Afternoon all-
I thought I'd relay a story from my coworker about his son. This man
came within inches of losing his life thru a sequence of very logical
and extremely reasonable steps.
A 4" thick piece of mahogany was being machined for tenons. The piece
was part of a huge 20' door and, as an oversized, required special
cautions, including that the safeties be removed from the machine.
Since mahogany is carcinogenic, they took the trouble to increase the
airflow to prevent the workers from being exposed to the dust. The
guides that were normally in place were too small to accommodate the
large piece of wood.
Apparently the door stile would be cut in two parts- once would make
the horizontal parts of the tenon and then it would be hand sawn to
make the verticals. The piece was so large that it was bigger than
even what the CNC machine could handle.
The gentleman's son had already completed this task on several other
pieces. While removing the this piece, however, he clipped the edge of
the rubber shield that was protecting him from the carcinogenic dust.
The 14" cutter head was instantly wrapped in a thick blanket of rubber
and, under the force of a 20hp motor, shattered.
The sensation, as described, was little more than a small 'kick' to the
stomach and chest. For a moment he looked down and tried to understand
what exactly had happened- obviously the 20' piece of mahogany hadn't
kicked back otherwise he wouldn't have been standing. In seconds,
however, he began to 'spurt blood'- rapidly, too. Three pieces of the
carbide cutterhead had punched thru his stomach and chest. At the
speed of 7200 rpm they left at over 400 fps and the equivelent energy
of being shot with a .357.
Surgery was touch and go for several days- multiple surgeries were
required to repair all the damage and stop the bleeding. At least for
two of the days the doctors kept repeating they had no odds to provide
on whether or not he would live.
Even the most reasonable intentions and safety analysis can show
drastic flaws in hindsight. I quipped that another machine should be
bought. Another coworker pointed out that a simple kevlar vest would
have prevented the torso shots. You can imagine the suggestions and
ideas to prevent this disaster that were all offered up... in
hindsight. Machines are expensive. Bullet resistant vests are
expensive and (considered) by all to be overkill. A lexan face shield
scratches and is expensive to replace.
While I (obviously) don't have all of the details right (and I wasn't
going to push for much more) it just amazed me that this happeend in a
professional woodworking business that knew how to perform these tasks
safely (and has an outstanding record of this). The entire logical
arrangment was completely safe, up until they added the protection from
the carcinogenic dust generated by the mahogany wood.
Hope everyone stays safe and has a sane and productive year.
Jason
.357 projectiles are genreally approx. 1/3 oz. and travel at about
1200-1300 fps
CW wrote:
> The point of your story would have gotten across just fine without this
> serious exaggeration.
>
> <[email protected]> wrote in message
> news:[email protected]...
> > At the
>
>>speed of 7200 rpm they left at over 400 fps and the equivelent energy
>>of being shot with a .357.
>
>
>
>
>
CW wrote:
> The point of your story would have gotten across just fine without this
> serious exaggeration.
Just _which_ serious exaggeration? 14" cutterheads simply aren't spun
at 7200rpm. From that, the whole story starts to sound dubious. The
machine spindle might well run at this speed (it's high, but not
unheard of on modern kit) but it's not a safe speed to run on that size
of cutter.
Of course people working around big powerful machinery are at risk of
injury if things go wrong. Of course taking guards apart increases risk
(and it's rarely necessary - if the guard doesn't work, you need a
better guard, not no guard). The first rule of reporting such things
though is to be accurate and impartial. If you let hyperbole creep in,
then the chance of having a useful analysis of the accident and
avoiding it in the future diminishes.
For some years I designed and built machine control systems (big power
presses) and our office neighbours were a firm of forensic engineers.
Lots of interesting and useful conversations were had between the two
of us, on the topics of how to kill or maim workers and how to avoid
doing so.
[email protected] wrote:
> Afternoon all-
>
> I thought I'd relay a story from my coworker about his son. This man
> came within inches of losing his life thru a sequence of very logical
> and extremely reasonable steps.
>
> A 4" thick piece of mahogany was being machined for tenons. The piece
> was part of a huge 20' door and, as an oversized, required special
> cautions, including that the safeties be removed from the machine.
> Since mahogany is carcinogenic, they took the trouble to increase the
> airflow to prevent the workers from being exposed to the dust. The
> guides that were normally in place were too small to accommodate the
> large piece of wood.
>
> Apparently the door stile would be cut in two parts- once would make
> the horizontal parts of the tenon and then it would be hand sawn to
> make the verticals. The piece was so large that it was bigger than
> even what the CNC machine could handle.
