Just curious as what to expect if a 2" square x 24" piece of stock should come loose from lathe at 2000 rpm....... Would it just fall to the workbench..... Go flying across the room..... or lodge into my head? I would imagine that when you turn bowls things can kind of explode all over the place but not sure about a thinner piece when doing spindle work.
-thanx
Think back to your Physics class. It will go opposite the last force it encounters. Keep your toolrest between yourself and the piece, and cut slightly above centerline.
"buck" skrev i melding news:35669$41a201fb$44a7e404$ snipped-for-privacy@msgid.meganewsservers.com...
A good sized pece of wood at too high speed _has_ been known to kill people. From personal experience I saw such a piece of wood careen around my fathers shop, and kill his zest for woodturning. (Plus it gave him torn skin and hurt pride.)
Someone could (maybe) calculate the energy in the 2by24 you describe? I'm not that good with numbers.
Bjarte
Here in the UK it is "Sods Law" that the piece will fly off the lathe in the most dangerous trajectory possible.
Like buttered toast always landing face down on the floor.
In all the years that I have practiced turning dangerous pieces of timber, not once have they landed safely out of harms way. I am so happy that because of my slow reaction times I insist on wearing my full face visor otherwise my features would have been remodelled several times over.
Do not take the chance, expect the worst!
Regards, Peter Charles Fagg Freshwater, Isle of Wight, United Kingdom.
Hmmmm. Wasn't Murphy and Englishman?
Max
MURPHY!? Irish, surely.
Dave in Fairfax
================================== Peter, Here in the other side of the pond, that's known as "Murphy's Law". "O'Toole's Corollary" says Murphy is an optomist! {:-)
Ken Moon Webberville, TX
There is no predicting the direction. You may have observed that some turning respirator gear looks like a hard hat for good reason. I wouldn't consider turning without a full-face shield as a minimum. My biggest disaster was a piece held by one end in a chuck (it should have had the tailstock as well) that went up hit the ceiling, then a lamp on the way down before contacting the band of my face-shield. Fortunately I wasn't injured but it got my attention in a hurry. I think that a spindle is less likely to come loose and fly since if they loosen you notice it by poor or lack of drive.
Other woodworking tools can maim you, a lathe can kill you! Billh
I've had three bowl chunks and one spindle hit me square in the face. On all four occasions I was wearing my face shield. Three of the times the shield was actually down.
Now I ALWAYS wear a face shield....down.
Jack Savona
Well, an Englishman name of Newton disagrees. He says opposite the impact. That's why you keep your toolrest close to make sure it hits there before it enters a navel battle with you, and cut above center so a catch knocks it down. From that point on, everything it hits, according to Newton, takes half the hurt potential away in the impact.
More interesting is that doubling the speed equals four times the initial energy, which goes back to an answer I gave earlier about spindle turnings - slower is _much_ safer - so turn at a speed commensurate with your best edge, and don't be tempted to get more energy in the equation to compensate for a dulling edge or a poor presentation. Change the presentation or refresh the edge. Fortunately I don't have an instant speedup capability on my old iron beast, so it's actually easier to freshen the edge.
IME, 99% of the time spindles drop right on the bed of the lathe, shortly after hitting the toolrest. There are many other good reasons to keep the toolrest close in. I have had chunks fly by when a chunk split off the workpiece, but mostly it's been pretty boring.
A good high-impact face sheild is a good idea, regardless.
If it helps with your peace of mind, you can also get one of those wierd-looking cage guards for spindles. If spindles were all you did, it might not be too annoying.
As others have noted, keep the speed reasonable, which keeps the energy down.
George, Theory is great, but there is a rotational component to the piece, so if it comes loose and contacts something it will tend to climb up it. Where did Newton say anything about every hit takes half the hurt potential away? There are elastic and inelastic collisions, in an inelastic collision with one object moving and one anchored, there is a change in direction of the one object with minimal change is speed. As an example drop a golf ball on to a hard surface, it will bounce up more than half the height it was dropped from. Your suggestions for turning safely should be heeded none the less. Martin
I think it would be more useful to ask 'what would cause the piece to come off the lathe in the first place'. If you are having spindles come loose when turned between centers, seems to me like something is seriously wrong. I can't think of many scenarios:
- the spur point cuts a groove through the end of the wood if you have a catch. Most likely if the wood is soft or the spur point is not driven far enough into the wood.
- the wood breaks, possibly if the grain is not straight, has a knot or other defect, or if it is abused by the turner:)
- the tailstock and quill are not locked in place.
If in doubt, check everything before starting the lathe, stop at intervals during the job and check again. By all means wear a face shield just in case, but if you really feel that the wood is going to come off the lathe, tackle some smaller and simpler jobs until you have gained more experience and confidence.
Seatbelts and airbags are no substitute for good driving and proper training.
I've never been hit by one... had a few long pieces like that drop off and get dinged.. One bowl came off and rolled around the shop for a while.. lol seems like they went down and away from me before hitting something and bouncing..
Oversimplification, I'll admit. The initial "hit" which I'm going to presume will come from a tool, is the only one which doesn't necessarily worry about incidence/reflection, etc. That's why it should be forced down by cutting position.
And the theory I learned - non quantum - was that the energy of a collision divided equally on the hitter and hitee. How about that scientific for scientific terminology!
Elasticity? I'd rather do inductance calculations....
Hey, Thanks to everyone for your input. I now have a much better idea of what to do, what not to do, and what to expect if I should screw up. I knew I came to the right place.
On Tue, 23 Nov 2004 21:39:01 -0700, "buck" wrote: ok, I'll admit it... My initial instinct when anything "clunks" or doesn't sound right is to flinch away from the lathe and turn my back on it.. catching a flying cylinder on the butt is embarrassing, but catching it on your head or face can ruin your whole day..
My worst case of flying timbers: Mounted a 6 x 6 x 50" piece and forgot to turn my speed down. The piece I was turning before this was at 2200 RPM. When I hit the start button the blank started to spin and it tore loose at the head stock, I knew that I had screwed up as soon as I turned the lathe on, but it was to late. It took out an 8 foot fluoresent light that was about 9 feet above my head, the blank then hit my work bench that was about
4 feet away and smashed a 3/4 X 2" piece of Maple that was used as an edge band on my bench. It then landed on the concrete floor and bounced and danced for a while. I was un-injured in the mishap. I never stand in front of the lathe when starting it up. I now always always always check my speed before starting the lathe. You should have seen the look on a co-workers face, he was walking by my area when this happened, his eyes looked like two plates.LOL Jim
That's strictly true only if the "hitter" and the "hittee" are identical. In the case where the "hittee" is much more massive than the "hitter", if the collision is perfectly elastic the hitter rebounds with nearly all of its original energy.
Generally speaking a well-mounted lathe can be considered an immovable object for the purpose of making a first approximation of the energy of a rebounding object. Of course the collision is not generally perfectly elastic, how far it deviates depends on what you're turning and what it hits--a piece of balsa will generally deform a lot more than a piece of lignum vitae. Unfortunately, that also means that in general the heavier the wood, the more energy it's going to retain.
Just remember that catching it in a kidney is no fun either.
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