On Tuesday, December 5, 2017 at 2:01:04 PM UTC-5, Jeff Liebermann wrote:
On Tue, 5 Dec 2017 10:15:54 -0800 (PST), Frank Krygowski
wrote:

I've wondered about a sort of multi-layer lock. Start with a strong cable,
say about 3/8" diameter. Have it threaded through a hardened steel tube with
thick walls. Have that tube encased in steel rings - say, cylinders whose OD
is just a bit larger than the ID of the tube.

My hope would be that the rings would spin so a grinder would be inhibited.
The tube would crush under bolt cutters and protect the cable.

I haven't given any thought to bending around corners or a lock mechanism.

Sigh. All you're doing is applying familiar metallurgical solutions
to the design. The problem is that they are all limited by the
limitations of the materials. The closest approximation to cut proof
are the various titanium locks:
https://www.tigrlock.com
https://altorlocks.com
It's possible to grind titanium (about the same as stainless steel).
The main limitation of a metallurgical solution is that anything that
can be fabricated can also be cut. Even the highest temperature
alloys can be cut by an even higher temperature torch, such as a
mythical portable plasma cutter. If overheating is impractical,
freezing with liquid nitrogen can make it brittle enough to break.
Like an arms race, the results are predictable and the effort usually
futile. The best you can do with metallurgy is to make the lock too
expensive to cut.

Perhaps a different approach might work better. The problem faced by
the average criminal is to steal the bicycle without destroying it.
That's easy when the lock is an independently removable accessory.
However, suppose the lock were designed and built as an integral part
of the bicycle frame. Cutting the lock would destroy the value of the
bicycle making the theft much less profitable.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Then the thief chops the frame and sells just the components. Many thieves discard the frames anyway as they are easier to track/identify than are the components on the frame.

Cheers