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Evan
09-25-2003, 04:48 PM
Warning! Graphic description of lathe accident by victim himself. I think I'll be real carefull. This reminds me of those movies they used to show us in high school.

http://www.bookhaunts.com/Stories/Ouch.htm

3jaw
09-25-2003, 05:17 PM
I fink I'm gonna fwow up! http://bbs.homeshopmachinist.net//eek.gif

G.A. Ewen
09-25-2003, 05:54 PM
Couldn't read past the second paragraph, brings back bad memories from my youth.

Alistair Hosie
09-25-2003, 06:09 PM
It just shows you how not to be complacent around machinery.Shed machinist are you paying attention? I remember a few years ago a guy here was moving his lathe and it fell on him killed him outright Alistair

Techtchr
09-25-2003, 07:23 PM
I try to avoid the horror stories like this when teaching students to use machine. I want them to be careful and respectful but not scared to death of them.

So here goes my story; I worked with a lady who had a son that worked in a mobile home factory. They used a large sheet metal compactor to compress the scraps of metal siding to package them before recycling them. The machine jambed, so he made the mistake of reaching in to dislodge the jambed material. All guards had been removed from the machine. The machine broke free and caught his hand. Stretched his arm 6" longer than normal before he broke loose. The Doctors said that because he was a gymnast in HS just a few years before, his upper body strength kept the machine fom pulling his arm completely off. They said it would have been better off being severed because it is harder to repair the stretched tissue than cut tissue.

The management at the place scrambled to put the guards back on the machines. Last I knew, he was OK, but had very limited use of his arm.

So far, Knock on wood, neither I or my students have experienced more than a minor accident.

Be careful out there.

Matt

wierdscience
09-25-2003, 08:56 PM
I got a shirt tail wrapped up in a leadscrew once,that sucker spun me up to my throat before I got it stopped,luckily the lathe had the feed reverse on the carrage,otherwise I would have been there awhile myself.

I did get caught one other time,but I always wear thin clothing anyway and I just went the other way and ran out of my shirt.

I will not wear a coat or long sleave shirt,no way in hell,if its to cold,I either get a heater or go home for the day.

jim k
09-25-2003, 09:24 PM
Abuot a year before I started in the shop that I am in now a guy had his arm tore off.He was working alone on nite shift.Was running a 5" G&L hoizonal mill.Was holding a mirror and reaching in a bore as he was backfaceing a large part.Got wrapped up in the spindle somehow and it twisted it off.He sat down and removed his shoe and somehow took his sock off and tied off his arm above the elbow.Cant remember if neighbor called police.I do recall that they heard alot of screaming. He was working as a foreman when I started.Finally got total disability and quit.Nice guy he was.Cant believe he kept his senses in a situation like that.

Thrud
09-26-2003, 12:38 AM
The moral of this story is long shirt sleeves are a strict NO-NO> It is his own fault.

Most serious accidents are because of operator stupidity. If you are not going to pay attention you are going to get hurt.

I worked for a lot of years around heavy gauge sheet metal equipment (shears, Punch presses, Mechanical & hydraulic brakes. One of the best advances in safety in that field was hydraulic punch presses and brakes (shears rarely cut fingers or limbs off) - even so, there is considerable danger in working small parts in a hydraulic press brake. You need to pay close attention to what you are doing ALL OF THE TIME.

I had set a machine up for making SS clips - it was a 4'-50T Promechan (the die bed raises up for the stroke). I had the machine set so that if the operator made a mistake the worst thing that would happen was a blood blister. While I when back to my own work (his machine was behind my 12'-250T Accurpress) the operator decided he knew better and changed the set up. He got into a rithym and when he screwed one up instead of just mashing the part and throwing the "remains" away in the scrap, he reached into the die area and got his thumb caught in the dies. His thumb was compressed to 22Ga. thickness at which point it blew off. He come running around my machine, blood spraying all over. The bone in the stump splayed open like a little daisy (neat!). I got someone to call 911 and packed the wound, The other workers started a thumb pieces hunt - pieces were found thirty feet away.

