How dangerous are lathes?

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Not true at all. There's a hunk of wood spinning around, and you're jabbing a sharp piece of metal into it. Provided you're careful, it's safe enough, but it's just as dangerous as any other tool, and more dangerous than some.

Depends on what you're doing- I've had it happen a few times when cutting wet wood very thin. It dries on the lathe, and if it cracks, it will explode off at fairly high velocity. More *dangerous* to my mind are spinning chuck jaws that can quickly tear all the skin off a knuckle or remove a fingernail if you get too close, and getting something loose wound around the spindle. Easy to bust up a finger or two if you're sanding the inside of a hollow form like a vase with sandpaper held in your hand.

It's strong enough- unless you're doing something really crazy, like turning wood with live ammunition in it. Think about it for a minute- the rotational force of the piece isn't the only thing that affects how it's going to fly off if something breaks or is not held correctly. Gravity has it's say as well- and from previous exerience when I got my first chuck, anything that could possibly be heavy enough to break the sheild drops just as fast or faster than it is moving towards you. Most heavy things will fall fast, then roll along the floor- not shoot at you like a cannonball. The face shield will easily save you from high velocity splinters and smaller chunks of wood that are moving really fast, and those are the dangers that piece of equipment is guarding you against.

A dust mask is always a good idea, not matter what you're doing to make dust.
As always, common sense will keep you safe as much as anything else.
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The laws of physics dictate quite the opposite, in fact. To begin with, the mass of an object has absolutely nothing to do with how fast it falls (as was famously demonstrated by Galileo some five centuries ago).

Again -- the velocity of a falling object is completely independent of its mass.
Which direction it goes depends mostly on which direction it's moving when it comes loose (e.g. on the back side of the work, moving upward -- it's gonna launch!); at even modest rotational speeds, the velocity of the circumference of a large workpiece exceeds anything that would be imparted by gravity in the very short distance between spindle or faceplate and the shop floor.
Example: 10-in diameter workpiece rotating at 500 rpm; lathe center at 42" above the floor.
The edge of the workpiece is moving at (10 pi * 500) inches per minute almost 22 feet per second -- but an object falling only 42" doesn't attain a velocity of quite 15 fps before it hits the floor.
--
Regards,
Doug Miller (alphageek at milmac dot com)
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wrote:

Think he's talking about the standard 1/2 MV sq inelastic collision accomplishing some heavy deceleration. Since we're pretty much confined to earth with our turnings, the M is going to be equal to weight, and it's part of that equation.
Rather not have a shield. Cuts down on the number of random directions a piece might take on the ricochet. Just stand out of the zone and let 'er fly if she cares, though with a modicum of effort no reason it should.
Most machine injuries I've seen contained some element of pursuit of the piece rather than letting it fly where it would predictably go and the injured should not be. Buck twenty nine worth of walnut becomes a 1500 dollar ambulance ride and that's only the beginning.
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wrote:

the object, so imparts very little velocity on it. (mv=ft and all that...) Yet intuitively it seems that things should tend to fall down rather than up. Yes, I know intuition is wrong half the time, but still...
It has been a very very long time since I did any of this. f from the rotation is proportionate to the m of the object in question, so the mass doesn't matter there either.
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Doug Miller wrote:

Not at all - the velocity of _freely_ falling objects is independent of mass, but lathe turnings aren't usually freely falling -- they're spinning objects in passing contact with some fixed point that can impart a force to them. If they're balanced and they fall free from the chuck then it's no problem - if they catch on the way down, it can get hairy.
(PS Toller - if you're going to post trivial equations, at least get a schoolkid to check them first)
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What do you mean, "not at all"? That was demonstrated by Galileo about five hundred years ago.

They are the moment they come loose from the lathe, which is the issue at hand. As long as they stay attached, they are not falling objects, and therefore not relevant to the discussion.

Yes, and that's one of the points I was making -- the force imparted to them by the lathe is, in most circumstances, of greater magnitude than that imparted by gravity.

If balanced, sure -- but what if something *breaks*? Then, it's no longer balanced -- and the direction that broken-off piece moves depends on the direction it was moving when it came free, and has *nothing* to do with its mass.
Also note that a perfectly balanced lightweight piece that simply comes loose will drop straight down, too, just like a perfectly balanced heavy one that simply comes loose.
The behavior of falling objects in a gravity field is completely independent of their mass (except to the extent that objects with very low *density* will fall more slowly due to aerodynamic effects). In vacuum, a feather and a stone fall at the same rate -- and even in air, there is no difference discenible without the use of laboratory equipment between the velocity of falling stones of, say, 1 kg and 10 kg, when dropped from the same height.
Whether a chunk of wood that comes loose from a lathe goes up, down, or sideways has NOTHING to do with its mass.
--
Regards,
Doug Miller (alphageek at milmac dot com)
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Yep. I've got a bruise on the noggin that says you're right. Previous experiences with the chuck letting go were mostly right after mounting, and didn't involve a cutting tool.
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On Sun, 03 Dec 2006 18:06:47 GMT, snipped-for-privacy@milmac.com (Doug Miller) wrote:

I'll grant you this one, as I managed to whack myself square in the forehead with a blank earlier this evening. Didn't fly straight off, though- it rolled up the tool, up my arm, and then popped up when I reflexively yanked back and straightened my arm. Didn't feel nice... but it was an eloquent rebuttal to what I wrote above!
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