Preventive Maintenance on a Worn Lathe
A centre lathe in a training workshop has developed three symptoms in the same week: a faint rhythmic vibration visible on the finished surface, a slight taper on work that should be parallel, and a growing oil film under the headstock. The maintenance log shows the last lubrication check was four months ago, the apron oil level is at the minimum mark, and the bed ways near the headstock look polished and dry compared with the rest of the bed. The lathe is booked for a student exercise at 08:00 tomorrow. The workshop supervisor wants to top up the oil and run the exercise.
1. Rank the three symptoms by likely cause and urgency, and justify the ranking.
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1. Dry, polished bed ways near the headstock - highest urgency. Polished, dry ways mean metal-to-metal contact and loss of the oil film exactly where load is greatest. Wear here is progressive and irreversible, and it directly explains the taper: as the saddle moves along a worn region, the tool height and alignment change, cutting a taper on work that should be parallel. This must be corrected before any further cutting.
2. Oil film under the headstock - next. A leak may be a loose drain plug, a failed gasket or a worn seal. It lowers the oil level, which threatens the spindle bearings and gears. Left alone it leads to heat, noise and eventual bearing failure. It is urgent but not immediately destructive if the level is restored and the cause found.
3. Rhythmic vibration - investigate alongside. It points to a rotating-element fault: a damaged gear tooth, a worn belt joint, a loose chuck or an unbalanced workpiece. It may be a symptom of the same lubrication neglect rather than an independent fault.
All three are consistent with four months without a proper lubrication check, so the root cause is the lapsed maintenance routine, not three separate faults.
2. Respond to the supervisor's proposal to top up the oil and run the exercise.
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Topping up and running is unsafe and uneconomic. Adding oil does not undo wear, and running a student exercise on dry, polished ways will accelerate that wear and produce scrap work with a taper. The leak will also continue, so the level will fall again during the session.
Recommended response:
- Cancel or relocate tomorrow's exercise; the lathe is not fit for acceptance work until checked.
- Clean the ways, inspect for scoring and check lubrication flow to the saddle and apron before running.
- Find and fix the leak - inspect the headstock gasket, plugs and seals - then refill to the correct grade and level.
- Check the spindle for play and temperature rise after a short no-load run, and check the chuck mounting for the vibration source.
- If a taper persists after lubrication and alignment checks, measure it with a test bar and correct by adjusting the tailstock or, if the bed is worn, restrict the machine to roughing until it is reconditioned.
- Record all of this in the maintenance log and restore a defined lubrication interval, since the four-month gap is the underlying failure.