Low Spindle Utilisation in a Machine Shop: Finding the Lost Hours

A spindle that turns for four hours of an eight hour shift is not cutting slowly. It sat still for the other four. The first job is to account for that stillness.

Feeds and speeds matter. They are a later question. Most shops find their largest loss sits between jobs, not inside them.

Ask each operator to book start and end of every state against the job card: setup, run, waiting and breakdown. Start with one week and a few machines.

Setup includes fetching the fixture, loading the offsets, touching off tools and running a first piece. On a VMC with a vise, it may be short. On a five-axis part with a dedicated fixture and a probing routine, it can take the morning.

Compare booked setup against the planned figure on the route card. A repeat part that takes twice the planned setup tells you something is missing, perhaps a fixture without a locating pin or offsets that were not saved.

Fix the repeat parts first. They return every month. Each fix pays again, and a single missing locating pin can cost a half hour on every run.

A lathe that stops because bar stock has not arrived looks like a purchasing problem. Often the cause is earlier: a job released with no check on whether the bar, the casting or the heat treated blank was in the stores.

Look at the booked waiting hours by reason. If material heads the list, check the release step. Does the planner see stock and incoming orders before sending the job to the floor?

Outside processes add another gap. Parts out for plating or heat treatment come back late and leave the next operation idle.

A new G-code programme proved on the machine ties up a spindle that could be cutting. Where possible, prove it in simulation or on the least busy machine. Record how long each proof takes so you can see the true cost of new parts.

Inspection queues grow when one inspector serves six machines. The operator waits for first piece approval with the spindle idle. Count the minutes between asking and approval, per job.

Both losses are visible once the stoppage is booked with a reason. Without a reason, they all fall into one vague bucket called downtime.

Add the booked hours by reason for each machine. Rank the causes. The top two will usually account for most of the lost time, and they differ from shop to shop.

Take the ranked list to a short Monday meeting with the planner, the tool crib and the inspector. Choose one cause and one fix. Run it for two weeks, then look at the figures again.

Software helps by capturing the bookings at the machine and totalling them, so no one compiles a sheet. Start by trialling the reason codes on a paper card for a week.