Re: Angle grinder question (yes, really!)

[John Rumm]

On 04/07/2020 11:52, Chris Hogg wrote:
> 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.

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:

https://www.toolstation.com/mexcel-metal-cutting-diamond-blade/p31448

(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.

--
Cheers,

John.

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[newshound]

On 04/07/2020 11:52, Chris Hogg wrote:
> 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.
>

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]

On 04/07/2020 11:52, Chris Hogg wrote:
> 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.
>

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.

--
mailto : news {at} admac {dot} myzen {dot} co {dot} uk

[tabb...@gmail.com]

On Saturday, 4 July 2020 13:27:38 UTC+1, John Rumm wrote:
> On 04/07/2020 11:52, Chris Hogg wrote:

> > 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.
>
> 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:
>
> https://www.toolstation.com/mexcel-metal-cutting-diamond-blade/p31448
>
> (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.

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


NT

[John Rumm]

That's what I just said.

> Diamond usually does poorly on steel

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.

[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

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This newsgroup posting comes to you directly from...
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[Dave Plowman (News)]

In article <mqm0gfhi6i0auojt7...@4ax.com>,

Chris Hogg <m...@privacy.net> wrote:
> 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.

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.

--
*Why 'that tie suits you' but 'those shoes suit you'?*

Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.

[John Rumm]

On 05/07/2020 09:37, Brian Gaff (Sofa) wrote:

> 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!

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]

On 05/07/2020 01:54, tabb...@gmail.com wrote:

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

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]

On 04/07/2020 13:27, John Rumm wrote:
> On 04/07/2020 11:52, Chris Hogg wrote:

>
> https://www.toolstation.com/mexcel-metal-cutting-diamond-blade/p31448
>
> (and as for the demo video, if you need a lesson in how to knacker a
> disc, that should do it!)

I thought he was going to chop his balls off.

--
Adam

[tabb...@gmail.com]

On Sunday, 5 July 2020 13:55:26 UTC+1, GB wrote:

> On 05/07/2020 01:54, tabbypurr wrote:
>
> > Use grit. Diamond usually does poorly on steel, the metal dissolves the diamonds.
>
> 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?

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


NT

[Fredxx]

On 04/07/2020 13:27:36, John Rumm wrote:
> On 04/07/2020 11:52, Chris Hogg wrote:
>> 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.
>
> 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:
>
> https://www.toolstation.com/mexcel-metal-cutting-diamond-blade/p31448
>
> (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.

Screwfix have some cheaper ones:

https://www.screwfix.com/p/lenox-metal-diamond-cutting-disc-115-x-22-2mm/200hy

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]

On 05/07/2020 01:54, tabb...@gmail.com wrote:

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

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]

On 05/07/2020 20:00, John Rumm wrote:
> On 05/07/2020 15:33, GB wrote:
>> On 05/07/2020 14:02, ARW wrote:
>>> On 04/07/2020 13:27, John Rumm wrote:
>>>> On 04/07/2020 11:52, Chris Hogg wrote:
>>>
>>>>
>>>> https://www.toolstation.com/mexcel-metal-cutting-diamond-blade/p31448
>>>>
>>>> (and as for the demo video, if you need a lesson in how to knacker a
>>>> disc, that should do it!)
>>>
>>> I thought he was going to chop his balls off.
>>>
>>
>>
>> In a two minute video, he reduced that £20 disc from 115 mm to just
>> the hub.
>
> 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!
>

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]

On 05/07/2020 14:02, ARW wrote:

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.