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Looking for input on a recent tragedy

WVDAD1992

Plastic
Joined
Feb 19, 2018
Being a Machinist, I know that I would not chuck a 1/4 inch piece of steel unsupported more than. 1 to 2 inches from chuck. Now to current situation. Facility I work at has a lab, in this lab they have 2 ancient drill press that use a standard Jacobs chuck (never seen replacement nor inspection that I know of) the tech there use a 10 inch long 1/4 inch rod with a 3 blade agitator to mix samples. Recently a tech was using one and was adjusting rpm from 4000 down to 1000 as required by procedure. Having to use a hand held tach (kind of archaic). Shaft took to wobble, resulting in a 90 degree bend at chuck. Caught his hand and did major damage. Management is now in the investigation step and being a former machinist I had spoken up about the dangers of running something that long, that small, unsupported. Let alone in a 3jaw Jacobs chuck. Some of the engineers are adamant that it couldn’t have bent without him hitting it. That’s not my opinion. I’ve seen way to many things thrown out of machines or alignment do to centrifugal forces. I have searched and cannot find any materials to help my plant manager solve this issue or come up with a root cause. Sorry for the long post, but I thank anyone that took the time to read and would offer some insight. This tech is still in hospital and and any solutions I can offer may help save any future accidents from occurring. Thank you
 
All it has to do is be a bit out of balance/true (and everything is) and/or hit a resonance, and it's all over. 4000 RPM is very fast for such a thing. If it were a lathe running at that speed, I'd be nervous with more than 3" out of a collet. That's just gut feel, not sure if there are any rules or standards for such things. Having an agitator on the end just makes everything far worse. People do detailed analysis on this sort of thing- How fast can I run my mixer? What is the maximum RPM allowed? - Cleveland Mixer
 
10 inch long 1/4 inch rod

4000 rpm

then side load it with whatever glop they are mixing


yeah, that will do it


careful about costing the company a whole ton of money, shooting messengers and all

correct answer is probably along the line of, get an engineer to look at that, but be prepared to write a big check
 
my nephew had a similar thing happen while using my edge finder: ran up the mill without checking the speed (max is 4000) . smacked him on the hand a couple of times , before flying free

no permanent damage done , just soiled underwear and buggered edge finder.

bill
 
A few years back, I was drilling some deep holes. 1/4 dia x 23" deep. I accidently hit the spindle start without shifting the tranny into low. At only 2000 rpm, from the time it took to hit spindle start, to spindle stop (like maybe 1/2 second) the drill bent 90 deg out at the chuck. Fortunately there was nothing in the way. So what you describe is entirely possible, without it being bumped.
 
Some of the engineers are adamant that it couldn’t have bent without him hitting it.

Are these REAL engineers? Or are they "engineers"?
Even then, I've yet to meet an engineer that is anything but booksmart. Not saying they don't exist, but most think their way is the only way.
 
I have seen 35mm od shaft whipping around like it was made out of rubber, it went right by my head, a bushing failure in bar feed. We changed a lot to cure the problem from ever repeating.

All I can say is get a purpose build mixer, or make a bigger od hollow shaft for you existing one with support bearings.
Proper engineering with safety factors to do it right. It's just money to make it right.

Marko
 
Being a Machinist, I know that I would not chuck a 1/4 inch piece of steel unsupported more than. 1 to 2 inches from chuck. Now to current situation. Facility I work at has a lab, in this lab they have 2 ancient drill press that use a standard Jacobs chuck (never seen replacement nor inspection that I know of) the tech there use a 10 inch long 1/4 inch rod with a 3 blade agitator to mix samples. Recently a tech was using one and was adjusting rpm from 4000 down to 1000 as required by procedure. Having to use a hand held tach (kind of archaic). Shaft took to wobble, resulting in a 90 degree bend at chuck. Caught his hand and did major damage. Management is now in the investigation step and being a former machinist I had spoken up about the dangers of running something that long, that small, unsupported. Let alone in a 3jaw Jacobs chuck. Some of the engineers are adamant that it couldn’t have bent without him hitting it. That’s not my opinion. I’ve seen way to many things thrown out of machines or alignment do to centrifugal forces. I have searched and cannot find any materials to help my plant manager solve this issue or come up with a root cause. Sorry for the long post, but I thank anyone that took the time to read and would offer some insight. This tech is still in hospital and and any solutions I can offer may help save any future accidents from occurring. Thank you

procedure sucks. He should have adjusted the speed to below 1,000 rpm BEFORE ever putting the agitator in the chuck.

also, un-gineer is dumbass. calculation of this sort of thing must always assume there is initial imbalance because nothing is ever perfect.
 
