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
As always, common sense will keep you safe as much as anything else.
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
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.
Doug Miller (alphageek at milmac dot com)
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.
Your physics is certainly correct; gravity only has a split second to act on
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.
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
(PS Toller - if you're going to post trivial equations, at least get a
schoolkid to check them first)
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
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.
Doug Miller (alphageek at milmac dot com)
On Sun, 03 Dec 2006 18:06:47 GMT, email@example.com (Doug Miller)
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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