I have read this thread several times and frankly, it has sent shivers up my spine. I am not standing in judgment of anyone or any process, but I have had first hand experience with rotating bars maiming or killing people. Plus, I have had a serious mishap on one of my own machines that cost a lot of money to repair.
Years ago, I was a field service engineer for a well known builder of multiple spindle automatic bar machines…screw machines if you would. These machines had 4, 6 or 8 spindles with a capacity from 9/16 to 6 inch stock, depending on the model of the machine and the number of spindles. After 10 years in the field, I was promoted to Product Service Manager and brought back to the plant. One of my responsibilities was to investigate any serious accidents on one of our machines anywhere in the country. I had a couple that I will never forget.
The first was in a factory in one of the southern states. They had a line of machines we had built. Most were 1 5/8” capacity with 8 spindles. These machines are usually equipped to run 12 foot bar stock. They have a stock reel that indexes with the spindle carrier, holding the 8 bars in line with their respective spindles. Each spindle has a collet closing mechanism and the machines run automatically, feeding stock, machining it and cutting a workpiece off every cycle. The stock reels are designed to swallow the entire bar length of 12 feet. Customers desiring to run longer stock would buy machines with longer stock tubes or retrofit what they already had. Some chose to do otherwise.
An operator had just loaded his machine with a fresh load of stock…stock that was too long and the bar ends were protruding out of each stock tube by a couple of feet. The man started his machine up and one of the bars started whipping and striking the other bars, causing them to bend and strike each other. Within a few seconds, one of the bars broke off and it went flying across the department, striking a female operator at another machine. It hit her in the head, fracturing her skull and killing her almost instantly. Once my company became aware of the accident, I was on the next plane out to investigate, take photographs and interview as many people as I could. The company where it happened had shut the area down tight after the woman’s body was removed. They didn’t touch anything, waiting for my arrival. It was a gruesome scene, with blood, pieces of hair and scalp and brains strewn about. I spent about 3 days there and returned with many pages of notes and over 100 photographs. All that information along with my report was forwarded to our corporate attorneys.
The next incident occurred in another southern state, near the Mexican border. That company had only a few old machines that were over 75 years old, but they were technically built by our prior owners. Over the years, my company had changed hands several times.
This accident was tragic as well. A young janitor was mopping the floor near the screw machines. It was a very hot day, so he had only his underwear on under his coveralls. One of the machines had rotating bar ends exposed, not much, but they were not covered by the stock tubes. He got too close to the machine and his coveralls were caught by the rotating bar. The machine indexed and his coveralls were ripped completely off, including his underwear…and his scrotum. A young 24 or so year old man, newly married, was maimed and would never be able to father a child. Some time later, I heard from the attorneys that the settlement was 7 figures.
Finally, after 18 years of working for a machine tool builder, I started my own screw machine shop. Eventually, as I grew, I bought a couple of new Mazak CNC lathes. Most work I did on them was in collets and I had a bar puller on the turret. I made urethane liners for the spindle for every stock size I ran. I saw-cut 12 foot stock into lengths that would be totally enclosed in the spindle. One day, I had an odd-ball length of 3/4 inch stock that stuck out maybe a foot. I thought I could get away with it.
I started the machine up and the spindle started to wind up to 6,000 rpm. Before I could hit the E-stop button, the machine started to shake and make horrible noise. Once it was shut down, I could see that the bar had bent 90 degrees and that piece broke off hitting the ceiling. The machine which weighed 7,000 pounds had actually moved a couple of inches. .
I was shaking with the thought of what could have happened. I unchucked the bar and removed it from the spindle. I opened up the covers over the rear of the machine and slowly jogged the spindle. I could see the chuck actuator was wobbling. Not good. I did some checks and found the spindle module had moved. It was time to call Mazak Service. They sent a service tech and he said the spindle was bent and couldn’t be repaired. The actuator was also damaged beyond repair. He undressed the machine and removed the spindle module, which he took back to Mazak Service Center. The machine was down for a couple of weeks. The cost of repair was over $8,000. My poor choice of allowing a bar to extend past the spindle was a frightening, expensive lesson. The worst part was, I knew better, but didn’t think it could happen to me.
I am going to make reference to this post in the Safety section. I believe there are lessons to be learned. Please, everyone be safe.
