AR steel resistant to grinder attack? 3

[GrouseII]

Hi

I am creating an anti-theft automotive device which will be covered by a steel sliding box. Could someone advise me as to the best type of steel to specify that would be be most resistant to a cordless grinder/cutting disk attack.

I have looked at Abrasion resistant steel and case hardening but I am a lowly IT guy who has no such knowledge. I can go up to 3 or 4 mm thick and the box section is approx 20cm x 20cm x 30cm. Also what would be the implications of manufacturing. Can AR steel be easily worked/welded?

Hope its OK to pop up on this forum if not a professional.

Thanks Grouse

 

[SwinnyGG]

Tons upon tons of heavy machine components are made from abrasion resistant steels every day. Yes, it can be fabricated.

Machining will be potentially a lot more expensive than lower performance materials would be.

You should also know going in (if you don't already) that building anything our of steel with the intent of protecting from a grinder is a losing game. Nothing will ever be grinder proof- it's just a question of how long.

 

[racookpe1978]

I use a modestly thin mild steel case for the inside liner of the gun cabinets I've built, then place a fire-resistant/cut-resistant synthetic cloth wrap (Refrasil cloth is one common trade name) around that interior, then enclose both in an outside then metal (mild steel). Intent is to trap the drill or grinder wheel with the fibres and cloth to slow entry by the theif. And to help insulate the interior from a common short-term house fire. Get too, you'll lose the contents. But a simple torch or drill or bandsaw can't get through without extreme effort.

For your case, think of a Kevlar wrap - you're looking for cut resistance, not fire-proofing. A hand-held battery-operated Dremel-type tool can't make a long cut through any of the heavier gauges. A six-inch Metabo commercial grinder running an 0.045 thick cutting wheel?

 

[berkshire]

I do not know how complicated you want to make this box, but one thing that defeats grinders is a rotating bar. A freely rotating spindle will eat up a grinding wheel. Look at a grinding wheel dressing tool to see what I mean.
B.E.

You are judged not by what you know, but by what you can do.

 

[GrouseII]

Many thanks for such insightful responses.

1. The rotating spindle idea could easily be incorporated into my design to protect one of the most vulnerable parts. Is it the concept that the grinding wheel cannot get any purchase on it or does it need to have the spinning dressing wheels as part of it to wear down the disk?

2. Sandwiching is not something I had thought of but sounds effective. I assume the idea is to have long stranded fibres that wrap up into the grinding spindle to choke it. Kavala appears to be £100 per sqm so would over price the device I think.
Is there an industry method of manufacturing sandwich plate steel or is it literally get a fabricator to weld up each panel of my device manually inserting the fibre/cloth?

Really impressed with this forum that you guys are happy to share your knowledge with a non techy

Thanks again

Grouse

 

[berkshire]

The concept is that the grinding wheel cannot get a purchase on the part, but will still lose pieces of the grinding wheel. It works against saw blades too.
B.E.

You are judged not by what you know, but by what you can do.

 

[DrewMoto]

I agree with the other posts here and love the out-of-the-box suggestions. I have a lot of experience fabricating steel and aluminum parts by hand. Another way I can think of to significantly slow down cutting progress is to cause binding. This works with grinding wheels and saws. Once the cutting implement gets far enough into the workpiece that the piece can bend so as to decrease the kerf width, the faces of the cut grip the wheel or blade very effectively. It usually results in stalling the electric motor or kicking the whole tool out of the cut, and seriously shortens the life of the wheel or blade in the process. I don't know what your design looks like but you mentioned there is a particularly vulnerable point that would likely be attacked first. If you could assemble your device so that the vulnerable part supports a bending moment, such that there is residual compressive stress in the material that faces outward, it would be a huge PITA to cut through. To see this for yourself, support a 2x4 on its ends using saw horses, then try to saw through the middle.

 

[racookpe1978]

It would take more space (more volume) and add weight, but you could make an lightweight (thin metal) enclosure for the gadget.
Make a second, outer enclosure 3/8 inch larger on each side that is thicker. Made of more expensive steel if you wish.
Pack the space between the two with loose ball bearings whose diameter is larger than the thickness of the biggest grinding wheel you need to protect against. 1/4 inch wheel is about the thickest I've ever found commercially.

Thief tries to start grinding, gets through the outer enclosure. Ball bearings roll when hit, don't let the wheel get a grip. The bearings are too big to roll out of the groove cut.

 

[DAVIDSTECKER]

I would think that the flaming car inter started by the grinder sparks would keep a thief from obtaining their goal.

 

[ornerynorsk]

Strategically placed tungsten carbide rods will slow down the would-be thief.

Also, along the lines of the layering/sandwich idea. Some thick natural rubber or other elastomeric product sandwiched into the steel would not only gum up the grinding disc, but it's going to stink and smoke terribly.

Nothing will 100% deter an assertive thief, it's the time factor. Thieves don't want to hang around too long, as the odds for getting caught go against them the longer it takes to crack the target.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[IRstuff]

Don't forget that whatever you are attaching this theft-proof device is not theft-proof, so as with ye-olde steering wheel locks that used to be very popular, the steering wheel itself is made of less sterner stuff.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[berkshire]

I am reminded of a story from my apprentice days. we came into work one morning to find the door open ( Not a good sign.) and the building reeking of smoke.
During the night, thieves had bypassed the alarm, they had opened the front office and carted the office safe onto the workshop floor. They had then used an Oxy Acetylene cutting torch to cut the back off the safe. They had removed about Ten pounds worth of petty cash and absconded.
Upon inspecting the safe I noted that the door and sides of the safe were massive, about 3" thick multi layered. The back where the thieves cut through was only one layer of 3/16" thick steel. The police said that they doubted that it took the thieves more than ten minutes to cut that safe open.
It was supposed to have been buried in a wall which it was not.
B.E.

You are judged not by what you know, but by what you can do.

 

[GrouseII]

Thanks for the extra input. Certainly food for thought.

The bendy idea where I assume the idea is to pinch the grinding wheel sounds very cool but alas doesn't suit my design.

Fortunately I have factored in the issue that a would be thief could just cut part of the car so hopefully that's dealt with.

hmmm ... ball bearings could be introduced, i have the space but I am thinking the rubber idea has legs for me. The smoke and stickyness could well do the job.

Should have realised a forum full of engineers would go above and beyond with ideas when given a problem :'D

Grouse