Angle grinder question (yes, really!)

[Chris Hogg]

I want to cut some steel reinforcing bars for a neighbour, that stick up through the edge of their patio. I have diamond and bonded grit disks for the AG, but which should I use? I ask, because a car mechanic used the diamond disk for cutting through a broken coiled suspension spring on my car before taking the car away for repair. But I presume that spring would be hardened and tempered steel rather than these reinforcing bars which I imagine are simply mild steel and fairly 'soft', as they have been bent over.

[John Rumm]

The general rule is traditional abrasive discs for metal, and diamond for masonry.

However you can now get diamond discs designed for metal... but these normally say so in the description. e.g:

(and as for the demo video, if you need a lesson in how to knacker a disc, that should do it!)

In your situation, a depressed centre abrasive cut-off disc would probably be a good choice, since it can cut flush to a surface.

[newshound]

I think either would work. If you are going to be touching the concrete I might be inclined to use bonded disks to protect the more expensive diamond one.

Without looking it up, I think rebar is low carbon rather than mild steel, so a bit stronger than mild steel. But it will certainly cut OK with an abrasive disk, it is nothing like the hardness of a coil spring. (Which will also cut fine with an abrasive disk).

Changing the subject, I once had to get a large pipe hanger dismantled. This was assembled with a large preload, the spring was about three feet long, one foot diameter, one inch "wire", but compressed to 2 feet long. (They were built by winding it up on a long bolt, then the extended bit of thread was cut off).

I was quite worried about how the site services guys would do it safely. The answer was to attack it with a big gas axe; the process of cutting heated up a sufficient length so that all the strain was relaxed before the cut went through. I was very impressed.

[alan_m]

Just make sure that any sparks don't hit any upvc windows - protect with something that doesn't melt. Failure to do so may result in metal dust being firmly embed in melted plastic pits.

[tabbypurr]

Use grit. Diamond usually does poorly on steel, the metal dissolves the diamonds.

NT

[John Rumm]

That's what I just said.

Usually yes, unless you use one formulated for metal cutting as shown above - in which case they have a long life, but a slower cut rate than an abrasive disc.

[F Murtz]

Or glass,it will pit also.

[Chris Hogg]

Thanks for all the advice; I'll use a bonded abrasive disk, and make sure the fireworks are heading away from any windows.

[Brian Gaff (Sofa)]

It will make one heck of a racket though. Its ok for the person doing it having ear defenders, but what about the occupants and neighbours!

Brian

[Dave Plowman (News)]

I recently used mine in a jig for cutting square section steel tube. Got steel cutting discs for it. If you want a nice clean cut they need to be changed often. Not a problem if just hacking something off.

[John Rumm]

Every doubling in distance from the source will drop the sound pressure level at the observer by 6dB. So while they neighbours etc will hear it, they won't be injured by it.

(that and it takes all of 10 secs to chop through a bit of rebar)

[GB]

Do they burn, or do they get unbonded by the heat, ie the glue fails? Diamond burns in oxygen at around 1300 C, by the way.

Or the metal gets molten and the diamond really dissolves? Really?

[ARW]

I thought he was going to chop his balls off.

[tabbypurr]

Not something I have the expertise on. Sparks flying off the workpiece are metal that's red/yellow/white hot.

NT

[Fredxx]

Screwfix have some cheaper ones:

But I'm not sure if I like the idea of slots around the periphery.

I would expect this type of disk to be just as effective on masonry as a standard diamond disk.

[GB]

In a two minute video, he reduced that £20 disc from 115 mm to just the hub.

[John Rumm]

That was the abrasive disc he started with as a comparison - however all the twisting about with the grinder at the end of each cut is what destroyed most of that disc (in fact you can see much of it sprayed over the back of the steel!).

He followed it with multiple cuts using the expensive disc. Which needless to say did far more, and oddly he no longer seemed to be such a ham fisted muppet!

[Vir Campestris]

While I'll appreciate your practical experience tells us that it's a bad idea I doubt very much the diamonds dissolve in the metal.

Andy

[GB]

Thanks. I only watched the first couple of minutes, as that's my attention span. I thought that it wasn't a very good advert for an expensive disc! :)

[newshound]

Reminds me of once getting a very warm feeling in that region, after setting fire to a polyester boiler suit doing something quite similar to that (although a fixed object in a confined space, so I was more restricted in my positioning). Strictly cotton suits for "hot work" these days.