This guy was lucky I knew what to do - the microsurgeon was able to reconstruct his thumb - I could not tell (if I did not know what had happened) which thumb was blown off. He bitched about weather driving him nuts, I told him at least he could still use his thumb...(true story)

abn
09-26-2003, 03:19 AM
Damn, I've got to get me one of those big red emergency off switches and start bringing the phone out to my container...I'm always working alone and usually at night.

SJorgensen
09-26-2003, 03:40 AM
I think these are great stories. It is useful and I just wish we could all be telling them around a campfire but we don't have that luxury tonight. My favorite Great Uncle was known for his horses. I took care of 36 of them for a few years. He had a thumb on on hand that was a little "floppy." I'll not give you the full story but a horse bolted and the rein was wrapped around his thumb and popped it off. He emphasised to me the importance of holding ropes in a proper way. If a horse bolts and you are holding a coil in your hand, you could be chasing your hand AND your horse.

Great lessons that we shouldn't have to learn first hand.

Spence

darryl
09-26-2003, 04:46 AM
I've been thinking of late about putting an 'off' bar on the table saw, so any portion of the bar I put my knee into, or kick, or whatever, it will shut off. After reading these stories, I'm going to consider how I can put something on the lathe and mill as well, to get a fast and/or hands free shutoff.

BC21OSH
09-26-2003, 05:59 AM
Evan,

That's a pretty graphic horror story, makes a person think when he walks up to the lathe.

The worst shop accident I witnessed was a similar type of situation, however not nearly that severe.

Two of us were working in the shop. The other guy was on a 13" South Bend Lathe and was trueing up a small Honda motorcycle sprocket in a center rest. He reached over the lathe with his left hand to adjust the center rest on the backside and the cuff of the industrial coveralls he was wearing caught on the rotating sprocket. It pulled his hand into the sprocket and acted like a dull cicular saw cutting into his palm.

The switch was behind the headstock and the coveralls wouldn't rip when he attempted to pull away. He was finally able to twist around enough to reach the switch with his right hand and shut the machine off but not before the sprocket had cut in pretty deep.

I saw him head for the sink holding his hand and not looking too well. I drove him to the ER.

A foot switch or knee switch would have been a plus in this case.

In that shop we had one lathe with a foot switch ( bar ) that also was a brake, it was great.

The other accident that I heard about but didn't witness happened at a factory next door to where I worked. A guy with a pony tail was operating a large drill press and leaned toward the rotating spindle to check the work. The spindle caught his hair and ripped his scalp off his head.

Bernard

Rustybolt
09-26-2003, 08:42 AM
Safety is the first thing that gets taught around any power tool.That hunk of metal is just a dumb machine, Its gonna keep going whether its cutting steel or a piece of your body. Its easier to keep what you already have than to try and sew it back on. Old words of wisdom from my father,bless his soul.
Are you listening shed?
I got all my parts because basically I'm a big chicken and don't like to see my own blood, so I make sure things are battened down and secured.

Now watch, after having said all this I'll do something stupid and cut off my thumb or something.

jr45acp
09-26-2003, 09:19 AM
I'm with Thrud, no long sleeves ever for any reason. My shop is in my unheated garage. It doesn't get cold here per se, but does get chilly with high humidity. In those times, I wear a tight fitting long underwear top with the sleeves pulled up to above the elbows. If still cold I layer up, but never with sleeves below the elbow.

On the other hand, I did have an electrifying event. I was welding the legs on a metal bench I was fabricating. Top was on the concrete, had one foot on the metal and one foot one the floor. Struck the arc and immediately started break dancing. Seems the light rain shower had splashed some water onto the floor where my foot was. Odd, as I had on neoprene sole boots. Be that as it may, I always check now for any wet spots. http://bbs.homeshopmachinist.net//redface.gif

------------------
John B

Michael Az
09-26-2003, 10:15 AM
I always work in the shop alone and live alone. Got in the habit of making sure I have my portable phone with me. I have fell down several times and you never know when you could break a hip. SJorgensen's horse story reminded me I once had a barber that had lost a hand in the rope when he was roping calf's.
Michael

MikeH
09-26-2003, 02:53 PM
I have seen several minor accidents and one major one. All of them reminds me to think before I act, and not to drink before working. The major one reminds to me to always wear my seat belt. A co-worker was loading a farm tractor onto a trailer. He made two mistakes, he was attempting to climb the step in the trailer without a ramp and was not wearing a seatbelt. The tractor slid of the side of the trailer, rolled over, and the roll bar landed on his elbow. He lost his arm. Most of the minor ones were due to the injured drinking before work. God, I am glad I got out of that place!

