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Inspired by this story about Paris authorities ordering removal of thousands of "love lock" padlocks from bridge railings. This is not a DIY SE question because it's not DIY scale in the first place.

So suppose we have several dozen meters of valuable metalworks (perhaps some one hundred years old forged or cast railings) and so we cannot just melt the whole thing and produce new railings. We have to remove the padlocks and place the railings back. And we'd be happy to do all of that over a week or so, not waste a year.

Let's assume that we're not required to work on the bridge and can remove the railings for a while (and install cheap looking temporary railings for that period).

What would be an adequate technological process for that? Cutting with boltcutters? Cutting with angle grinder? Cutting with gas welder? Anything else?

locks on railing

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    $\begingroup$ 5 people with bolt-cutters x 2 padlocks per minute = several thousand padlocks removed in a day $\endgroup$ – 410 gone Jun 2 '15 at 13:58
  • $\begingroup$ @EnergyNumbers Good, except I have no idea how many cuts on hardened locks a real bolt-cutter can do before it gets dull and useless. $\endgroup$ – sharptooth Jun 2 '15 at 14:01
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    $\begingroup$ I rather suspect that almost all of the padlocks will be cheap & unhardened $\endgroup$ – 410 gone Jun 2 '15 at 14:19
  • $\begingroup$ I haven't seen noise yet as a consideration on any of these answers/comments. I would imagine a tourist destination would not want a lot of angle grinders running at any time. I would vote for a lock picking sweep first to remove the majority of the locks and then cut the difficult (with oxidized pins) locks off during a non-peak tourism time. $\endgroup$ – morristtu Dec 4 '15 at 12:38
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Just do it

Since the primary requirement is to not harm the existing structure, anything that is done will have to be manual. Humans are good about dealing with varying conditions. Each lock type, shape, and location is different.

We don't trust robots to excavate archeological sites for the same reason.

Do no harm

Even with humans manually cutting the locks, the method used needs to be easy enough to control and contain so that the structure isn't damaged.

  • Grinders have blades that are relatively large and will need to be used in a confined space. There is a danger of accidentally cutting the structure.
  • Plasma cutters have a real risk of over cutting through the lock and damaging the structure.
  • Gas cutting torches have the same drawbacks as plasma cutters.
  • Mechanical bolt cutters can be positioned accurately, and it is easy to see exactly what will be cut. They can be hydraulically powered to lessen the physical exertion.

It would be relatively quick and safe to cut the locks manually. If any individual lock is difficult, it can be skipped. These few locks can be dealt with later once there is more space. This will keep the production level up.

A different solution?

The question (and my answer to this point) has focused on cutting the lock off. These are likely cheap and common locks that would be easy for a locksmith to remove.

An experienced locksmith with the right tools (bump key, vibrating gun thing, etc.) may be able to walk down the line actually unlocking the locks. This would be by far the easiest route and it might even be quicker. Even if it only worked for a subset of the locks, it would be something easy to try.

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The portable angle grinder that I saw them using on TV looked very effective.
In the hands of a competent workman the risk of damage is minimal. With a cutting blade this is more a "geared metal saw" than a grinder per se.

Blade size could be selected to be only as large as needed for most locks.
Use of a diamond cutting blade that was as durable as possible would minimise the need for blade changes.

While I suspect that the tool they were using was liable to be as good as most, another one which is very uncommon in this sort of application suggests itself.

A carborundum grit or sapphire or other media air powered cutter could be as capable as desired. These are used in industrial cutting applications for metal up to many times the thickness of the largest padlock.

While this would require a significant air supply, a portable compressor of any desired size could be provided. This may be more expensive to setup than most other options but would provide close to "hot knife through butter" cutting and precision cutting location once established.

  • A guide could be provided to fit through a padlock hasp so no cutting would happen for any grit that got past the 'target',

  • A recovery tube with suction could be arranged to recover most of the cutting agent and

  • A hood that swung over the cutting area to minimise back spray.

All this would take some design and setup - but not excessive compared to the task and, once running it would be very fast.


Note - bolt cutters: Many locks, even quite cheap ones, are hardened. A suitably huge bolt cutter will tackle many hardened locks but the weight and jaw size gets very very large and it would be very impractical for the number of locks involved. - I heard an estimate of 45 tons on the initial bridge alone.

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cutting with oxygen torches or angle grinder will likely cause damage to the railings. Heat damage from the torch and abrasion damage from the grinder spray.

For any of the non boron carbide/standard metal shackles, some type of powered bolt cutters could be used.

The locks with the super hard shackles like boron carbide, chill it with liquid nitrogen and shatter the shackle with pneumatic air hammers/chisels.

Anything else can be plasma cut.

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A handheld battery, pneumatic, or hydraulic would be the best bet. There is very little risk of damage to the railing as compared to some of the other suggested methods and while you lose some time when compared to a grinder or torch, the accuracy outweighs it, given the value of the railings. This would also eliminate the need to remove the railing from the site and eliminates the need for human strength (cutting a few thousand bolts would get tiring).

One suggested option is a battery powered handheld rebar cutter: https://www.genscoequip.com/admin/products/attachments/NEWBC16Boltcutter.pdf

Multiple batteries would be required though and you would likely need 3-4 people, each with their own.

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Hydraulic spreader, as used in rescue operations, will make a short story of all the tougher shackles without damaging the structure or itself - specifically applied not to "straighten the 'U'" of the shackle, but to pull the shackle out of the lock body - the latching mechanism is usually much weaker than the shackle itself, and even if it isn't, you're acting against the weakest part of the shackle (notch allowing latching) instead of the sturdy lock body. You might contact the local rescue / fire brigade and ask if they wouldn't help. They might tackle the task as an opportunity to train precise use of the equipment.

enter image description here

The smaller, more "lightweight" padlock will be faster dealt with using standard bolt cutters.

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bolt cutters are the normal tool used by self store places and such to remove locks.

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    $\begingroup$ This answer is a bit thin. It might be helpful if it were expanded upon. $\endgroup$ – wwarriner Dec 2 '15 at 0:59
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    $\begingroup$ A self-store place doesn't have to remove thousands of locks at a time. $\endgroup$ – hazzey Dec 2 '15 at 3:16

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