>
> The gentleman's son had already completed this task on several other
> pieces. While removing the this piece, however, he clipped the edge of
> the rubber shield that was protecting him from the carcinogenic dust.
> The 14" cutter head was instantly wrapped in a thick blanket of rubber
> and, under the force of a 20hp motor, shattered.
>
> The sensation, as described, was little more than a small 'kick' to the
> stomach and chest. For a moment he looked down and tried to understand
> what exactly had happened- obviously the 20' piece of mahogany hadn't
> kicked back otherwise he wouldn't have been standing. In seconds,
> however, he began to 'spurt blood'- rapidly, too. Three pieces of the
> carbide cutterhead had punched thru his stomach and chest. At the
> speed of 7200 rpm they left at over 400 fps and the equivelent energy
> of being shot with a .357.
>
> Surgery was touch and go for several days- multiple surgeries were
> required to repair all the damage and stop the bleeding. At least for
> two of the days the doctors kept repeating they had no odds to provide
> on whether or not he would live.
>
> Even the most reasonable intentions and safety analysis can show
> drastic flaws in hindsight. I quipped that another machine should be
> bought. Another coworker pointed out that a simple kevlar vest would
> have prevented the torso shots. You can imagine the suggestions and
> ideas to prevent this disaster that were all offered up... in
> hindsight. Machines are expensive. Bullet resistant vests are
> expensive and (considered) by all to be overkill. A lexan face shield
> scratches and is expensive to replace.
>
> While I (obviously) don't have all of the details right (and I wasn't
> going to push for much more) it just amazed me that this happeend in a
> professional woodworking business that knew how to perform these tasks
> safely (and has an outstanding record of this). The entire logical
> arrangment was completely safe, up until they added the protection from
> the carcinogenic dust generated by the mahogany wood.
>
> Hope everyone stays safe and has a sane and productive year.
>
> Jason
Well, call me prehistoric, but why even use a machine at all if all
they're doing is cutting a tenon on a piece that large, especially if
they're not mass producing it.
Andy Dingley <[email protected]> wrote:
> CW wrote:
>
> > The point of your story would have gotten across just fine without this
> > serious exaggeration.
>
> Just _which_ serious exaggeration? 14" cutterheads simply aren't spun
> at 7200rpm. From that, the whole story starts to sound dubious. The
> machine spindle might well run at this speed (it's high, but not
> unheard of on modern kit) but it's not a safe speed to run on that size
> of cutter.
< snip>
Andy-
I'm just repeating what his fathe said. This was part of a large door
and one of multiples being made. I had to take the speed of the
cutterhead as fact; and a 14" tenon bit, while large, isn't unheard of.
The linear angular velocity of the bit is pretty close to 440 fps at
the outer edge of the cutter at that given speed. I can try quizzing
him some more but I don't know what I'll get, and I doubt I'll get the
shop (very prestigious one, at that) any information off the machine
they were using.
In short, no exaggeration on my part, just relaying what I knew. If
the facts as presented to me were exaggerated I did try to spot check
as much as I could before presenting it. No malicious intent here...
just shocked at how quickly something could go wrong.
I'll see what I can find out.
[email protected] wrote:
> I'm just repeating what his fathe said.
> In short, no exaggeration on my part, just relaying what I knew. If
> the facts as presented to me were exaggerated I did try to spot check
> as much as I could before presenting it. No malicious intent here...
> just shocked at how quickly something could go wrong.
>
> I'll see what I can find out.
Don't worry about it. I see the point of your story. Basically, good
intentions (the cancer shield) can have disasterous unintentional
results. Naturally, this being usenet, people focus on insignificant
details such as whether the fragments were as powerful as a bullet..
whatever. I have a life, so I don't worry about it. I know you weren't
trying to decieve anyone with your story. Although maybe I'm the only
one :)
On Fri, 05 Jan 2007 12:21:45 GMT, [email protected] (Doug Miller) wrote:
>In article <[email protected]>, Mark & Juanita <[email protected]> wrote:
>>
>>OK, based upon previous posting that .357 shoots 1/3 oz bullet @1300 fps,
>>total energy is 1/2 m v^2
>>
>>1/2 * 1/3 * 1/16 * 1/32 * 1300^2 = 550.13
>
>Maybe I'm a little slow yet this morning (only one cup of coffee so far), but
>where does the 1/32 come from? The rest I see:
>
>1/2 is from mv^2 / 2
>1/3 is projectile weight in ounces
>1/16 to convert projectile weight to pounds
>1300^2 obviously is velocity squared
>
>But what's the 1/32 ?