Mike

Thrud
09-26-2003, 05:10 PM
darryl:
They make a large 10"x 10" emergncy shut off switch for table saws it only needs a slight pressure to kill the saw. Fine Wordworking used to have advertisers selling them.

Rusty

All machines scare me enough that I too have great respect for them. (Cluck, cluck!) http://bbs.homeshopmachinist.net//biggrin.gif

[This message has been edited by Thrud (edited 09-26-2003).]

Paul Gauthier
09-26-2003, 07:23 PM
Do any of you know what a "Carding machine" is??? It is used in the textile industry, basicly it is two large rollers with spikes sticking out of them and wool is pulled between the rollers to get "carded", I don't know what that means I have never seen one myself, only the results of getting ones arm caught between the rollers.
One night when my youngest daughter was about 1.5 years old, (she is 35 now), she woke my wife and I by crying, she had a fever of 103, called doctor he said take her to emergency room at hospital and he would meet us there. So we got there and they put us in a exam room, said doc would be right in. While waiting I went out to the lobby to get a drink of water and heard a sceech of brakes and seconds later a man walked through the doors with just a stump of bone poking out from his left shoulder and bleeding profously. Needless to say all action was emidiatly centered upon this fellow. As I stood there stupified another guy came stumbling through the doors vertually unable to stand but unhurt. So I helped him over to a chair and he told me what happened. The injured fellow was operating a carding machine and got his hand caught in the rollers and could not reach the shutoff switch. As he was being pulled into the machine he had no choice but to pull back and literaly tore off his arm. He was into the machine up beyond his elbow when he finaly got free. It probably took less that ten seconds to happen. The other fellow heard him scream and found him standing there without his arm, took him out to his car and to the hospital which was less than 1/2 mile from the factory. The injured man insisted that they use his car so he would not get blood all over his friends car. Very sad, he was married with several kids.
I have seen some nasty things, accidents both motorcycle and auto (been into a few of my own) and industrial, but this was the first, and hopefuly last, missing limb. I had nightmares for weeks afterward.
I have been in this industry for about 35 years now and have run some very large machinery. Some of the forging dies I have made have wieghed up to 100 tons each half. I work for a forging company. So the machines must be correspondingly large. And if one is careless they can be very dangerous. So far I have not been seriously hurt. At the most I have had about 5 stitches on a finger. I credit my luck with having seen this fellow with the missing arm.
I no longer run the big machines, I now work on two Gidding & Lewis 4 Axis 48 inch cnc vtl's. Much safer, and less stressful.

------------------
Paul G.

rockrat
09-27-2003, 09:45 AM
Most of the shops that I have been working in or visiting have a string / rope running across the top of lathes about eyeball height. It is hooked to a limit switch that will kill the lathe in an emergency. The odd thing is that I have only seen this on process lathes and rolling mills and not on general machining lathes. I wonder if this is something I need to put on the equipment at home. Might not be a bad idea.
BTW, I didnt get but 1/2 way through the article. Yikes. http://bbs.homeshopmachinist.net//eek.gif

Digger
09-27-2003, 05:25 PM
Good story and it makes sense to be aware but have you noticed that other than a name mentioned there is no way to check up on this. Sounds like an urban legend starting.
If he got wound halfway round to start with and it kept pulling in in bit by bit over the time scale he say he must have had 10 foot long arms to start with.
Sorry but this don't ring true to me.

We have a small amount of woodworking machinery at the local depot here in Great Britain, just for crating parts up for the gulf. Talking to one of the service techs the other week and he said that under European law by December this year ALL, no exception, woodworking machinery must be able to stop in under ten seconds after hitting the E-Stop.
We are Ok as our table saw and band saw are newish but the tech says they are rushing around fitting brake modules onto all sorts of older machines.

Digger.

Oso
09-27-2003, 07:48 PM
Yeah, that ocurred to me, too many details. Never know though, people do surprising things under stress. And the story may be "as remembered", rather than "as happened".

