What was the dumbest machining mistake you ever made?

Back in the early sixties I had just started working in a T and D shop. My leader assigned me to mill the 1 1/2 chain slot on some cast iron counterweights to be used for a large vertical drilling machine being fabricated in the shop. The counter weight plates were about 1 1/2 thick and 16 inches square. I had to lift them heavy plates up onto the x/y table (36 in high) of an old WW2 production Cincinati vertical mill. I had never run one of these beasts before so the lead hand gave me a short operating lesson. It went like this: This is for this, that is for that, cutter goes in this way, stop, start, feed right, feed left, etc. Well, I clamp the counterweight onto the table and position the cutter to cut the slot and start her up. Engage the feed and start to mill the slot. As I watch the machining I notice the cutter seem to be moving up into the collet chuck so I stop the machine, clear away the chips and low and behold I find the cutter has some how cut its way into the top of the milling machine table. Nobody had told me that the knee feed was in the up position....................... The Tool Shop owner was not happy.
 
This one isn't mine but a friend just told me about his:
He just finished a 1 1/8 left hand external thread on his lathe. He didn't have time admire it when he knocked something off the compound rest and it hit squarely onto the on lever started the machine and drove the tool into the piece ! very unhappy camper !

Me : I bored a hole to fit a 240mm bushing so that it would have .4mm "crush, my brain had a fart and I bored it to the bushing size ! Luckily I saved the job by welding the bore back to under size and started again.
This time with the final size tattooed into my retina's.

As long as we as machinists don't get hurt that's the main thing :phew:
dd
 
Surprised no one has mentioned doing something similar. Had a grinding fixture to make from 14" OD Aluminum. It was to hold rubber rings stacked together to be ground about 25 at a time. The end cap to compress the stack was 2" OD and threaded to use a cap off another fixture. Welllllllll all I can say is I will ALWAYS from then on remember which axis to set the threading tool on, as 30 degree threads just don't seem to work as well.:nono:
 
Oh boy... Hate to admit this but, I've cut one or two parts backward on the mill by having the 2D drawings on the table behind me, looking at them and forgetting to transpose the orientation. This is a clear sign of working while not being focused or being distracted and it should serve as a wake-up call that it might be time to pull your head together or get out of the shop for a spell.


Ray
 
My dumbest machining mistake?
To show wifey the drill press can be used to turn small plastic parts :bawling:
 
twowheelinjim said:
At work we have a huge Cincinnatti horizontal mill. When i joined the company it was deemed innoperable due to electrical issues. I later found out the elctrical issues meant that the plug socket where the DRO plugs into was bad. The machine itself ran and the DRO could be used if one pulls an extension over and plugs the DRO in. The real excuse for being down was people were afraid to run the thing....So as a newby I got tasked with cutting keyways on a 6''X22' shaft on this mill. No problem, I have used smaller machines like it in the past so I gave it a go. So I set it up and strapped the shaft down to figure out where to place the clamps etc. I get ready to cut and get pulled away for a second. Before I walked away I started the spindle and turned my back. I figured I would idle the spindle before applying cutting pressure. I knew the X feed was off but didn't realize the Z feed was engaged. The lever is right to the power feed. Another machinist saw what was happening but froze as he was scared to death of this machine. The cutter plowed into the shaft and melted into it about 1/4'' . The cutter actually stuck out of the BT-50 collet about 2 1/2'' but by the time I got to it, it was barely 1/4'' sticking out. The actual collet was rubbing to the point it pushed the shaft off the clamps. This machine is very powerful and stout... Luckily I had decided to use a cutter that used two carbide inserts and it was not the bottom cutting type. I thought for sure I killed the shaft and the collet but to my surprise, I was able to remove the remains of the cutter and clean up the collet. As for the shaft it required a bit of welding and grinding to remove the boo boo. There was a potential of $12,000 loss for the shaft plus I have only been working for about two weeks when this happened. This was last week by the way. I have six more shafts to cut so I have taken the liberty of cleaning the areas around the levers and marked them with a sharpie to get a better visual of where the controls are; at least the neutral positions. I was later told by one of the weldors that no one else wanted to run this machine because they were scared of it. As simple as this machine is, it could easily make a hot mess in a hurry if gets away from you in a second. Now I kind of enjoy running it and it will be even better when I make a jig to cut keyways on it. Hopefully once it's properly set up others won't fear it and try to use it.
Click to expand...

I can relate to this. When I was an apprentice many years ago I was given the task to machine an undercut bearing surface on a 6" boat prop shaft. Keep in mind the shaft was about 20 feet long and material was Monel; a very expensive piece of material! I was making .100" passes to reduce the diameter when lunch time rolled around. Not thinking when I started the job up again I didn't measure to determine where I left off and made one too many roughing passes. Fortunately the shaft was repairable but at a substantial cost. For punishment, i.e. learning experience, I was given the task of measuring every manufactured part and comparing it to the drawing before it went out the door. Did this for about a month. Not to mention the ribbing I had to take from the other machinists. Taught me to be aware of where I'm at in the machining process before I reach "The Point of No Return". I still make mistakes and when I do I think of that boat shaft.

Tom S
 
That's a hard one to call, I have more scrap than I'd like just waiting some day to be made into something smaller, one memorable mistake was drilling and reaming two 1/2 inch holes for dowel pins in an assembled die set and not bolting it down, thinking it's 50 or 60 pound weight would be enough, I knew better, first hole went fine on the second hole I was to aggressive with the reamer and it fetched up, the die set started spinning on the table, before I had time to think centrifugal force took over and flung the die set right off the table, it could have hit me or the column of the drill press or someone else, it landed perfectly flat on the cement floor slid a few feet and done, not one bit of damage except some scratches on the bottom, the reamer looked like a hockey stick and my boss wasn't very happy.
 
My wife makes jewelry. She needed to mill out some square cavities in some ear rings. I got her set up on the Bridgeport type milling machine,but made the mistake of showing her how the rapid feed on the power feed worked. She,of course,forgot to raise the spindle before rapid feeding the table. Struck the 6" Kurt vise BOLTED DOWN TIGHTLY with the spindle, mover it 1/8"!!! Somehow she did not bend the spindle at all.

I tell you,machines and she do not mix. I don't let her use my HLVH.
 
Well I don't take full credit for this because in my mind a drill press is an evil thing. We had one in the shop I apprenticed in that had I think about a 50 horse motor on it and the work table was about 3" square, way to small to clamp anything down. Now I am going by memory here and I may be a bit off on my numbers. Flung a 1" thick 8" x 8" plate across the room. It also had a "drill press vice" that was 100% self propelled. It used to dart across the room like a cat with it's tail on fire.
One of the best stunts I saw though was not me but another apprentice. He had 1/4" x 1/2" piece of stock on a surface grinder. An wouldn't you know it, he forgot to turn the chuck on. Spit that thing out an shot it through a shop window, It made a perfect rectangular hole through the glass. We left it like that until he went to bigger and better things, or more likely busting bigger windows.

John
 
You must log in or register to reply here.
Back
Top