10 inches long x 1/4" diameter!!!!!!!!!!!!!!!!!!!

That's a length 40 times the OD. It was an unsafe practice from day one and IMO shows incompetency in management. It would be bad enough for one-time use but as a regular practice and one that apparently had a procedure to follow there's just plain no excuse.

At a minimum the operator should have been separated from the process by a protective shield and if they need to mix things regularly they need a dedicated tool designed for the job.

I always hate to hear stories like this and hope the poor tech won't have permanent impairment. As a youngster I nearly lost a thumb to an unsafe cutting practice I had been ordered to do despite expressing concerns about safety.
 
Seen it happen with un supported bars sticking out of the rear end of a lathe spindle three times in my working career.

Last time I was working as the stand in overhead crane driver. In the corner of the shop was an " Elliot Omnispeed " tool room style lathe that was used by all and sundry in the shop. While I was watching what was going on down below I saw one of the fitters putting a length of roughly 7/8" bright drawn bar into the chuck with about 3' 6" stuck out the back. The guy didn't check the spindle speed and unfortunately for him the lathe had been left in top speed.

As I saw him about to switch the lathe on I was shouting " No, No, No," but he couldn't hear me above the noise of the shop.

After a second or two the bar started to wobble and within a second or two it had bent at 90 degrees like a big Allen key and it was beating the ground at the rear of the lathe.

The force lifted the headstock end of the lathe off the ground about 3". That meant pulling 4 X 5/8" Rawlbolts out of the ground ! Luckily the fuses blew because the guy just ran away.

Tell your boss that story if they doubt you. That was a real incident that I had a birds eye view of. I have seen and heard the bang in two other incidents just like that when bars have bent in lathes. It all happens in a flash !

Regards Tyrone.
 
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That is the worst thing about this game, there are so many things that can hurt you,
and a lot of them you don't even realize until they bite you...

I still run into things that bite me.. "Ooooh.. Never got hurt like that before"

There are a million ways to idiot proof this particular operation, and some of them
may be expensive, and some not so expensive...

Sticking with the current method, I'd go get a POS drill press, step pulley style and
mill or turn off any pulley combination that would let it go over 1000 rpms. Then
I would beef up the shank a bit.
 
That is the worst thing about this game, there are so many things that can hurt you,
and a lot of them you don't even realize until they bite you...

I still run into things that bite me.. "Ooooh.. Never got hurt like that before"

There are a million ways to idiot proof this particular operation, and some of them
may be expensive, and some not so expensive...

Sticking with the current method, I'd go get a POS drill press, step pulley style and
mill or turn off any pulley combination that would let it go over 1000 rpms. Then
I would beef up the shank a bit.

Why not just BUY an OSHA approved mixer designed & built to do whatever the OP
was trying to do.
 
How far off-axis to you figure the farthest point from the chuck was to start? 0.005"? Naw, that's too perfect. 0.0625"? Getting closer. 0.125"? Sounds like more of a minimum. Now, I don't have the license to do the sort of math to calculate centrifugal force, but I can sure as hell assure you I wouldn't start spinning it at 4k RPM. At least, not while standing anywhere near the path of destruction.
 
Id start with was the mixer "Homemade" or store bought. If store bought there could be a RPM limit. Not much but its a start. He was doing as told so bumping would be something inevitable. Totally disregarding Rpm limits is all on them
 
Some of the engineers are adamant that it couldn’t have bent without him hitting it.


If the "engineers" really said that, they are fucking idiots. They need to STFU before they further damage the chances of management making things right and rectifying the situation with their deficient equipment. The victim of this negligent equipment choice is already probably damaged for life and may never have full use of his hand again.

Way back, when I worked in a very large shop I was elected by the guys to be the safety rep, and saw all sorts of shit like this that could/should have been avoided.
 
Likely a blade touched the side of he container and then the weight of the container bent the ¼ rod..stupid set-up for sure..blade should have been going 300 or less and been a thicker shaft..

Not to hack the OP so don"t discuss this here but one of my past Boy Scouts was splitting logs with his grandfather using a power-splitter and almost got his hand cut on two..Good rule to follow and tell is load a splitter with hand on the OD of the log and never at the ends. This to Keep hands out or the danger zone...The boy was studying to become a pilot and not if his hand does not function properly he will never become one..
 








 
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