Or it could be made up. Kinda like the story of the 4 foot lathe chuck unscrewing with the forklift and chains attached to it.
Too bad big chucks are bolted on, eh.....?

docsteve66
09-27-2003, 07:51 PM
I'm with Digger on this one. I only got half way through (according to scroll bar) but the details did not add up to me. I called it quits.

Thrud
09-27-2003, 08:26 PM
Digger:
A gentleman in the US developed a table saw that will stop instantly if it senses flesh touching the blade - at worst you get a very minor cut.

He has demonstrated this device at woodworking shows with weiners (oh, the humanity! http://bbs.homeshopmachinist.net//eek.gif ) - no, not the kind in yer pants ya dirty minded buggers!!! http://bbs.homeshopmachinist.net//biggrin.gif When weiners are fed into the running saw the weiner gets a nick and the blade stops instantly.

Apparently, the hundred dollars it costs to add it to machines is considered "too much" by the major saw makers (so much for concern for their customers safety - deplorable) and the fellow has been forced to try and market a saw himself. I hope he succeeds - it is quite an astounding invention. Unfortunately, it is not something that can be retrofitted. He should have tried marketing it to Euro saw makers - safety being a big issue over there and all.

[This message has been edited by Thrud (edited 09-27-2003).]

Evan
09-27-2003, 10:27 PM
I find it entirely likely that it is not of whole cloth. Still, I think I will rig a stop cord for my lathe, possibly even a stop for all power to the tools in my shop. When I built my electronics shop I put in a master switch that turns on/off all the outlets in the room. That way I don't have to worry if I left the soldering iron on or the variable power supply still connected and hot to a test circuit that might smoke later.

Oso
09-27-2003, 11:28 PM
Evan....Dude.....

You are my kind of think-ahead guy. Both my shops are like that. When I leave, master switch goes OFF. No questions afterwards.

And, I have lights with no switch, so you have to turn them off with the master.

My Father-in-law has his whole garage shop that way.

No other way to go, in my book.

Thrud
09-27-2003, 11:36 PM
Oso, Evan

All of the schools I went to here had 1 big, fat emergency button to kill the entire shop in emergencies. It is a smart idea for the home shop - if a mishap occurs a family member does not need to know how to operate the machinery to save your life.

A cordless phone is also a good idea - I have Siemens 2.4 Ghz cordless phones that fit nicely in a shirt pocket - they have intercom capability as well.

jfsmith
09-28-2003, 12:58 AM
I think people should pictures of some of these injuries, the words are fine, but one picture does a whole lot more.

We got any of them Paris Island Marines out there, did your DI should you the pictures the guys who tried to make it thru the swamp? Those pictures made you not want to every end up that way. You gained a lot of fear and respect for the swamp, didn't you?

Have that same fear and respect for machinery and you will do fine.

Jerry

Evan
09-28-2003, 01:37 AM
US Army, volunteer, Artillery, Headquarters Battery, fifth batallion, Second Brigade, Sixth Army West. Had a DI in basic that set off a squib about two feet from my ear during night combat exercise. "Williams, LISTEN UP!!" "Huh??" "You say somethin Drill Sargent?" He didn't razz me too bad. I felt real sorry for the National Guard guys. The were in their own platoon. Got stepped on real bad.

abn
09-28-2003, 07:40 AM
In another thread (I thought it was here bu t can't remember who to credit) it was mentioned to put some lights on another circuit from your shop's master cutoff switch so you don't get caught in the dark with machinery that may not have come to a rest yet etc. etc.

[QUOTE]Originally posted by Thrud:
Snip>All of the schools I went to here had 1 big, fat emergency button to kill the entire shop in emergencies.<End Snip

T Wise
09-28-2003, 08:36 AM
Urban legend maybe, there was a story a while back about a climber in the US, I think, who got his arm crushed by a falling rock, he was pinned for several days intil he took out his knife and cut off the arm, then walked five miles or so to a road where he found help.

