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How machine maintenance affects safety

The primary reason companies perform preventive maintenance on their production equipment is to minimize, if not eliminate, unpredicted downtime. If a potential problem is corrected before it causes a component on the machine to fail, of course, the component will not fail. Most manufacturing people would agree that if you’re doing your preventive maintenance properly, your machines should never go down for corrective maintenance – at least not due to a component failure.


There is a second, safety-related benefit to properly maintaining your machines. Well maintained machines are safe machines to run. Keeping machines properly maintained provides a safe environment for your setup people and operators.


An obvious comparison can be made to operating an automobile. Think of all the components in a car that are related to safety. You wouldn’t drive a car if you suspected problems with the brakes, would you? Yet I’ve seen companies that allow machines to continue running even with safety-related maintenance issues. Here are a few examples:

  • Failed indicator lights – Most CNC machines have several indicator lights. Many are related to the control panel buttons and switches. When a button is pressed, a light comes on (or goes off) to indicate the condition of the function that the button is used to activate. If the light is burnt out, of course, the operator won’t be able to tell whether or not the function is activated.

  • Failed (or disabled) safety interfaces – Almost all CNC machines have built in safety interfaces to ensure that the machine will not run when something is wrong. The most common is the door interlock. The machine will not run when the door is open. I’ve seen companies that disengage this interlock – sometimes temporarily – so the setup person can see inside the machine’s work area more clearly. This places operators in a dangerous situation if the door interlock isn’t engaged once the setup is completed.

  • Running with known problems – Many companies continue using machines even when they know something is wrong. The intention is to eventually fix the problem, but the current job is very hot so they feel the machine cannot be stopped – or the needed component isn’t available yet. This may be acceptable if there are no safety-related issues, and if there is no possibility of further damaging the machine. But I’ve seen very questionable decisions in this regard. In one company I know of, the tool changer mechanism was intermittently dropping tools from its magazine. A person was actually assigned to stand under the magazine to try to catch falling tools in a padded box – a very dangerous assignment indeed.

  • Failure to perform preventive maintenance – If any needed preventive maintenance task isn’t done, something on the machine will eventually fail. Consider the safety-related implications of random failing components. People will be in a constant state of danger. Again, compare this to driving a car. If you never perform maintenance on the car (fluids, filters, tires, brakes, etc.), something will eventually fail. Would you want to be the one driving the car when it does? While you’d never consider treating a car in this manner, I’m amazed at how many companies have a “run it ‘till it breaks” attitude about their CNC machines.

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