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The Most Damage I've Ever Caused In A Machine Shop.
- Thread starter Whyemier
- Start date
- Joined
- Oct 20, 2014
- Messages
- 495
Worst two things I ever did were in my home shop.
One instance was when I mistakenly added a chunk of scrap magnesium to my aluminum scrap bucket. It was late, I wanted to get through the rest of the 30 lbs of scrap to sort. Usually I file a spot, and drop vinegar on it. If it fizzles and blackens, it's magnesium. Goes to the recycler. This chunk I hefted, said "Ally", and chucked it in the aluminum bin.
Fast forward two months. I was casting ingots, and as I grabbed that chunk, I said, "Gee, feels a little light. Ahwell, it's in the ally bin, and I *ALWAYS* check."
Tossed it into the crucible. The smoke was the first indication of "whoops", followed by copious light, god-awful noises, and molten ally spattering everywhere. Only about 8 lbs in the pot when it all started. Threw about 80 lbs of sand on it, then changed my shorts. Was still hot 5 hours later, warm the next day. Ended up with 2 lbs of ally in a half-melted crucible, and a good 10 lbs of glass.
Next item was my induction heater/furnace. Home built, from scratch, myself. It ran on 240v, and had a 340-ish volt DC bus to feed the inverter. About 20 400v 3000uf caps in series/parallel for an 800v 30,000 DC filter cap. Bloody lethal beast of a DC supply.
The tank capacitor was a 5uf 1600v home-made unit that could laugh at 300A rms at 30khz.
It utilized a PLL to track the resonant frequency, and switched the inverter at zero current to cut the switching losses down. The inverter was an H bridge of 600v 70A IGBTs, four in each corner of the H bridge for 12 total. It would run happily at 8-10kw input, and could melt steel.
And Murphy decided he didn't like it. The all-important feedback lead that controlled the operating frequency went open circuit. The short bit of it left locked onto the strong 2mhz signal from a nearby radio tower. It tried to run the IGBTs at 2mhz, when their max frequency is only 100khz.
This turned on all 12 devices at once, effectively crowbarring that beastly DC supply with a dead short, plus the 240v mains for the instant it took the breaker to trip.
I thought a grenade went off. The cover of the induction heater ended up in the back yard, about 40' away. A 2lb heatsink wound up one street over. Several components were never found. They either got launched into orbit, or vaporized. I got off lucky with only a scratch from something.
The second time in my adult life I peed my pants a little out of fear. Then there was the dealing with the emergency services. No harm, no foul, but I'll never build another one, no matter how cool they are.
One instance was when I mistakenly added a chunk of scrap magnesium to my aluminum scrap bucket. It was late, I wanted to get through the rest of the 30 lbs of scrap to sort. Usually I file a spot, and drop vinegar on it. If it fizzles and blackens, it's magnesium. Goes to the recycler. This chunk I hefted, said "Ally", and chucked it in the aluminum bin.
Fast forward two months. I was casting ingots, and as I grabbed that chunk, I said, "Gee, feels a little light. Ahwell, it's in the ally bin, and I *ALWAYS* check."
Tossed it into the crucible. The smoke was the first indication of "whoops", followed by copious light, god-awful noises, and molten ally spattering everywhere. Only about 8 lbs in the pot when it all started. Threw about 80 lbs of sand on it, then changed my shorts. Was still hot 5 hours later, warm the next day. Ended up with 2 lbs of ally in a half-melted crucible, and a good 10 lbs of glass.
Next item was my induction heater/furnace. Home built, from scratch, myself. It ran on 240v, and had a 340-ish volt DC bus to feed the inverter. About 20 400v 3000uf caps in series/parallel for an 800v 30,000 DC filter cap. Bloody lethal beast of a DC supply.
The tank capacitor was a 5uf 1600v home-made unit that could laugh at 300A rms at 30khz.
It utilized a PLL to track the resonant frequency, and switched the inverter at zero current to cut the switching losses down. The inverter was an H bridge of 600v 70A IGBTs, four in each corner of the H bridge for 12 total. It would run happily at 8-10kw input, and could melt steel.
And Murphy decided he didn't like it. The all-important feedback lead that controlled the operating frequency went open circuit. The short bit of it left locked onto the strong 2mhz signal from a nearby radio tower. It tried to run the IGBTs at 2mhz, when their max frequency is only 100khz.
This turned on all 12 devices at once, effectively crowbarring that beastly DC supply with a dead short, plus the 240v mains for the instant it took the breaker to trip.
I thought a grenade went off. The cover of the induction heater ended up in the back yard, about 40' away. A 2lb heatsink wound up one street over. Several components were never found. They either got launched into orbit, or vaporized. I got off lucky with only a scratch from something.
The second time in my adult life I peed my pants a little out of fear. Then there was the dealing with the emergency services. No harm, no foul, but I'll never build another one, no matter how cool they are.
Last edited:
- Joined
- Apr 28, 2014
- Messages
- 3,590
Turning 30" stock, that lathe should have been bolted to the floor correctly. That's a lot of mass to be spinning and the lathe itself isn't going to have
enough mass to counter-act that.
The fault lays with the person or persons who didn't install it properly.
When I was in Facilities Maintenance, the mechanics would go over the machinery on a rotating schedule to verify that all was well.
On the large engine lathes we would turn 48" diameter cable spools and on others cable sheaves. Lots of heavy items.