Tuesday, May 09, 2006

Danger around every corner

I have been making weedpots today, a job I have done thousands of times before. The wood was roughed down and was held securely by a tenon in a chuck. I was at the stage of boring the hole, with the drill bit held in a Jacobs chuck in the tailstock. I decided to withdraw the drill bit to clear the flutes, and rather than wind the quill all the way back, I loosened the tailstock and slid that back.

I don't know how far I had got because it all happened rather fast:) The Jacobs chuck came out of the morse taper and flew through the air. Fortunately it went away from me and hit the wall. It missed the window too, so the only damage was a dent in the Gyproc. If someone had been watching from the other side of the lathe, or the drill had come towards me, the outcome may have been considerably more serious.

So what went wrong and what can be learnt from this experience? I had already made several weedpots with this set-up, so the morse taper on the Jacobs chuck must have been rammed home securely. I had also used the same technique of sliding the whole tailstock back to remove the drill bit from the wood.

Obviously the friction between wood and drill bit was sufficient to loosen the morse taper, but why? It could be because this blank was partially spalted, so it is possible the drill had wandered a little off-center towards the softer material. This might cause it to bind. Also as the flutes filled up the friction undoubtedly increased. Either way the rotating wood grabbed the bit and was able to pull and twist the morse taper out.

The lessons to learn? Withdrawing the bit by sliding the tailstock is inherently dangerous, especially if slid back too quickly to notice the drill chuck coming loose. If I do this again, I will do so with less haste and will be sure to have one hand on the tailstock and one on the Jacobs chuck.

Turn safely. Be aware of the dangers.

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