What was the dumbest machining mistake you ever made?

I just pulled a pretty good one. A customer brought in a GEW 98 Mauser action that had been re-barreled to a 9.3x62 with an unknown brand, lightweight, fluted, stainless barrel. He just wanted the stripper clip hump removed and a set of Leupold bases installed. I set my mill up with a chuck and was drilling a pilot hole with a 1/16" bit which, right before I reached my desired depth, snapped. I tried every trick I knew to get all of the pieces out of the hole, but every time I'd try to open up the hole, it would just wipe out the leading edge of the bit. I ended up chucking up an oddball .080 end mill that I had in my box to chew up the bit and then, my wife called me. I forgot where I was at and started drill while watching my depth gauge. All of a sudden, I lost pressure on the handle. Sure enough, I'd gotten distracted and forgot to re-zero my gauge after switching from the last bit to the end mill and ran the end mill all the way through the barrel shank into the chamber, so now, I'm shortening, threading, and rechambering the barrel for free.
 
I was drilling a pilot hole thru the floor from below to run an air line. I took some measurements off the walls but forgot about an extra closet upstairs so I was 6 feet off. I kept drilling and checking and drilling but I couldn't find the hole upstairs. When I realized my mistake and remeasured I still couldn't find the hole. I moved a table to get a better view and saw some sawdust under the leg. The table leg was 1 1/2 inches in diameter and I had drilled four inches straight up into the bottom of the leg. The hole was dead center.
 
I was making target stands and I had cut/made the parts which now needed to be MIG welded. A friend was watching and I was explaining how I liked to be up close to the MIG gun so I could see the puddle and advance it. I started with a one inch bead and didn't switch on the auto darkening helmet because I was explaining the process. My eyes were about 4 inches from the arc when it was struck...now here's the stupid part...I didn't realize immediately that the auto darkening wasn't on and finished a small bead. I had to think "Damn, that's bright" before I understood what was happening. Fortunately, no long lasting burns or damage although I saw a bright spot in my field of vision for about 4 hours. All I can say is it's a mistake you'll only make once.
 
Accident or mistake?

Mistake, trimming customers provided stock to the wrong length. I get it out, mark four 8" segments. Cut out the first, then accidentally cut one to 6". Come to find out (after improving my French quite a bit) that the plans said 6" not 8''. What a relief! I never told him :jester:

Accident, drill press vise sucking up and autofeeding a bushing in half a second. Scary!
Accident, drilling a piece of hickory in the drill press, 1000 rpm, with screw autofeed spade bits. Grabbed it from my hand and whacked my hand It felt like I broke it in every possible place.

I put that spade set away.....I actually do not know where they are now. Good.
 
Sort of machining, I was in the finishing stages of polishing an 8" mirror for a telescope.
It was going very well on the machine I had made for the job that has 1 motor for the platter and another motor for the eccentric drive to swing the polishing pad back and forth across the glass.
The drip feed was feeding the right amount of compound onto the surface and after watching for an hour I decided to go up stairs and make a cup of tea.
Put the kettle on when I heard the huge crash.
The drip feed had blocked, the polishing tool stuck to the mirror and the eccentric flung it right across the shop floor onto the concrete at high speed.
Took out a huge clamshell chunk from the edge to almost the middle of the glass.
3 weeks work totally ruined.
What surprised me the most was my complete lack of bad language, very unlike me.
 
Andre said:
Accident or mistake?

Mistake, trimming customers provided stock to the wrong length. I get it out, mark four 8" segments. Cut out the first, then accidentally cut one to 6". Come to find out (after improving my French quite a bit) that the plans said 6" not 8''. What a relief! I never told him :jester:

Accident, drill press vise sucking up and autofeeding a bushing in half a second. Scary!
Accident, drilling a piece of hickory in the drill press, 1000 rpm, with screw autofeed spade bits. Grabbed it from my hand and whacked my hand It felt like I broke it in every possible place.

I put that spade set away.....I actually do not know where they are now. Good.
Click to expand...

The mark of a true craftsman, is to screw up a job and make it look like it was supposed to be that way.

Somebody mentioned above that drill presses are evil, I have to agree.
 
Need I say more? FYI checking the depth of cut without shutting off the motor on my horizontal mill can suck in your finger. Cut down to the bone.

finger cut 1.jpg
 
Metalmann said:
Yeah, I've seen those engineers do some crazy stuff. They should definitely stay off the shop floor.

And, they Never admit when they're wrong.
Click to expand...

<begin soapbox> & off subject - sorry.

Actually I have to kindly disagree with the 'stay off the floor'. They actually should be required to learn how to 'crank' the handles
and operate the machines in order to know precisely what is possible and what is not.
A lot have no concept of reality when it comes to designing and tolerancing and *GADS* assembling the final product.
I started out in 1979 as a 'Tool Designer' under the tutelage of a very kind gentleman with close to 40 years experience.
He stated that he wanted to teach, train and pass on knowledge. The two tool and die makers under his supervision had
a combined total of 74 years. If only I had been a tad smarter and had my head in the right place. . .
That and if the company hadn't gone down as so many have in the rust belt.
I wish that I had be able to get more time on actually cranking handles. But it was a Union Shop and I was classified as 'Staff'.
However a lot of the old timers passed on quite a bit of info that ignited the desire in me to make chips.
Too bad apprenticeship programs went the way of the dodo bird.
<end soapbox>
_Dan

- - - Updated - - -

Back on subject.

"What was is the dumbest machining mistake you ever always made"
Has to be going into my shop and actually believing that I have the knowledge, talent and the touch to create something.

_Dan
 
This wasn't my mistake & there was no excitement involved but something that the a screw machine operator shared with everyone who passed by in the machine shop at a factory I worked in back in the 1970s. It seems that someone wanted like 24 small locating pins made up so that person procured the round stock & sawed every piece to length & put them all in a plastic envelope with the sketch for the pins instead of supplying one long piece of stock so that the operator could make each pin, cut it off with the parting tool when done then feed in the stock for the next pin, the way these parts are normally made.
 
Not the dumbest but the first one I was paid for and an odd outcome, straight out of machine shop class a few of us got on at a local foundry/machine shop, the job I was put on was machining center plates for rail cars using two boring mills, the mills where in horrendous shape, one side was done on one, taken off flipped and the other side done on the other mill.
One side was 1/16 tolerance and the other was an 1/8, I was give my 7 1/2 minutes of training and left on my own.
Second week there and on back shift I had one with extremely bad porosity, I took a large cut trying to get under it but as yet was unaware the a carbide bit could get sucked out of the tool holder, I made what looked like a giant shallow funnel.
So off to get the guy that trained me, he comes and looks and says yup it's !?%$ed do you want to take it home or take a walk to the river.....?
After seeing the confusion on my face he says it's like this " they have no true count of how many of these center plates there are, so if one goes missing no one is the wiser but if the foremam sees what I did I'll be fired so it's best if it disappears" then he goes on to say " I don't need any more at home so if you have no place to bury it at your house we carry it to the river" so I say I guess it's the river but I'm thinking what in the ?%#! are you doing dragging these 150lb plates home for..?
So on the walk to the river to dispose of the evidence he tells me for years he's been dragging the ones he screws up home and filling an old hand dug well but the well is filled and since then he's just been throwing them in the river...!:lmao:
 
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