Locks that work

For anyone that's interested, we did some chain link cutting tests comparing a cordless grinder with a powerful mains grinder, in a vice and on the floor and also completely hand held. I said to Jonny69 that we don't want to reproduce actual time figures as that might show a thief that his "quick cutting time" could perhaps be quicker, but the ratios are perhaps more meaningful anyway as it gives some guidance on what might be gained by using a thicker chain and/or using it properly.

We did some cuts on our Protector 11mm, 13mm, 16mm and 19mm chains. These were held in a vice and cut with a Dewalt mains grinder and also with an 18v Dewalt cordless grinder (with fully charged lithium battery), and we also did some cuts with a chain lying on the floor and holding the chain by hand.

The ratios between similar cutting tests were as follows:

The cordless grinder typically took 2 to 3 times as long as the mains grinder to cut the same link, with the thicker chains being the 'worse' ones to cut in terms of ratio as well as timing (naturally). I think this is because the thicker chains bind more on the sides of the disc as the cut gets deeper, which obviously applies more in the thicker chains.

With a cordless grinder, the time taken to cut the 11mm vs. 13mm vs. 16mm vs. 19mm was around 100% : 200% : 280% : 367% as percentages of the time to cut the 11mm chain. E.g. it took twice as long to cut the 13mm compared with the 11mm.

Cutting a 13mm chain link lying on the floor with the cordless grinder took about twice as long as when it was held in the vice, significantly, cutting it when it was swinging around in mid-air and I was holding the link by hand, took about 5 times as long as when in a vice (or more than 3 times as long as when it was on the floor).

I think these last figures are the most important of all as they illustrate why we always say you should try to keep a chain off the floor. This makes it much harder to cut with a grinder and also with bolt croppers.

This suggests you might be better off using a 13mm chain 'properly' (particularly keeping it off the floor) rather than having a 16mm chain lying on the floor.

These poorly gripped situations (on the floor or in mid-air) are actually likely to be non-linear as I found the 13mm link was repeatedly snatching in the cut and in fact, so much so, that I would refuse to attempt even a single cut of a handheld 16mm link let alone 19mm! Even with a cordless tool, which is relatively weedy compared to a powerful mains grinder, it was decidedly dangerous on just a 13mm link and it is as you get deeper into the cut that it becomes more likely to snatch. Naturally, a 16mm or 19mm link requires a deeper cut, even with me rotating the link around in order to minimise that effect. It would be harder to rotate a larger link and in a real-life theft situation it would be happening at a mid-point in a run of chain rather than an isolated few links like I was doing. So, the manipulation time would increase significantly and the snatching risk would increase markedly, so you’d have to be very desperate to even try handheld cutting on thicker chains IMHO.

We didn’t try any scenarios where one person was holding the chain and another person was using the grinder. That would presuppose a situation where there is enough room to get 2 people close to part of the chain, which also hints at incorrect use of a chain, just as leaving a chain on the floor.

We also didn’t attempt anything in an awkward handheld position. The only handheld cut I did was scary enough as it was, honestly, when I could rest the link close to my leg.

So, the summary is that whatever you do, it is crucial to keep the chain off the floor (and similar findings would be expected with a D-lock etc).

I hope that helps.