I was in the hospital a few years back getting an infection tended to when they rolled in an older gentleman who was threading in a lathe when his sweater cought, his arm was broken in three or four places,with the bones sticking out, he was lucky enough to have someone shut off the machine and get him out. What stuck out in my mind was that he wouldn't let them cut off his jacket when it came time for the
x-rays. He was a tough old bugger, but taking off the jacket did make him growl a bit.

Another incident that I did witness was one I don't want to see again, We used to have a six foot air press brake, operated by an air baffel raising up the bottom die. this guy reached through the dies and then his one foot stepped on the foot switch. He couldn't step off the switch until it reached the end of the stroke as it was lifting him up onto his toes. lucky for him we were doing some air bends and there was room for his fingers at the bottom of the stroke,but they aren't designed to bend that way. some nasty cuts and stuff, but he was back to work in a couple of days. Bandaged up and sore, but eventually got full range of motion again.

Tim

Oso
09-28-2003, 09:52 AM
For that kind of machine, for years there has been safety stuff that is intended to prevent just that, at least during production.

double-buttons that you can't reach with both hands if one is in the machine. Been around for 60 years as an idea

NO foot buttons allowed, for the reason you mention.

more recently, light curtains that can sense an hand or head sticking thru and won't allow the cycle to start.

Yeah, they cut production rates....about 2%.....so what? Take it out of the salesman's commission..... http://bbs.homeshopmachinist.net//biggrin.gif

T Wise
09-28-2003, 11:22 AM
I forgot to ask, wouldn't instantly stopping a saw motor cause the blade to spin itself off the arbor??

Evan
09-28-2003, 01:52 PM
Apparently not. My chop saw has a brake that stops it in about one second. Saw blade is still attached. Now, for my OLD 10" radial arm saw, that is a different matter. I should hook up a diode to brake that sucker, it takes about 20 seconds to spin down. (PITA, requires digging into the switch and figuring out some way... Hmmm... Use switch to control a relay in a box. Yep. Can do.)

Thrud
09-28-2003, 03:17 PM
abn:
I should have stated that all outlets and machinery are killed - not the lights. The large machinery where all hard wired with no way to "unplug them" hence it was a requirement that there be a master kill switch. All the machines had power lockouts as well - that is, if power was restored they remained "turned off" until manually restarted machine by machine. All machinery should be wired this way if at all possible - it is an excellent safety feature.

This is actually what I meant - sorry for the confusion.

T-Wise

Personally, I could care less if the blade spins off (they don't anyway) - it is far more important to reduce injuries. If it a choice between the tool and me, the tool loses everytime. Tools can be replaced easily.

[This message has been edited by Thrud (edited 09-28-2003).]

tstalcup
09-28-2003, 03:21 PM
There's been a big discussion of the Saw Stop on some of the woodworking boards - it doesn't stop the motor directly, it cuts the power and drops the blade into a block of plastic.

I think no one is saying its a "bad" idea per se, but a lot of people are up in arms about the fact that the company is trying to pass a law requiring it on all new saws sold.

Thrud
09-28-2003, 03:33 PM
tstalcup:
I have several friends with missing fingers (all woodworkers) - they should have had this device weither they "wanted" it or not.

Radial saws are far more dangerous than a table saw, yet most fingers are lost on table saws.

Evan
09-28-2003, 03:48 PM
I still have all my fingers. I have never been bit by a saw. I am scared sh**less by fast moving sharp teeth. I am perfectly willing to wait until it is completely stopped to clear that cutoff piece near the blade. No problem. I don't like exposed blood.

docsteve66
09-28-2003, 07:50 PM
I think every injury I have has been while I was doing something "safe" when dead tired. Once, hand in joiner- about forty stitches, fat globules sticking out of the palm. ANother time, Picked up a heat gun by wrong end. Flesh charred. Both times dead tired.

Foot Switch, I rigged a air operated foot switch on a saw. Lift the foot and saw off. It was in series with the power switch and not intended as a safety device. But I guess it was- unless you walked away with power switch on- then it was a booby trap.

