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The Care and Feeding of your CMM

Your coordinate measuring machine should run trouble-free year in, year out, interspersed only with an annual calibration and Preventative Maintenance (PM) visit; when it doesn't, there are generally good reasons for it.

Location

Should the machine be placed on the shop floor or enclosed in a lab? Maintenance costs will be higher if the machine is placed on the shop floor, but often the convenience might be worth it. Some machines are better suited to shop floor use than others; hard bearing machines, for instance, excel on the shop floor. Inspection on the shop floor is a growing trend and provided the guidelines outlined below are followed, maintenance costs will be minimized.

Air Supply

20% of all breakdowns and maintenance costs are caused by poor air quality. A refrigerant air dryer is recommended on all air bearing machines regardless of the machine’s location.

In most factories, the coordinate measuring machine uses the shop air supply and, generally speaking, those lines run just under the plant ceiling. In the summer, condensation occurs within the air lines and water permeates the CMM which damages the bearings and short-circuits the electronics. Maintenance people sometimes have a habit of putting oil in the air supply.

This works well on machine tools, but kills coordinate measuring machines! Moisture and oil in the air lines cause degeneration of the internal piping and blockage of the air bearings. Important note: Collapsed bearings cause big troubles!

Electrical Supply

Show me a machine that has chronic service problems and, generally speaking, the issues can be traced back to power supply problems. It's amazing how companies will spend many thousands of dollars on a new coordinate measuring machine yet will not invest in a power conditioner/battery backup system. It's not just the fluctuation of current that causes problems, but also noise transmitted through machine tools operating on the same circuit.

Remember, the coordinate measuring machine is not like a machine tool and its controller is much more sensitive to the variability introduced by shop electricity.

Cleaning

Cleaning is the biggest single issue governing the reliability of your coordinate measuring machine, and even more so with the machine that is not in the lab. The bearing ways on many of the new brands of CMMs are exposed, therefore it’s important that these ways are wiped clean daily or, at the very least, weekly.

Small particles can easily get under the air bearings and score the ways. On most bridge machines the slave leg runs on the surface plate or a beam, so it is a good idea to clean this area several times a day. Dirt and metal particles have a tendency to embed themselves under the bridge bearings which causes precision issues and possibly motor drive problems later on.

When scales are exposed it's also important to gently wipe them down with isopropyl or methyl hydrate and we emphasize the word GENTLY!

Controller and Computer Air Filters

Controller and computer filters should be checked weekly and replaced if necessary. A large customer of ours who had three shop floor machines couldn't understand why all three machines had controller overheating problems and eventual shutdown.

On inspecting the controllers our service crew found the air filters were clogged. We replaced the filters and the controllers are now working fine. The customer now has the maintenance department check these filters weekly and replace when required.

Preventative Maintenance (PM) Visits. During the annual calibration, don’t forget to ask the service company to do a preventative maintenance check. This should include:

  • Visual inspection of bearing conditions
  • A check of all filters
  • Inspection of drive components
  • Verification of encoder gaps
  • A good cleaning of the machine if time permits

Summary

I understand that everyone is extremely busy, however, a few minutes daily or weekly spent on maintaining your coordinate measuring machine can save you thousands of dollars down the road. If you are unsure what applies to your machine, I recommend you ask your service provider to come over and explain basic maintenance for you. To schedule a preventative maintenance check, please visit the service and repair section of our website.

Feedback

We want your feedback! Are you allocating enough time to properly maintaining your CMM? Have you established a formal CMM maintenance procedure as part of your quality sysem? Do you have a horror story of unnecessary repair and maintenance costs?  Let us know!

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