>>
>>Now, to get that same equivalent energy, the mass required to have been
>>ejected at 400 fps:
>>
>>m = 2 / v^2 * E
>>
>>m = 2 / 400^2 * 550.13 * 32 = 0.22 lb = 3.52 oz
>
>Similarly, where does the 32 come from here?
As Todd pointed out -- Formula is for mass, so the 1/32 is needed to
convert from lb-force to lb-mass
+--------------------------------------------------------------------------------+
If you're gonna be dumb, you better be tough
+--------------------------------------------------------------------------------+
Yep. Bought one of those Chevy Vega station wagons back in the 70's. It
had heavy, reinforced doors, advertised to protect against side collisions.
Damn near crushed my fingers in that bear trap of a door. When the aluminum
engine started burning oil at 40,000 miles and the GM dealership service
manager obnoxiously insisted that I wasn't changing oil (I was - mechanical
engineer) and caring for the car (I was), I drove it to the Toyota dealer
and never looked back.
David Merrill
<[email protected]> wrote in message
news:[email protected]...
> snip...
> The entire logical
> arrangment was completely safe, up until they added the protection from
> the carcinogenic dust generated by the mahogany wood.
>
"CW" <[email protected]> wrote in message
news:[email protected]...
> <[email protected]> wrote in message
> news:[email protected]...
> > At the
>> speed of 7200 rpm they left at over 400 fps and the equivelent energy
>> of being shot with a .357.
>
> The point of your story would have gotten across just fine without this
> serious exaggeration.
According to my sources, a .357 slug has a weight of about 125 gr. and a
speed of 1450 fps. For an equivalent amount of energy at 438 fps, there
would have to have been roughly 10 times the mass, which works out to about
80 grams combined.
todd
[email protected] wrote:
> Afternoon all-
>
> I thought I'd relay a story from my coworker about his son. This man
> came within inches of losing his life thru a sequence of very logical
> and extremely reasonable steps.
>
> A 4" thick piece of mahogany was being machined for tenons. The piece
> was part of a huge 20' door and, as an oversized, required special
> cautions, including that the safeties be removed from the machine.
> Since mahogany is carcinogenic, they took the trouble to increase the
> airflow to prevent the workers from being exposed to the dust. The
> guides that were normally in place were too small to accommodate the
> large piece of wood.
>
> Apparently the door stile would be cut in two parts- once would make
> the horizontal parts of the tenon and then it would be hand sawn to
> make the verticals. The piece was so large that it was bigger than
> even what the CNC machine could handle.
>
> The gentleman's son had already completed this task on several other
> pieces. While removing the this piece, however, he clipped the edge
> of the rubber shield that was protecting him from the carcinogenic
> dust. The 14" cutter head was instantly wrapped in a thick blanket of
> rubber and, under the force of a 20hp motor, shattered.
>
> The sensation, as described, was little more than a small 'kick' to
> the stomach and chest. For a moment he looked down and tried to
> understand what exactly had happened- obviously the 20' piece of
> mahogany hadn't kicked back otherwise he wouldn't have been standing.
> In seconds, however, he began to 'spurt blood'- rapidly, too. Three
> pieces of the carbide cutterhead had punched thru his stomach and
> chest. At the speed of 7200 rpm they left at over 400 fps and the
> equivelent energy of being shot with a .357.
>
> Surgery was touch and go for several days- multiple surgeries were
> required to repair all the damage and stop the bleeding. At least for
> two of the days the doctors kept repeating they had no odds to provide
> on whether or not he would live.
>
> Even the most reasonable intentions and safety analysis can show
> drastic flaws in hindsight. I quipped that another machine should be
> bought. Another coworker pointed out that a simple kevlar vest would
> have prevented the torso shots. You can imagine the suggestions and
> ideas to prevent this disaster that were all offered up... in
> hindsight. Machines are expensive. Bullet resistant vests are
> expensive and (considered) by all to be overkill. A lexan face shield
> scratches and is expensive to replace.
>
> While I (obviously) don't have all of the details right (and I wasn't
> going to push for much more) it just amazed me that this happeend in a
> professional woodworking business that knew how to perform these tasks
> safely (and has an outstanding record of this). The entire logical
> arrangment was completely safe, up until they added the protection
> from the carcinogenic dust generated by the mahogany wood.
