crackerdog

Anyone know of a material that can't be easily cut with an angle grinder? I have an idea for a lockable parking space for bicycles but if anything can be cut with an angle grinder in 30 seconds, it won't work, in fact, if that is the case we can never have safe outside parking. Any ideas?

Jamesw2

Diamond . . See what they put safes together with . . my understanding the more layers the more difficult it it to cut drill or saw . . some bank vault company's put carbide chips along with stainless steel turnings in the floor and walls . .

https://www.amazon.com/Abus-Locks-495...r_194614011_57

https://www.amazon.com/Lock-Alarm-8-f...4743960&sr=1-2

Myosmith

The problem with most materials that can't be cut relatively easily with an angle grinder and the proper disk/blade is that it is going to be a) very expensive, b) very brittle and hard to work with, and/or c) extremely heavy. As mentioned by James, something like a high carbon, high molybdenum steel, such as VG-1 or ATS-34, hardened to a Rockwell B-scale of >60 would be hard to cut with an angle grinder. Adding carbide bits would further wear on the blade, slowing progress. The problem would be brittleness so you would have to use a fairly thick cross section and design it in such a way that it would be difficult to strike forcefully at an angle or to pry sideways to failure with a jack. Steel like this isn't cheap and is harder to work with than many other steels. They would be saw and grinder resistant but vulnerable to cutting torch or impact/lateral force. Clever design might make it more difficult by making it difficult to get a good angle and purchase on the material to complicate the logistics of cutting through it.

Making a practical cable or chain that can't be cut with a diamond wheel on an angle grinder is a tall order. The paradox is that in order to work with a material, someone has to come up with a way to cut and machine it, ergo the same means used to produce it can be used to defeat it.

I'm not sure what you are looking for in your design, but if you are looking for something to lock the bike to, a heavy walled, hardened steel pipe filled with a ceramic with a carbide filler would be slow to cut and more practical than a custom steel with embedded carbide. You still have the problem of what to use to lock the bike to the stable object.

There is and never will be such a thing as "theft proof". The best you can hope for is to make your bike a PITA for the thief to steal so they will move on to an easier mark.

ftwelder

I think much of what you are looking for will come with a decent design. many security items are made of tubing with a piece of bar stock built inside. When the grinder wheel hits the bar, the bar spins preventing further cutting. Fabrics like those that chain saw chaps are made out of are designed to tangle in a blade stopping the saw. Fill hollow parts with die that stains or something that burns the eyes like mace when the item is tampered with like "tilt" in an old pinball machine.

"edge" or hard-facing, a WRP (wear resistant plate) would certainly delay the process.

BR46

The harder it is to cut with a grinder the harder it will be to machine into the shape. I think if a thief wants it there going to get it all you can do is slow them up.

Looigi

IME, Ti is relatively difficult to cut with an abrasive cut-off wheel. Hardened tool steel like drill bits or hardened lock shackles are relatively easy and fast to cut. Soft materials like aluminum or copper load up the wheel.

kenji666

Unobtainium is pretty hard

StephenH

My idea is to use metal or PVC pipe of a fairly large diameter, fill it was steel cables, marbles, and tar. The large diameter prevents bolt-cutters from being used, and hopefully the fillers would make it difficult to use saw blades or angle grinders. I haven't yet experimented with this idea, though.

xenologer

How about water?
It's near impossible to cut, it reseals itself as soon as the blade passes through.
Athough a lock made of water will be vulnerable to the freezing-it-solid-then-tap-with-hammer trick.

Still, the self healing property might be a good direction to explore.
There are other materials that are also self-healing; rottweiler's for example.
Yeah, a lock made of rottweiler's might be just the ticket.

genec

isn't there already a lock made of Ti...

https://tigrlock.com/

kenji666

Why an angle grinder? What kind of cutting wheel? Why not a cutting torch? What happens if it takes 45 seconds to cut through it?

Drakonchik

Like that tigrlock.

crackerdog

No, I was thinking of a locking system that would be installed by the city in certain heavily used areas. No need to install your own lock so weight wouldn't matter. If we are going to get people to commute more, we need a safe locking system for bikes or some way to stop thieves from stealing them. I have a real beater that I use if I want to go to the theater at night. Only $40 bucks into it so if someone steals it, I won't feel like killing the thief, just breaking their legs.
You've given me some good ideas, I'll work on a design.

xenologer

A city provided locking system for heavily used areas?
Well that's easy then, a bike locker.
With a credit card reader that both serves as payment as well as the key (must bring back same card to unlock later, and it charges by the hour).
Since its a pay system you an afford to make it secure; ie having a guard on duty.

genec

agreed... since cities already provide a wide variety of parking for motor vehicles, the city should not feel "put out" by also providing secure bike parking.

squirtdad

no matter what the lock is....if a thief want components..... you can get through most frames in seconds with a old fashioned hack saw.

PDX Reborn

My thoughts exactly. I imagine most, if not all bicycle frames can be cut thru, in a matter of seconds. Perhaps, a combination of hard steel and some sort of audible, theft deterrent device featured into the rack design, to give a potential thief more greif for his efforts. Say, if the bike is locked in and jumbled around, it would trigger a loud audible alert to draw attention to the thief.
Some floor heaters feature an audible alert, for tip overs.

crackerdog

Our tourist board (the historical society) won't let anything be installed downtown that doesn't look right (to them). They didn't like bike bars until it was made clear to them that bicycles were here before cars. Had to prove it with old newspaper accounts.
You are right about thieves cutting frames for the parts so I guess I'll just use the cheap bike at night.

asmac

Would there be any benefit to a metal tube filled with bearings that would simply spin when the grinder got to them and prevent it from cutting any further? How about an "active armour" system made of some material that would generate clouds of smoke when heated up by a grinder?