Safety man once caught "Reverend Rogers" (Preacher who worked in tool crib) marking tools in a laser tool marker. The Rev could snatch a tool, insert a tool while door was cycling. Safety brought the case to me- said the Rev should never insert hand into the cavity until the door was up and stopped. Safety asked for five day suspension. Rev did not want to spend five days with no pay so he argued- REv says the interlock goes off when the door starts moving to keep the laser beam from reflecting, so it is safe. Safety says, not safe till it get to top- I Want five days suspension. Rev says (paraphrased) "you are a racist- think us niggers (his words) don't knowhow to operate equipment - I am headed for EEO man". Safety asks if I support the Rev. I say that i am no fool nor is rev. I will give him five days off without depending on your note to me. Write it out. we are safety conscious men. Rev says he will take five with pay- safety says he won't write anything. Rev begs for letter of reprimand and five days with pay. Safety comes back-to Rev and says "what if interlock sticks then you are in danger". Rev says then I am in danger even if I don't do anything. Safety leaves, Rev puts in a "beneficial suggestion" suggesting modification. I gave him 700 dollars based on what safety claimed the possible losses were if rev did not "get religion" in the operation.

Best safety device is a thinking man who is aware of his dangers and has authority to make changes or refuse work. Machinery can help but a smart man can still get into trouble if he is unaware of the dangers.

This is a subject that shall never reach a real good conclusion.

darryl
09-28-2003, 09:59 PM
I always have a plan of attack when operating the table saw. If the piece jams, I don't ever let go of it, I hit the switch. I am designing a better kill switch for it. If there's a possibility of making a projectile out of some wood or other material, I'm out of the way of it. I have 'shot' pieces of wood into the cement wall behind the saw, not on purpose, but knowing it was likely, given the conditions. Sure enough, there it was, sticking out of the wall like an arrow. In short, I have learned to minimize the danger to myself, without becoming afraid of the machine. My dad told me a story of a fellow who got a 2x4 stuck into his belly while using a tablesaw. I think of that everytime I use it. The most dangerous situation for me is when someone 'helps' me.

Evan
09-29-2003, 01:13 AM
Actually, I lie. I think I have posted this before. I was bit by a saw, a chain saw, when I was young. The spike guard rattled off and I put the saw across my leg between bucking up some logs. I never felt a thing. We took a break and I looked at my left leg and saw a big tear in my jeans. I looked closer, wish I hadn't. That gash got infected by bush bacteria. A week later the doctor lanced it. That hurt worse than my broken arm, my dog bite, and anything else that I recall.

Al Messer
09-29-2003, 01:24 AM
I've had my Makita Bench Saw for years and I'm still scared of it. I have a pile of Pine 1 x's on the workbench right now that is supposed to be turned into pantry cabinet door frames for SWMBO as soon as I can get up the nerve. Funny thing though, Lathes, Shapers, Drills, and Milling Machines don't scare me nearly as much as that "speeding, whining, circular blade of steel."

SJorgensen
09-29-2003, 01:41 AM
Evan,
Theres even one more reason to hate Bush.
I didn't know he had is own bacteria, but that is what leaders of nations do I guess.

Table saws have my full respect and I think my shop teacher gave me all the information I needed. Kick backs are a serious issue and the cheesy anti-kickback devices are just in the way and more of a problem than a solution. I think the key is in knowing the materials you are cutting and having a proper blade for the rip or crosscut operation. Really knotty wood should be cut with a finer tooth blade. It is the feel for knowing what is required to cut material with unpredictable density is a hard thing to estimate and a hard thing to teach. I've see more than one workpiece thrown across the room. And the worker is always right in the line of fire.

Spence

[This message has been edited by SJorgensen (edited 09-29-2003).]

Carl
09-29-2003, 02:22 AM
Our school shop had a picture on the wall of a fellow with his left arm caught between two very large gears. It had pulled him in clear up to his armpit. I will never forget the look on his face...never.

T Wise
09-29-2003, 07:40 AM
Just another question on that table saw, it sounds like it has an automatic shut off if it senses it is cutting flesh instead of wood, this would be a good feature because most woodworkers I know didn,t realize they actually cut something important off until they tried to pick something up. I suppose if you had time to react it would be a good thing.