>
> Hope everyone stays safe and has a sane and productive year.
>
> Jason
"Safeties be removed from the machine":
A modification for "carcinogenic" dust:
Each one the largest NO-NO of every business and hobbyist alike. I hope
they have good insurance because if they send out an investigator to look
that over ... .
I'm not unsympathetic, really, but ... those two opening salvos pretty much
set it up for a disaster which was not an "if" but a "when". Murphy never
sleeps! and "right tool for the job" prevails here. It was a worthwile
lesson, I hope; maybe not.
Glad he's still got his guts and chest at least!
Pop`
"Prometheus" <[email protected]> wrote in message
> Doesn't really matter if the projectile was going as fast as a bullet
> or an arrow, or a speeding car- if it pops one of your organs, that's
> reason enough to avoid the situation.
Well it certainly matters to the victim once healed and telling the story
over a couple of beers. "it was a 36" wheel that disintegrated and just
like a meteor . . . . . . . .
"CW" <[email protected]> wrote in message
news:[email protected]...
> The point of your story would have gotten across just fine without this
> serious exaggeration.
>
> <[email protected]> wrote in message
> news:[email protected]...
> > At the
>> speed of 7200 rpm they left at over 400 fps and the equivelent energy
>> of being shot with a .357.
We don't know the size and *weight* of the pieces that struck the victim.
The energy in pounds foot *could* have been equal to a .357 slug.
Max
On Fri, 05 Jan 2007 04:15:50 GMT, "Max" <[email protected]>
wrote:
>
>"CW" <[email protected]> wrote in message
>news:[email protected]...
>> The point of your story would have gotten across just fine without this
>> serious exaggeration.
>>
>> <[email protected]> wrote in message
>> news:[email protected]...
>> > At the
>>> speed of 7200 rpm they left at over 400 fps and the equivelent energy
>>> of being shot with a .357.
>
>We don't know the size and *weight* of the pieces that struck the victim.
>The energy in pounds foot *could* have been equal to a .357 slug.
>
>Max
>
>
OK, based upon previous posting that .357 shoots 1/3 oz bullet @1300 fps,
total energy is 1/2 m v^2
1/2 * 1/3 * 1/16 * 1/32 * 1300^2 = 550.13
Now, to get that same equivalent energy, the mass required to have been
ejected at 400 fps:
m = 2 / v^2 * E
m = 2 / 400^2 * 550.13 * 32 = 0.22 lb = 3.52 oz
For the size of cutter, that doesn't seem too implausible
Note: this assumes the 400 fps estimate is correct, it further asssumes
that the .357 projectile mass and velocity estimates are correct. Finally,
it assumes that I did my math correctly. I'm not sure that the 400 fps
estimate is correct, 14" cutter head @7200 rpm would be moving at 440 fps
(close enough)
+--------------------------------------------------------------------------------+
If you're gonna be dumb, you better be tough
+--------------------------------------------------------------------------------+
"Doug Miller" <[email protected]> wrote in message
news:[email protected]...
> In article <[email protected]>, Mark & Juanita
> <[email protected]> wrote:
>>
>>OK, based upon previous posting that .357 shoots 1/3 oz bullet @1300 fps,
>>total energy is 1/2 m v^2
>>
>>1/2 * 1/3 * 1/16 * 1/32 * 1300^2 = 550.13
>
> Maybe I'm a little slow yet this morning (only one cup of coffee so far),
> but
> where does the 1/32 come from? The rest I see:
>
> 1/2 is from mv^2 / 2
> 1/3 is projectile weight in ounces
> 1/16 to convert projectile weight to pounds
> 1300^2 obviously is velocity squared
>
> But what's the 1/32 ?
>>
>>Now, to get that same equivalent energy, the mass required to have been
>>ejected at 400 fps:
>>
>>m = 2 / v^2 * E
>>
>>m = 2 / 400^2 * 550.13 * 32 = 0.22 lb = 3.52 oz
>
> Similarly, where does the 32 come from here?
>
> --
> Regards,
> Doug Miller (alphageek at milmac dot com)
>
> It's time to throw all their damned tea in the harbor again.
