Machining confession thread.

[nlancaster]

I have been running wire EDM machines in a production environment for 5 years.
We run a part that is a titanium/ceramic glue up, and we have to align it to the wire axis to .0001 or better.
We use a gauge pin thru the center bore for this alignement.
In my first year I crashed the lower head into the gauge pin because I forgot to remove it. $2k part broken.
Last month I did the same thing, but now we are charging $5k for the same part.....

 

[jim rozen]

"Many years ago, I banged a chick on the workbench next to my lathe. "

I've christened a few labs here back in the day - but it was with my wife.

Does woodworking count? One night I was going to shorten up my bench to make it fit in a tight spot. We have a big milwaukee circular saw with a carbide blade on it. Backstory: I had lent it to another mechanic to cut down some panels that were galvanized steel cladding on both sides of particle board - these were RF screen room panels. He had put the blade on backwards to go throught he galvanized clean, never put it back the right way.

And I didn't check before starting to cut. I did however, put on some safety glasses and a face sheild, as I was working alone at night. "Damn this thing doesn't cut well" as I really had to push hard get it to cut. Finally made it through, looked up and the entire hallway was FULL of smoke. I had friction-sawed my way through 2" maple. The smoke detectors had gone off so the boiler room guys showed up, and I explained what I had done. "Hey, yer supposed to turn that thing ON before you chop your way through the wood!" Nowadays they'd fire my ass for doing something dumb like that. The blade had even spit off a few of the carbide teeth. Not good.

 

[Bill D]

My father said one of the machinists at the lab had worked for caterpillar turning big engine flywheels. He messed one up. too small. Rather then turn in the bad one and get a new, and be dinged for wasting time and material, He turned it down, during lunch, to chips so no evidence was left except for an extra 200-300 pounds in the scrap bin.
Bil lD

 

[hmw1972]

That reminds me of another one.
I had the job of replacing the cross slide leadscrew and nut on a big “ Craven “ lathe. I took out the old screw, measured everything, made a drawing etc. Then my drawing was sent out to “ Halifax Rack And Screw “ for them to make the screw and nut.
About a week later the new screw and nut came and I fitted the pair. I finished just before the night shift came on and I had a brief chat with the operator, then I went home.
When I came in the morning the guy was stood by the clocking in machine. I said “ How did you go on with the new screw and nut Kenny ? “
He said “ Fine, but what I can’t understand Tyrone is when I put a 0.200” cut on it only takes 0.100” off ! “
After about 5 minutes it dawned on me - the old screw was a two start thread and I’d never noticed ! I’d made the new screw a single start !
We had to have another new screw and nut made and I swapped the old/new one out.

Regards Tyrone

Hello Tyrone,

My Broadbent-Schofield lathe has a two start thread on the cross slide leadscrew. It also has an indirect reading dial on that leadscrew and each graduation is .002", meaning moving the dial one graduation reduces the diameter by .004" (pretty coarse). The screw is in decent shape but the nut is worn out. I was thinking if I made both new it would be a single start thread which would then make the dial direct reading and one graduation would reduce the diameter by .002". It would be just like you did but I wouldn't change it.

Ken

 

[GregSY]

This is not a pure machining mistake, but when you make an electric motor, the stator is stacked of many thin laminations of electrical sheet steel. It's called electrical steel for it's properties but mostly because it's coated with a thin layer of insulation on both sides....the purpose is to not have conductivity across the laminations.

See photo....this is a typical stator and you can see the slots which hold the coils. Be sure to make note of the color of the laminations...

So about 20 years back.....high voltage (13.8KV) stator was being made for a 15,000HP 327RPM motor. As it turns out, one of the winders had been using a Starrett 6" steel rule which fell into the bottom of one of the slots, lying flat. No one noticed - because it's the same color as the laminations - and the stator was fully wound and VPI'd. Looked great.

Only, when they put the motor on test and poured the 13.8KV to it, the rule shorted out 6" worth of the 30" core and molten steel puddled into the bottom of the motor frame. About a $500K oopsie.....

 

[mkd]

"Many years ago, I banged a chick on the workbench next to my lathe. "

I've christened a few labs here back in the day - but it was with my wife.

Does woodworking count? One night I was going to shorten up my bench to make it fit in a tight spot. We have a big milwaukee circular saw with a carbide blade on it. Backstory: I had lent it to another mechanic to cut down some panels that were galvanized steel cladding on both sides of particle board - these were RF screen room panels. He had put the blade on backwards to go throught he galvanized clean, never put it back the right way.

And I didn't check before starting to cut. I did however, put on some safety glasses and a face sheild, as I was working alone at night. "Damn this thing doesn't cut well" as I really had to push hard get it to cut. Finally made it through, looked up and the entire hallway was FULL of smoke. I had friction-sawed my way through 2" maple. The smoke detectors had gone off so the boiler room guys showed up, and I explained what I had done. "Hey, yer supposed to turn that thing ON before you chop your way through the wood!" Nowadays they'd fire my ass for doing something dumb like that. The blade had even spit off a few of the carbide teeth. Not good.

