Biggest Machining Mistakes
Biggest Machining Mistakes
(OP)
One of the self evident risks in manufacturing overall is as you assume more resposibility, you have the opportunity to make much bigger mistakes.
I'd like to hear about any mistakes/mishaps that members are willing to share. We'll have a laugh of course, but hopefully we'll learn something as well.
I'll start the ball rolling:
Worst Mistake: Sending air hardening steel shafts (15" dia) away to be heat treated with the old heat treatment specs which called for a water quench. I could fit my hand in the quench crack. Learning experience - a change can be a good thing, as long as you follow through properly.
Mishap: Bench grinder wheel exploded while I was using it. Fist sized piece of aluminum oxide ricocheted off the back of my hand and hit me in an area that is usually meant to be treated with the greatest of tenderness. Learning experience - welding gloves and apron may save your ability to have children.
I'd like to hear about any mistakes/mishaps that members are willing to share. We'll have a laugh of course, but hopefully we'll learn something as well.
I'll start the ball rolling:
Worst Mistake: Sending air hardening steel shafts (15" dia) away to be heat treated with the old heat treatment specs which called for a water quench. I could fit my hand in the quench crack. Learning experience - a change can be a good thing, as long as you follow through properly.
Mishap: Bench grinder wheel exploded while I was using it. Fist sized piece of aluminum oxide ricocheted off the back of my hand and hit me in an area that is usually meant to be treated with the greatest of tenderness. Learning experience - welding gloves and apron may save your ability to have children.
LewTam Inc.
Petrophysicist, Head Stockman, Gun Welder, Gun Shearer, Ski Instructor, Drama Coach.





RE: Biggest Machining Mistakes
Learning experience - Assumption is the mother of all...mistakes.
Colega
http://www.corporacioneg.com
RE: Biggest Machining Mistakes
RE: Biggest Machining Mistakes
My young peer, not given to taking instructions that he did not know the reasoning behind, began one day to use an impact wrench to chase the threads of a larger bolt in and out of a threaded piece to lubricate and free up the threads.
As he turned the piece counterclockwise, backing the threaded shaft out, he pulled the impact wrench away from the head of the bolt, and the socket slipped off.
I heard a resounding 'thwack' from his area of the shop, the operation he was doing being a very common one, and no one was paying much attention to his activity otherwise, to see him stagger away from his work, free hand to his forehead, with blood streaming from between his fingers.
The socket, with all the possible directions that it could have gone in, came off the universal as it turned 90° and struck him in the forehead. He has a scar to this day. It took several stitches to close it. I vicariously learned a valuable lesson from his mistake.
rmw
RE: Biggest Machining Mistakes
First one that comes to mind, I saw a guy take a Case Harderned 48"x 1.5" x 2" bar (cut on one side like a flight of stairs in .125 steps w/ 7Degree angle to them)... anyway he took this hardened bar and was getting setup to finish grind it. He checked the flatness on a surface plate and it was bowed in the middle. So he put it in a manual press and tried to flatten it. Needless to say it popped shortly after he put some pressure on it, snapped the part like a toothpick. I kept a 4" piece of it, it now serves as an example of case hardening for me. You can see the shell all aournd the outside of the profile and the center looks powdery.
Maybe I'll come back with some more later.
Fill what's empty. Empty what's full. And scratch where it itches.
RE: Biggest Machining Mistakes
60 pieces of scrap. Lesson learned the hard way.
RE: Biggest Machining Mistakes
Colega
http://www.corporacioneg.com
RE: Biggest Machining Mistakes
RE: Biggest Machining Mistakes
RE: Biggest Machining Mistakes
gun
adjective:- to be gun at something is to be very good or the best at something , e.g.., a gun shearer is the best shearer.
May be taken as a slight a slight exageration on my part.
LewTam Inc.
Petrophysicist, Head Stockman, Gun Welder, Gun Shearer, Ski Instructor, Drama Coach.
RE: Biggest Machining Mistakes
The result? A whole bunch of expensive high performance staninless steel alloy parts scrapped, and worse, a very tight shipping schedule shot all to hell.
RE: Biggest Machining Mistakes
Some winters ago, working at a shop in Denver, I was moving a part from one machine to another on a HMC cell center. The tool matrix were all virtually the same with a few exceptions. Well, the program called for a 1/2 em which spun at 14k, the magazine had a 7/16 gundrill (11.0" gage length) in it. Imagine my surprise when that gundrill fired up to 14k. I slammed the door shut, and before I could hit the E-stop, the drill snapped and shot through the roof of the machine. Found the shank on the floor next to me but never did find the carbide end.