Evan
09-29-2003, 11:53 AM
I've been trying to figure out how that saw brake would work. Seems that it would have a low voltage system to sense the conduction to ground when flesh touches the blade. Then a caliper brake like on a car disk brake would be energized at the same moment the power is cut to the saw. It should be able to stop it in less than a rev. You would still be hurt but not missing any parts. I am not willing to test it.

darryl
09-29-2003, 12:58 PM
Wood is somewhat conductive, hence the operation of moisture meters, but the body is more conductive, so it's reasonable that contact with a body part could be sensed by current flow. It seems unlikely to be a reliable system, given the variables such as static electricity build-up from the materials being cut (what about plastic) and the belt running in pulleys. An induction motor doesn't have a built-in ability to be braked, so a caliper brake, as one suggested, might be part of the system. I'd sure wast to see it work fast, and no, I don't want to test it either.

Oso
09-29-2003, 01:52 PM
Induction motors brake pretty well if given a shot of DC on the stator windings. The higher the current, the more the braking.

I don't see the way it works either....seems like "digging a small signal out of a lot of noise". Conductivity is one reasonable way it could work.

But what if you are not touching the table, just the blade? Does their system still work?

Evan
09-29-2003, 01:55 PM
Yep, I figure it isn't in use because it likely isn't reliable. It's like the freekin chainsaw brakes and lawn mower brakes. What a PITA they are. I've been using a chainsaw for 40 years and aside from the one bite which had nothing to do with kickback I have not been injured. I've never had a saw kick on me. I've cut hundreds of cords of wood and felled hundreds of trees. I can drop a tree on a beer can. If you use the power tool properly you will not be hurt except in the rare event of some dangerous mechanical failure. Most of those incidents can also be avoided, like always standing to the side when grinding in case a wheel blows up.

docsteve66
09-29-2003, 02:01 PM
Stopping the saw? First I would try a spring loaded caliper with a trigger of some sort to stop the blade.
The real questiion is sensing the need to stop. Conduction? The operator wold have to be grounded (or at least part of the conducting path). Rubber soles, concrete floors would haveto be considered. The operator could not be assumed to have a body part on the saw table or frame. Capacity? A high blade would have more capacity in normal operation than a low blade almost being touched. Maybe the human body capacity when touching the blade would do it. Insulate the blade, makeit the center plate in a capacitor wherethe body is the third plate?

Should be easy to retrofit if it is capacity. Just insulate the blade, mount the caliper under the table.

Brainstorm it gents, and fastest mover makes a million! (or less). Good ideas are dime a dozen- its what isdonewith them that counts.

Evan
09-29-2003, 02:09 PM
Come to think of it, if something stopped my 10" radial arm saw blade that quick it probably would strip the gears right off. So now you have to design some kind of clutch as well as a sensing system that actually works reliably. It doesn't sound do-able.

wierdscience
09-29-2003, 10:37 PM
Too much safty makes for people dependant on safty equipment instead of common sense.
Grandpa always told me if I didn't feel comfortable with doing something on the job,then either do it different or don't do it even if they fire you,you can always get another job,but not a finger,or hand ,or life.Words of wisdom that have served me well.
The saw brake thing,I read the original article that appeared in FWW ,from what I remembered the device worked by the sawblade and its motor and mandrel were isolated from the rest of the unit,what the thing actually sensed is the potential between you and the blade,very minute but still there,it would then in a split second amplify that signal and send current to a nichrome filement which would over heat,melt and release a preloaded spring that propeled a plastic finger into the blade which would dig into the teeth and stall the saw instantly,it does work, the inventor demonstrated it with his own finger,he only got a little nick kinda like you would get in a blood test,lots better than picking fingers up off the floor.

Another word about safty,from having worked wood for years I can tell you first hand that the single biggest problem is that most people have no concept of whats sharp and whats dull.
A dull table sawblade conbined with a out of wack fence is deadly,kickback is the number one cause of lost fingers on tablesaws and joiners.
Its amazing how many people including machinists don't know what sharp is,in woodworking tools it means razorblade,nothing less.

GunnySnow
09-29-2003, 11:11 PM
Hello Guys,

I would like to suggest that I would have given just about anything to have been using one of those special table saws on July 25th of this year.

I was at work, making something for a jig for the shopbot we have there, and well this machine has no guards to speak of (not many saws have guards that stay on after a little while, seems everyone removes them) anyhow I have about 5 years experiance with this type of machine and have never had an accident.