I had a similar experience, but all was setup well with the saw. New boss sent me into the yard with a heavy worm drive skil saw to whack a hunk of aluminum off a 3 inch thick plate. With massive apprehension i trot my butt out in the pre-dawn hour and get to work. Between the smoke, sparks and near lack of progress, i gave up pretty quick.
When reporting to boss that all the teeth were knocked he confered with a colleugue who was equally dismayed and confused.
It was a slab of invar not 6061.

 

[hmw1972]

At the gas turbine overhaul shop I used to work in we had an LM1600 engine that had just been assembled. They are built vertically with the compressor facing upwards. One of the mechanics leaned over the intake to have a look and change fell out of his shirt pocket and into the compressor. It sounded like a game of 'Plinko' as the coins bounced between blades and stator vanes on their way down. Besides the obvious, the worst part was he had no idea how much change had fallen in. Because of this you could remove every coin you could find but never be sure you got them all. As it was worth several million dollars the entire engine had to be disassembled and every part inspected for coins. The forman came up to the guy, put one hand in each shirt pocket and with one swift yank, ripped both pockets off his shirt. We rode him about that for a long time. Ken

 

[???]

We used to run tiny little silicone injection molds in a Okuma with .15mm cutters overnight. Before we started the cut we would warm the machine screws and spindle up by programming a move diagonally across the table. I was working the late shift and the other tool maker set the machine up and went home. I took a look in the machine and the spindle was below the vice and about to crash into it. Stopped the machine and left a note. Should have left it running because the guy was a prick and would have deserved being fired.

 

[dstig]

"Good Judgement comes from experience. Experience comes from Bad Judgement"...

 

[Georgineer]

At the gas turbine overhaul shop I used to work in we had an LM1600 engine that had just been assembled. They are built vertically with the compressor facing upwards. One of the mechanics leaned over the intake to have a look and change fell out of his shirt pocket and into the compressor. It sounded like a game of 'Plinko' as the coins bounced between blades and stator vanes on their way down. Besides the obvious, the worst part was he had no idea how much change had fallen in. Because of this you could remove every coin you could find but never be sure you got them all. As it was worth several million dollars the entire engine had to be disassembled and every part inspected for coins. The forman came up to the guy, put one hand in each shirt pocket and with one swift yank, ripped both pockets off his shirt. We rode him about that for a long time. Ken

A chap I worked with told me that when he was an apprentice he was working on a turbine overhaul and dropped a feeler gauge down into the bottom of the main casing. He had the presence of mind to make a chalk mark against the row of blades it had fallen down and reported it. They fished for the feeler with wires, magnets and anything else they could think of, and eventually had to give up and lift the rotor out. They found the feeler all right - in the row next to the one he had marked.

George

 

[hmw1972]

In my old shop I had only single phase power. I ran my machines off a rotary phase converter that was fed from my main panel by a double pole, 100 amp breaker. The instructions from the manufacturer of the phase converter stated that if you were going to do anything to it you had to shut the breaker off and then short across both terminals of the single phase supply (i.e across the 100 amp breaker) to drain the capacitors. Failure to so so could result in a serious jolt from the capacitors. I kept a piece of No. 6 wire bent into a u shape for shorting out the terminals. One day I went to check something in the phase converter and dutifully shorted out the terminals, having first forgot to shut the breaker off. Fortunately the shorting wire had insulation on it so I am still here to tell the tale. My face was about 18" from from the terminals and I had no safety glasses on. The molten aluminum that had once been a set of terminal blocks burnt holes in my shirt and left burn marks on the top of my desk, which was nearby, however nothing hit me in the face. After the smoke cleared and I finished shitting out several horseshoes, I got on the phone and ordered two new terminal blocks from the phase converter manufacturer. Ken

 

[mark costello]

Drilling 2 "O" ring blocks that get welded to stainless tubing. 4"x4"x1" size. All done,hand Them to the boss and He says" which one has the tapped holes?"
Given a 3"x2' or so shaft to press into a block a couple of inches inches thick. Both parts made by old timers that never made a mistake. Got the shaft about 1/2" deep with a .030-.040" press fit before just about stalling a 50 ton hand hydraulic press. Good thing it was not electric. First couple of months as a brand new apprenticeship. It was MY fault?

16" OD x 24" long piece of Aluminum with a 2" stub shaft for a locking nut for a grinding fixture. Used wrong axis 90 ° off for threading. Never did that again in 29 years since, so I learned the hard way.

 

[rons]

"Good Judgement comes from experience. Experience comes from Bad Judgement"...

When you start out in life and take the path of "wise guy" the journey to "wise man" is a long one.

Connect the rectified DC V+ to the AC line on a VFD and see what happens.

 

[DouglasJRizzo]

I had a similar experience, but all was setup well with the saw. New boss sent me into the yard with a heavy worm drive skil saw to whack a hunk of aluminum off a 3 inch thick plate. With massive apprehension i trot my butt out in the pre-dawn hour and get to work. Between the smoke, sparks and near lack of progress, i gave up pretty quick.
When reporting to boss that all the teeth were knocked he confered with a colleugue who was equally dismayed and confused.
It was a slab of invar not 6061.

Years ago, I knew a guy whose family owned a lumber yard. He told me of one of the yard hands that had taken the huge Skil circular saw and attempted to cut through a piece of CRS-1018. He made it through, although the blade looked like it had been through two world wars.