Well, I don't drink coffee at all, but without putting a lot of thought into
it, could it be the conversion from lbs-force to lbs-mass?
todd
In article <[email protected]>, Mark & Juanita <[email protected]> wrote:
>
>OK, based upon previous posting that .357 shoots 1/3 oz bullet @1300 fps,
>total energy is 1/2 m v^2
>
>1/2 * 1/3 * 1/16 * 1/32 * 1300^2 = 550.13
Maybe I'm a little slow yet this morning (only one cup of coffee so far), but
where does the 1/32 come from? The rest I see:
1/2 is from mv^2 / 2
1/3 is projectile weight in ounces
1/16 to convert projectile weight to pounds
1300^2 obviously is velocity squared
But what's the 1/32 ?
>
>Now, to get that same equivalent energy, the mass required to have been
>ejected at 400 fps:
>
>m = 2 / v^2 * E
>
>m = 2 / 400^2 * 550.13 * 32 = 0.22 lb = 3.52 oz
Similarly, where does the 32 come from here?
--
Regards,
Doug Miller (alphageek at milmac dot com)
It's time to throw all their damned tea in the harbor again.
In article <[email protected]>, "todd" <[email protected]> wrote:
>"Doug Miller" <[email protected]> wrote in message
>news:[email protected]...
>> In article <[email protected]>, Mark & Juanita
>> <[email protected]> wrote:
>>>
>>>OK, based upon previous posting that .357 shoots 1/3 oz bullet @1300 fps,
>>>total energy is 1/2 m v^2
>>>
>>>1/2 * 1/3 * 1/16 * 1/32 * 1300^2 = 550.13
>>
>> Maybe I'm a little slow yet this morning (only one cup of coffee so far),
>> but
>> where does the 1/32 come from? The rest I see:
>>
>> 1/2 is from mv^2 / 2
>> 1/3 is projectile weight in ounces
>> 1/16 to convert projectile weight to pounds
>> 1300^2 obviously is velocity squared
>>
>> But what's the 1/32 ?
>>>
>>>Now, to get that same equivalent energy, the mass required to have been
>>>ejected at 400 fps:
>>>
>>>m = 2 / v^2 * E
>>>
>>>m = 2 / 400^2 * 550.13 * 32 = 0.22 lb = 3.52 oz
>>
>> Similarly, where does the 32 come from here?
>>
>Well, I don't drink coffee at all, but without putting a lot of thought into
>it, could it be the conversion from lbs-force to lbs-mass?
Yep, I think you nailed it. Thanks.
--
Regards,
Doug Miller (alphageek at milmac dot com)
It's time to throw all their damned tea in the harbor again.
On 5 Jan 2007 07:15:41 -0800, [email protected] wrote:
>I'm just repeating what his fathe said. This was part of a large door
>and one of multiples being made. I had to take the speed of the
>cutterhead as fact; and a 14" tenon bit, while large, isn't unheard of.
> The linear angular velocity of the bit is pretty close to 440 fps at
>the outer edge of the cutter at that given speed. I can try quizzing
>him some more but I don't know what I'll get, and I doubt I'll get the
>shop (very prestigious one, at that) any information off the machine
>they were using.
>
>In short, no exaggeration on my part, just relaying what I knew. If
>the facts as presented to me were exaggerated I did try to spot check
>as much as I could before presenting it. No malicious intent here...
>just shocked at how quickly something could go wrong.
>
>I'll see what I can find out.
Go ahead if you like, but I think the point is clear enough without
poking into what is likely to be a pretty touchy subject around that
shop. Let's just say it was a few hunks of sharp metal going fast
enough to impale a guy, and let those folks get on with getting past
what sounds like a pretty nasty day at work. I'm sure we'll survive
without diagrams and expert witnesses.
Doesn't really matter if the projectile was going as fast as a bullet
or an arrow, or a speeding car- if it pops one of your organs, that's
reason enough to avoid the situation.
Highly unlikely.
"Max" <[email protected]> wrote in message
news:[email protected]...
> We don't know the size and *weight* of the pieces that struck the victim.
> The energy in pounds foot *could* have been equal to a .357 slug.
>
> Max
>
>
>
.357 projectiles are generally approx. 1/3 oz. and travel at about
1200-1300 fps
CW wrote:
> The point of your story would have gotten across just fine without this
> serious exaggeration.
>
> <[email protected]> wrote in message
> news:[email protected]...
> > At the
>
>>speed of 7200 rpm they left at over 400 fps and the equivelent energy
>>of being shot with a .357.
>
>
>
>
>
The point of your story would have gotten across just fine without this
serious exaggeration.
<[email protected]> wrote in message
news:[email protected]...
> At the
> speed of 7200 rpm they left at over 400 fps and the equivelent energy
> of being shot with a .357.