerable value in understanding the mechanical principles behind a CMM, knowing what normal wear looks like and recognising when something has genuinely changed.
Not Every Machine Needs the Latest Drive Technology
Modern CMMs offer significant advances in speed, control and overall capability, but that doesn’t suddenly make every older drive arrangement obsolete.
Many established CMMs continue to provide stable, reliable service, particularly in applications where outright speed is less important than repeatability, reliability and maintaining an established measurement capability.
For some manufacturers, an older CMM may already be integrated into a proven inspection process. Operators understand it, measurement routines are established, and the machine’s behaviour is known. Replacing that equipment purely because of its age can therefore be difficult to justify if its condition and verified measurement performance remain suitable for the application.
The decision should be based on capability and condition rather than the date on the machine’s nameplate.
Of course, a mechanically sound drive system alone does not prove that a CMM is measuring accurately. Appropriate machine verification and calibration are still required to establish the performance of the complete measurement system. But from a mechanical maintenance perspective, understanding what is normal, what needs monitoring and what genuinely requires intervention can help keep an established machine operating reliably.
Understanding the Machine Changes the Maintenance Decision
Back on this particular CMM, there was nothing dramatic to report. The drive components remained in good condition, belt tension was correct, there was no drive slip and axis movement and positioning remained stable.
The early wear lines on the steel drive bar were worth recording and monitoring, but they did not justify unnecessary replacement. If the wear eventually progresses to the point where traction begins to be affected, rotating the drive bar can provide a fresh contact surface and extend its useful life.
Nothing complicated, nothing failing and nothing requiring immediate replacement. Just a well-maintained mechanical system continuing to do the job it was designed to do.
That is perhaps the wider lesson from this particular machine. Not every successful engineering solution needs replacing simply because something newer exists. Quite often, the smarter approach is understanding how the original system works, maintaining it correctly and knowing when intervention is actually necessary.
A surprising amount of precision engineering still depends on relatively simple mechanical principles that were solved very well the first time around.
Need Support with an Existing CMM?
An ageing CMM doesn’t automatically need replacing. Understanding its mechanical condition, measurement requirements and future support needs can help determine whether maintenance, repair, upgrade or replacement is the most appropriate route.
Measurement Solutions supports manufacturers with CMM service, maintenance and upgrade requirements, helping organisations get the best from both established and modern measurement equipment.
Talk to our team about the condition and future requirements of your CMM.