That spring as the snow began to melt, we noticed the roof leaking over the machine. A maintenance guy went up there to fix it, and you guessed it, he found (on the rooftop) the carbide end of the gundrill that broke a few months prior.
RE: Biggest Machining Mistakes
One that I was involved in was a PV head with a 60" bolt circle. We had put an new flange on the vessel and a very obstinate design engineer had designed a new head and supervised its fabrication and machining of site. When the head arrived on site I ask if he would like our group to verify the dimensions, in short answer NO!. We had insulted him. The head was brought to vessel for installation and while hanging on the monorail I noticed the bolts that held the protective cover on were in a odd position, but didn't say anything. The cover was taken off and swung into position and as a mechanic was set to install the top bolting he turn and told the designer there is no hole on the vessel flange. He had one holed the head while body flanged was two holed.
We manufactured in house 8" x 1l" 1" thick SS extrusion dies for extruding synthetic fiber. A particular type die was supposed to have 1280 holes equally spaced in two sets. Even though the holes are manually drilled the position is set with an xy table. For some reason they number of positions were only 638, this included both the back and front side. Some one counted the holes in a set and revealed the problem. The operations group rejected the lot dies (50) due to the missing holes. The cost of dies was in the neighborhood of $35,000 at the time. The manufacturing group work 24/7 through the holidays making new dies.
I put a rejected die on a comparator and compared the pattern with one that had been in service for several years, all the same. The rejected dies were slipped into the process one at a time over several years.
The biggest one was an expander wheel made from an A286 forging. The block was forged, skinned machined, and tested. After this it was sent to be rough machined and tested again. At time it was sent to rough out the blades. It was then shipped to the final machining. About half way through the final machining one of our engineers on vacation stopped by to see the machining process. To his astonishment they were machining a wheel with the wrong hand. A the time it was a $150,000-$200,000 mistake. I never heard the final resolution of problem. The wheel went to scrap in 2000.
RE: Biggest Machining Mistakes
It's something I really keep in mind today, and I've been able to climb down off my smart horse before I make a fool of myself a few times.
LewTam Inc.
Petrophysicist, Head Stockman, Gun Welder, Gun Shearer, Ski Instructor, Drama Coach.
RE: Biggest Machining Mistakes
The piece of steel, with a sizable indentation and clear fingerprint pattern, is passed around during safety training. It gains the students' attention.
RE: Biggest Machining Mistakes
t a high dollar loss, but what was significant was that there was a potential for a serious injury ( to me!!!) which luckily didn't happen. We had an order for a shaft (I forget the mat'l grade, 1144 range maybe) from a wire manufacturer which included shrinking a hardened D2 toolsteel sleeve on a center portion of the shaft. The sleeve dimensions were approximately 8" ID x 10" OD x 15" long. The only part of this job I was given was to cut the sleeve OD to within .005 of finish size to prepare for grinding and polishing. (after it had been installed on the shaft) I forget how much mat'l. had to be removed, but it wasn't much, maybe .020. Well, I made the cut and was within 1/8" from the edge on the 15" long sleeve when without warning that nice pleasant spring day was shattered along with that D2 sleeve! That sucker absolutely exploded apart and sent shrapnel everywhere! The customer had sent the prints including dimensions and amount of interference between sleeve and shaft, which I would say were right on the money. The problem was the shop had a qc guy that inspected parts before going out the door, but failed to inspect these parts before assembly, which was a mistake. We later found the error must have been in the sleeve....the shaft size was correct. The lesson I learned....always be very inquisitive, especially when following up on someone else's work.
RE: Biggest Machining Mistakes
"Supposed to make the opposite dash number - not the as shown dash number"... if I had a dollar for everytime I've seen that one.
I've seen this in parts valued over $100k. Hopefully the vendor eventually buys the other dash.
--
Bill
RE: Biggest Machining Mistakes
'common'
'mistake'
'aerospace'
LewTam Inc.
Petrophysicist, Head Stockman, Gun Welder, Gun Shearer, Ski Instructor, Drama Coach.
RE: Biggest Machining Mistakes
I agree with you but I don't see how a plane could fly with (2) left hand wings or anything else.
Go to a fab shop and ask the pressbrake operator how many times he has bent the part the wrong way and made the wrong hand part.
RE: Biggest Machining Mistakes
Nick
"Speed costs money boys, how fast do you want to go?"