The thickest, densest part.

with a plasma cutter it wont matter. you can cut a car in half in about 15 minutes with one.
cut the farthest place from the frame, to avoid the chance of damage.

BUHWAHHHH!!!! Not with Krypto keys man.

I would attack the shackle. As far from the bike frame as I could, on an angle that won't send the shower sparks directly onto the bike. I would also wear eye protection, and not hold my face in line with the wheel. I would figure out a way to hold the lock securely so that I could have both hands on the grinder. If the shower of sparks lands on your clothes it will eventually burn a hole in them. Don't worry, you'll know it when that happens.

Shackle? Whats that?
What i meant was, one side of this lock has a bent foot, and the other doesn't. I can't remember which side it was on, been over a month since i opened the lock. Cutting the side with the bent foot would probably make it a lot easier to open up, and only have to do one cut. That is, should i cut @ 1, or 2?

the bent foot is opposite the lock end of the U lock.
The lock end has the arow head tail that the lock clicks around when it's secured.

If you cut at the apex of the "u" farthest from the straight shaft, with the plasma torch, the lock should fall off when it's severed.

What I meant by the shackle is the "U" part. I would try to cut it so that I only had to make 1 cut. Lowers the chances of me messing something up that way.

Oh yeah, it may go without saying, but metal gets pretty flippin' hot very quickly when a grinder is taken to it. Ask me how I know that.

Insert appropriate disclaimer about the hazards of power tools here.

I've not ever cut a lock specifically, but I have cut all kinds of other metal with a plain $50 4.5" angle grinder and thin cutoff wheels. There's thin cutoff wheels that are only 1/8" or .015 or something like that, not the quarter-inch-thick ones. You might grab a couple, as they only cost a couple dollars each.

You will need a pair of vise grips to hold the lock with while you are cutting it, because where you're cutting the lock will get hot enough to burn the plastic covering off.

A torch or plasma cutter will certainly work, but these involve a lot more heat than a grinder does.
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yes but you're talking built up heat for half an hour on an angle grinder, vs extreme heat for a few seconds with the torch.
Either way you want to wrap the frame to protect the paint though, regardless of method.

If you go with the angle grinder it should take under a minute, even the stronger ones won't take more than a minute or two. Just put a wet non-synthetic blanket around the frame, or a fire blanket, either one will provide adequate protection for the time it'll take you to defeat the lock with a power tool.

I doubt it would take a half an hour. Looking at my own New York lock, I'd be willing to bet that it would take less than 60 seconds.

Also I can tell you that it'll get too hot to touch either way, but a cutoff wheel puts MUCH less heat into the part than a torch will. If you cut up thin sheet metal for instance, a welding torch will blaze right through it, but also the torch heat will warp the sheet badly. A cutoff wheel will slice right through the sheet metal but not warp it up from heat at all.
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Well...?

...coming soon from a holding cell in....

Aaron

I've helped a crew of guys cut through about 200 tons of metal with an angle grinder and a torch in the past 2 weeks. I envy the simplicity of this problem.

Thanks for your help guys. my friend ended up loaning me an angle grinder. it didn't have a guard on it though, so was pretty unsafe to use. but regardless, it took about 25 seconds to cut through the lock. it didn't really get that hot at all. and fell apart easily.

+1

Let's hear it for Power Tools! I trust you wore eye protection and gloves, etc. No, don't answer that.