Guess what? July 25th I had my thumb dragged through the table saw, while the blade was on a 45 degree angle.

I was able to shut the bugger off, and get someone to call 911 while I tried to keep from passing out. I lost major blood and was finally rushed to the hospital. I had emergency surgery within 5 minutes of getting to the hospital and recieved over 60 stitches had the thumb re-attached.

I had to have two other surgeries since then and its still ****** it is there which is nice but it wont bend anymore at the upper nuckle.

I am actually affraid of that machine now more than ony other I have ever worked on.

I will not work on one now unless it is fully guarded and even then I am not sure

Its amazing how fast it happens, it really is.

Hope everyone remembers these stories, makes you more alert.

And by the way, I know I was an idiot for using this machine unprotected, but you know, you get careless sometimes and it either bites you or it doesnt, I got bit.

Now I am preparred to make sure it only happens once.

Gunny

Oso
09-30-2003, 12:01 AM
I am questioning the thing still. I grant that it will shut off if you approach the blade slowly.

BUT, I notice that when stuff happens with a tablesaw, it happens quick, real quick.

I suspect that the blade would still take your finger off, and be stopped just about the time it exited.

At say 3600 rpm, that is 60 times per second. So each rotation takes about 16 milliseconds. One rotation is easily capable of chopping off a finger.

a finger approaching at 1 foot per second (slow) travels about a fifth of an inch (0.2 inch)per 16 millisecond rotation.

Lots of fingers are maybe 3/4 inch through. Therefore, even at that slow speed, in 50 milliseconds, your finger is about cut off.

If you have a sudden yank by the blade, which is what gets plenty of people, the speed could easily be three times that.

So if it takes more than 15 or 20 milliseconds to stop, it has done all it will ever do to cut your finger off. Even 5 milliseconds will be a serious chop, probably causing permanent damage and disability.

You should be able to THROW weiners at it and have it stop with just a nick.

If it can't handle that, it's expensive false security.

Worse, if legislated, it will stop development of something else that actually works.

Evan
09-30-2003, 12:18 AM
I agree

Thrud
09-30-2003, 01:08 AM
Oso:
Anyone that gets lax around powertools is an accident waiting to happen - even when fitted with the best safety devices it is still possible to get severe injuries. The whole point is to reduce the possiblity of injury. The only way to eliminate injury is remote operation with robotics and that is not going to happen for decades - although mining companies in Canada are already using remote control underground mining equipment.

[This message has been edited by Thrud (edited 09-30-2003).]

Oso
09-30-2003, 09:00 AM
BEANS..........

You know that and I know that, but Ms Congressperson has no clue, no more does Mr congressperson.

They just legislate whatever dumb thing is there.

Point being that like Kalifornia requiring a certain list of pollution control devices to be on a new lawnmower engine, they are legislating a method, not a result.

No other method can or will be developed then.

Plus, the various show-off demonstrations merely convince people that it is safe. No need to worry, it is safe.

That is a bunch of bull. it will make for as many or MORE injuries, and lots of lawsuits.

BTW, the law requiring the "safety" device will be no defence when the "safety" device is proven to be "inherently defective". Big awards of damages......

AND, the first person to cut moist wood(which they shouldn't do) will disconnect it pronto.

SJorgensen
09-30-2003, 01:51 PM
I don't think a system that is expected to sense that it is cutting flesh will work out very well for obvious reasons. Practically you will need 1/2 or a 1/10th of a second I would think. A system that senses by infrared something inside the cutting zone, say 1" from the side of the blade and a couple of inches in front. Or perhaps scanners could track the shape of the material being cut and recognize anything outside of the shape as a foreign object. Another more practical device might be a glove that is tracked by a sensor system. These gloves could be made for some old timers with three or four fingers, depending.

I don't want safety legislated into every aspect of our lives. I think personal responsibility and accountability is essential.
If I want safety features that look like a practical and helpful device I'll probably buy it.

There are some fairly safe cutting blade systems that I have seen that oscillate. In hard material it cuts very well but in soft fleshy material it can't cut. Still I like computer controlled devices. I don't think it is that far away. They could even be small, like a hand power tool that follows a pencil line. That would be cool.

Spence