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I have a bicycle that's locked with a 2 cm/0.8" hardened steel lock that I have unfortunately lost the key to. I would very much like to get the bike operational again, but all I have is a 900W reciprocating saw. I had some moderate success with it and a metal blade, until the blade became dull after getting about 1 mm through the lock. Note that this was a very cheap blade, and I'm sure I can get some that are harder and more durable, but is it actually worth the effort and cost of blades to use a reciprocating saw for this? Or is an angle grinder a better tool that I should acquire instead?

EDIT: And for those who are curious, the lock looks like this: The lock.

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    What kind of lock, pictures, model #? Many bike locks are easy to undo without the key. – Sam Jan 3 at 17:02
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    Can you post a pic of the lock on the bike? It may be possible to remove the lock by disassembling some part of the bike (assuming its not through the diamond frame somewhere) This also assumes you are the legal owner of the bike. – Criggie Jan 4 at 1:51
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    For such a thickness, i would do that with a big angle grinder, Plasma cutter or Oxygen cutter. But these are tools not everyone possess, and require a certain amount of experience to be used. In the present case, i'd try, as @JPhi1618 says below, to search for how to lockpick that. – Benj Jan 4 at 12:38
  • Absolutely do this from the non-drive side (the left side of the bike) and use some protection like a welding blanket, or scrap wood, or similar to protect your bike from the heated dust. I'd even tie the bike to something immovable like a fence post while grinding on it, and even hook a weight onto the lock to restrain it from moving. You'll need two hands on your grinder. – Criggie Jan 4 at 21:49
  • The chain in those handcuffs is high-tensile steel. It'd take you ten minutes to hack through it with this. Now, if you're lucky, you could hack through your ankle in five minutes. Go. – Mazura Jan 5 at 2:31
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For cutting locks, nothing beats an angle grinder. Good locks are all made with hardened steel that should be as hard as any metal cutting blade for a saw. The reciprocating saw will be able to make a little progress into the shackle, but its speed will dull the blade quickly, and once it's even a little dull, it will stop cutting and melt/grind the teeth completely off.

A grinder on the other hand works by heating the metal, softening it and scraping away particles. The grinding disk is meant to be consumable, so rather than getting dull, it just wears away as it does the job.

Of course, you should also consider that a lot of locks are very easy to pick open. While you are trying to get access to a grinder, spend a few minutes to research picking and determine the type of lock you have. It's unfortunate, but many locks claiming to be "high security" can be picked in minutes or seconds using improvised tools.

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    Angle grinder disks come in different thicknesses. Thicker ones are for grinding on the flat and edge of the disk; thinner ones are more appropriate as a 'cut-off' tool for edge-on grinding. – user109695 Jan 3 at 16:36
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    @Jeeped I should have mentioned that - yes a thin "cut off wheel" would be best for this. You can grind through a lock with a thick grinding wheel, but it takes much longer and throws off a lot more material. Also when using a cut off disc, go slow in the beginning. It's not a race, and focus on keeping the tool straight and steady. Going too fast is an easy way to jerk the tool out of your grip and/or break a disc. – JPhi1618 Jan 3 at 16:41
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    When I had to cut a lock off my bike, I used a Dremel cutoff disk -- took a lot longer than a real angle grinder would have taken, but it's all I had on-hand and it worked. – Johnny Jan 3 at 17:38
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    @Johnny Yeah, that's my go-to. It's amazing what I've cut with those. – Harper - Reinstate Monica Jan 3 at 19:02
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    When doing this, be mindful of where the hot spray of sparks and hot metal goes. You don't want it blasting on your bike, or anything else you care about. – Criggie Jan 4 at 1:50
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Although an angle grinder with a thin cut-off (type 1) wheel is the right tool; if you don't already have one then you can pay well over $70 for a good one.

You should look into diamond-grit or carbide-tipped blades per https://www.discountsawblade.com/Articles.asp?ID=264

If you dull down a section of the blade then you should be able to carefully continue cutting with a different section of blade since the reciprocating action only involves about 2 inches of movement and you have a 9 inch blade's worth of cutting material.

Additionally, if your reciprocating saw has an "Orbital" setting then make sure it is turned off or else your saw will be uncontrollable. Orbital is immensely useful for cutting wood though.

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    Even a cheap grinder (less than $25) would do this job. Sure, it's worth investing in a quality tool if it will be added to the tool box for future jobs. For a one-off, a Harbor Freight or Amazon.com cheapie would be more than sufficient. – spuck Jan 3 at 16:38
  • @spuck That's for OP to decide. I would certainly add a quality angle grinder to my arsenal if the need arose but buying one (even cheaply) just to handle a single lock would not be my first thought. I would get more future use out of a quality blade to compliment my reciprocating saw. – MonkeyZeus Jan 3 at 16:40
  • Depending on how hard the lock is, you're looking at quite a few saw blades to cut through it. One of the many things that came through the mechanical-testing lab I once worked at was a set of bicycle locks; the testing spec called for wearing out 200 hacksaw blades without making a cut more than 2 mm deep. – Mark Jan 4 at 3:02
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    4-1/2" grinders are all extremely cheap even from the most reputable companies (because they are mostly useless but would be fine for a job like this). However even a hazard fraught grinder will usually last for years and is more than adequate for a home gamer. – jesse_b Jan 4 at 15:36
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    @Mark You are speaking of ordinary carbon- or high-speed steel blades. With the correct diamond or carbide saw blade (as he is specifying in this answer), it should be able to cut through several of these locks before needing replacement. – Mike Waters Jan 4 at 21:58
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We used to call this a 'hot wrench'.

enter image description here
Cutting or Blow torch

Most any automotive repair, metal working shop or even a decent bike repair shop will have one and they shouldn't charge that much to blow the old lock off the bike.

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    I couldn't help but imagine that the shop might ask "Where'd you get this bike from?" – MonkeyZeus Jan 3 at 16:47
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    True dat but it doesn't really matter if proceeding with a clean conscience. An angle grinder is the best route and any home handyman should have one anyways but I haven't used the term 'hot wrench' for quite a while and this was a good opportunity. – user109695 Jan 3 at 16:48
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    @Jeeped that’s a Louisiana spanner... – Solar Mike Jan 3 at 19:06
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    This is the answer to title of how to cut inch-thick steel (plate), +1. – Mazura Jan 5 at 2:28
  • @Jeeped While cutting torches are great tools for some things, I'd not use one in this case. It will splash burning iron all over the bike. An angle grinder is easier to control, and the material to be removed small enough that it doesn't really matter. – vidarlo Jan 5 at 9:29
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Get a torch and heat up a section until it turns cherry red and then allow it to cool. This will cause it to lose its temper and it will be soft enough to cut. You can then cut it with a reciprocating saw, angle grinder, or bolt cutters. If you use heat, protect the frame of the bike by wrapping it with a damp towel. You could also try finding a locksmith to pick the lock.

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