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Truncated Woodruff Key and gears

Somethings Gotta Give!

In the words of John Butler "Somethings Gotta Give right now"

The weakest part always has to give, and sometimes that weak part is a surprise to us all!

This week, one of our long time clients, a major international hotel chain called us to look at one of their Polivac polishers that had no torque.

As soon as the abrasive pad touched the floor, the pad stopped rotating. The motor kept going smoothly, with no noticeable increase in load, and it didn't trip the overload.

We brought the machine back to our workshop, and Roland first decided to change the RUN capacitor, but this made no difference.

The motor was warming slightly, and I thought it might be the motor windings breaking down.

The next thing Roland did, was turn the machine upside down, and remove the final drive from the gearbox. The gear drive was perfect with no sign of wear, and the gearbox oil was clear and clean.

The direct drive from the motor was faultless, so Roland had a close look at the parts list, and we could see the large brass gear had a Woodruff key, locating it to the final drive shaft. "Maybe the Woodruff key is the fault" he wondered. However, other than it being missing altogether, there isn't much to go wrong with a Woodruff key.

After removing the top bearing on the final drive, everything still looked perfect, no metal filings or signs of overheat with shades of blue on the metal. The softer bronze drive gear still looked brand new.

Roland then applied the puller to the bronze gear, which came away as you'd expect, however, it then revealed it's surprise, for the top part of the crescent shaped Woodruff key, had been sheared off, as neat as if it had been cut with a pair of scissors!

 Truncated Woodruff Key  Woodruff Key Almost Part Of Shaft

It took a while to extract the crescent part of the truncated Woodruff key from the shaft, and other than the U/S key, the rest of the drive was perfect.

Drilling Out Woodruff Key      Woodruff Key Freed

All that was needed was a replacement Woodruff key and reassemble the gearbox with some fresh gear oil, and we returned the polisher to its owner.

If Roland and I hadn't seen this with our own eyes, we might have been sceptical of something like this happening, with so little damage!

Andy Hawcroft

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