Preventive Maintenance

Preventive maintenance is the oldest formal maintenance strategy and the first one a small shop should set up. The idea is simple: most equipment failures happen because a known wear part finally gave out, and most of those parts give out around the same interval if you know what to look for. Service the part before that interval and the failure does not happen. Skip the interval and the failure shows up at the worst possible time, usually mid run on a Friday afternoon.

"Five planned hours on a Wednesday beats five unplanned hours on a Friday."

How preventive maintenance works

A preventive maintenance program starts with a list. For each machine in the shop, write down what is on it: motors, bearings, belts, filters, hydraulic lines, electrical contactors, sensors, lubrication points. Then, for each of those parts, write down what wears, how often, and what the early warning signs are. The result is a master task list per machine.

Each task gets an interval. Some are calendar driven: change the air filter every quarter. Some are usage driven: replace the cutting fluid every 500 hours. Some are condition driven, which is where preventive maintenance starts to overlap with predictive maintenance. The interval starts as a best guess from the manufacturer's documentation and gets refined by what the shop actually finds. If the air filter is still clean every quarter, push the interval to six months. If the hydraulic lines are seeping at 1,500 hours, pull the inspection in.

The schedule lives somewhere everyone can see. In a small shop that is usually a whiteboard, a printed calendar, or a basic CMMS. The maintenance lead walks the schedule weekly, books the time, and pulls the operator in when their machine needs an hour of downtime. Findings get logged: what was inspected, what was replaced, what looked off. That log is the engine that tunes the program over the next year.

Where preventive maintenance fits on the shop floor

Picture a 15 person CNC job shop with eight machines, mostly mills and a couple of lathes. The shop has been running on a "fix it when it breaks" model. Breakdowns hit roughly once a week, and each one costs four to twelve hours of recovery plus an emergency parts order. The owner has been told to "set up PM" but does not know where to start.

A practical PM rollout starts with the two machines that have broken most often in the past year. Pull the manuals. Build a one page task list for each, with monthly, quarterly, and annual buckets. Book the first round during the next slow week. Do the work, log what was found, and use the findings to refine the next round. After two months on those machines, expand to the rest of the shop, one machine per week. By the end of the quarter, the shop has a calendar and a binder. By the end of the year, breakdowns are down to one a month and almost always on the parts the shop has not gotten to yet. That is the trade preventive maintenance offers.

Common mistakes with preventive maintenance

• Copying the manufacturer's schedule and never adjusting it. The manufacturer wrote that schedule for the worst case. Your shop is not the worst case. Tune intervals based on what you find.
• Doing PM tasks without a log. Without a log there is no learning, and the program decays into a checkbox exercise the third time the maintenance lead changes.
• Booking PM only when the shop is slow. PM that only happens when there is nothing else to do is not a program. Schedule the time and protect it.
• Mixing PM with breakdown response. The same person doing both will always prioritize the breakdown and never get to the PM. Carve PM time out separately.
• Running PM without autonomous maintenance. Most of what PM catches, operators could catch first if they were trained to look. PM should be the deeper second layer, not the only layer.

Preventive maintenance and related Lean tools

Preventive maintenance is a subset of planned maintenance and is usually paired with autonomous maintenance so the daily inspection layer catches what the monthly PM schedule does not. Its data driven cousin is predictive maintenance, which uses sensor signals instead of a calendar. PM exists in opposition to breakdown maintenance, the "fix it when it dies" default that PM replaces.