How do you prevent a turned workpiece from exploding while you're working on it on the lathe?

Question

I've seen some scary videos and "after" photos where someone was turning something on a lathe and the workpiece just exploded. How do I avoid this?

For example, in one exploding bowl video the turner comments that he made the bottom too thin which makes sense but he doesn't go into any detail about how thick it should have been. Is there a quick-and-dirty rule for estimating how thick the bottom and/or sides should be? He also mentions the wood was a little wet but I'm not sure if he's suggesting that was also part of the cause.

Is it common for things to explode on the lathe, and is it more due to operator error or just an understood hazard of turning wood? If I can't do anything to completely prevent it, what rules of thumb can I follow to at least decrease the chances of my workpiece exploding on the lathe?

Also, is there a technical term for this (similar to the term "kickback" in relation to other tools), or is it just called exploding?

Answer 1

The video (and details from the comments and video itself) make a great case study. Wet wood can be inherently unstable as it may have uneven mass distribution, integral stresses that are unbalanced and a myriad of other factors.

Think about how when a piece of wood bows/warps/twists as it dries. That is the wood exhibiting and forming to its inherent stresses. Now, go exploring that stress while spinning it VERY fast, AND causing some rather large centripetal forces AND removing its material, further changing how the stress, mass and forces are distributed.

This happens from time to time. I would say burls, greenwood, and similar pieces have a higher likelihood of this, however I would still not call it common. I have had less than 10 pieces 'FRAG'on me out of hundreds.

When in doubt, or while learning err on the side of caution. Take your time, start slow (and speed up as necessary) and be cautious if anything feels wet, hot, unstable, or seem's 'tensed' up.

Good luck. May your blades stay sharp and your wood chips plentiful.

Answer 2

As BrownRedHawk says, it's not very common. The reason he didn't say how thick it should have been is because 'it depends' mostly on the size of the bowl to begin with. Wet/green wood is also heavier and weaker than dried wood.

A clean piece of wood will generally not 'explode'. If there are cracks or branches or other 'issues' with the wood, it is much more likely. I had one split in half because there was natural crack that went a lot deeper than I thought and when I caught my chisel half of it just flew off. but I've had 2 pieces break on me like that and I'm in the low 100's for items turned.

It does enforce the idea to be careful though, turning looks safe, but only if you do it correctly.