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Tag: preventive maintenance

Why your ballscrew is noisy but the pitch reads fine

Posted on by Codeller

Every month we get a call that starts with the same sentence: the pitch is still in spec, but it sounds wrong under load. Nine times out of ten the noise is not the lead. It is the recirculation.

What the numbers hide

A laser interferometer measures positional accuracy along the axis. It tells you nothing about the return path inside the nut, where the balls swap lanes. Once a return channel starts to score, the balls no longer roll cleanly. You get audible tick, a temperature rise after twenty minutes of continuous cutting, and a small but stubborn increase in following error at rapid.

What to check before you condemn the screw

  • Take a listen at idle rapid, both directions. A one-sided rumble is a strong tell.
  • Log axis load over a two-hour production run. A creeping baseline points at the nut, not the drive.
  • Pull the wiper covers and look for grease that has gone chalky rather than glossy. Chalky means it has been running hot.

Ballbar readings looked fine. Vibration analysis flagged the Y axis inside a week. That was the nut, not the screw.

If it is caught early, a nut-only rebuild is a two-day turnaround and a fraction of the cost of a full screw and support-bearing pack. Left running, you are on borrowed time before it seizes mid-cycle.

Case study: bringing a 15-year-old YLM back into cycle time spec

Posted on by Codeller

The customer bought this YLM new. It had been on continuous shift work for 15 years cutting mid-run production parts. Nothing had failed. The problem was subtler: cycle time on the reference part had crept from 3:12 to 3:55 over three years and management wanted to know why.

What we found

  • Rapid rates on X and Y were down to 32 m/min from the rated 40. Servo tune had drifted with age.
  • The tool magazine was firing slower than spec. Air pressure at the ATC was at 4.9 bar, not the required 6.
  • Spindle warm-up was taking 40% longer to hit thermal equilibrium. Cooler had a slow leak.

What we did

No parts were failing, so nothing needed replacing outright. The job was tuning:

  1. Rebalanced the servo loops on X, Y and Z. Restored rapids to spec without going near the mechanical side.
  2. Replaced the ATC solenoid and repaired the air supply line. ATC time down from 4.1 s to 2.6 s per tool.
  3. Recharged the spindle cooler and replaced the flow switch. Warm-up back to under 20 minutes.

Result

Cycle time on the reference part came back to 3:16, four seconds off the day-one figure. On a run of 800 parts a shift, that is 27 minutes of recovered production per shift. Two shifts a day, 240 shifts a year: 108 hours of extra spindle time.

Anti-bacterial tank wash: when to schedule, when to skip

Posted on by Codeller

Anti-bacterial machine and tank wash is not something you do on the calendar. You do it when the coolant is telling you it is time. The rest is money you did not need to spend.

Signs the sump wants a wash

  • pH creeping below 8.6 and refusing to come back up with a top-up.
  • Rotten-egg smell first thing on a Monday, gone by mid-shift. That is anaerobic activity in the low-flow zones of the tank.
  • Dermatitis reports from the operators. That one is not optional. Book the wash.

Signs the sump is fine

  • Refractometer reading holding steady week to week.
  • Skimmed tramp oil coming off cleanly and consistently.
  • No visible biofilm on the return pipe when you dip a torch in.

What a proper wash includes

If it is scheduled, the job we quote covers: pump-out, mechanical clean of the tank walls, chase every dead-leg with the sanitiser, refill and re-inhibit, and a follow-up refractometer check at 48 hours to confirm the ratio held. Anything less is a rinse, not a wash.

The shortest-lived washes we see are the ones where the tank got cleaned but the machine bed did not, so the biofilm was seeded back in on the first cycle.