An actual angle grinder question...

I'm using some Bosch 1mm thick cutting discs to chop up some 1" square steel tube - approx 1mm thick walls. Angle grinder mounted in a stand which sort of makes it a chop saw. The discs appear to go blunt quite quickly. Noticeably faster on the first use - and need changing after about 6 cuts, although not obviously worn. I thought these things had the abrasive all the way through? So would work pretty well the same until worn out?
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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That's how it ought to be. They should last for ages. Hundreds of cuts per disc usually. I can only think they're glazing up and the pores in the abrasive are filling with some sort of debris. Are the tubes clean metal or are you cutting through some sort of paint or powder coating as well? If so that'll likely be your problem. You can probably recondition the old discs by using them hard against some old clean scrap metal or even stone just to get back to clean edges.
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Black paint - I'd guess powder coated. It's Dexion SpeedFrame.

Thanks Dave - I'll try that. Unlike everyone else on here I hardly ever use an angle grinder since I'm terrified of the things. Only really used them on stone before.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 08/02/2014 19:00, Dave Plowman (News) wrote:

With me, it's a mixture of terror and revelling in the sheer power of the beasts, especially the big one.
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Easy enough to see if this is your problem. Just trying making a few cuts with a new disc in some old unpainted angle iron or whatever. If the performance stays as new with unpainted metal then Bob's your aunty's husband. Might be worth just scratching off the powder coating first with a hacksaw blade using a bit of wood or metal clamped to the Dexion to give you a straight edge to run against.
Also use a bit more pressure and cut through it faster if you're really not very used to the things and being unduly gentle. Abrasives actually need to break down in service to keep presenting new cutting edges to the workpiece and overly light usage is often worse for them than being a bit rough. The powder coating will be smearing into the structure of the disc and blocking it up if you don't belt through it quick and once any sort of abrasive is glazed the performance drops off like a stone. They can literally go from "knife through butter" to start with when everything's new to chattering and squealing and producing a finish like a ploughed field in moments once the pores block up.
In "proper" engineering like wot I do we're always fighting against abrasives whether in surface or cylindrical grinding or honing applications like for engine bore resizing. They're wonderful things if you can get the grit specification and bond type, speed, feed and pressure as well as the coolant and lubricant all specced right for the material being ground. They're little bar stewards if any of those is not quite right.
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On 08/02/2014 20:10, Dave Baker wrote:

Couldn't have put it better myself.
I assume you are wearing a face shield, or at least safety goggles. Given that your "stand" is hanging on to the tool and giving you a nice square cut compared to doing it by hand, you really can lean on them quite hard and even if the disk does do break, there is a lot of fibre reinforcement in them. They break up in a relatively benign way without chucking out large, fast moving chunks. The only real risk doing it by hand is that you lose control of the tool because of the kick and the vibration, and end up catching something with the remains of the disk before it stops.
Angle grinder disks are *very* different from grinding stones which, if they do fail, produce shrapnel like a hand grenade. This is why, in industry, only suitably trained persons are allowed to fit them.
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Abrasive disks do wear out pretty quickly. They cut slower as the diameter is reduced (hence the speed the cutting edge travels at.)
You can get tungsten tipped wheels/circular saws for metal cutting that last better. Expensive. I think they have them in screwfix.
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But they're not noticeably worn. If they were I'd not be able to cut through 25mm tube as they only start off at 115mm diameter - so not much spare before the gearbox hits the work.

I wondered about them - but it wasn't too clear if they were ok on steel.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Back when I was still in the engineering steelwork trade the cutting discs for a Bosch grinder were nominally 3mm thick and would keep going until there was almost nothing left of them. In other words , they reduced in diameter in relation to the amount of work they did.
On 08/02/2014 17:47, Dave Plowman (News) wrote:

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On 08/02/2014 17:47, Dave Plowman (News) wrote:

Chances are the disc is getting clogged or glazed... after one has dulled I would be tempted to use it to cut into a bit of brick to dress the edge again.
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Thanks for all the advice - the answer was not to be scared of it and use more pressure. I was 'letting the cutter do the work' - wrong in this case.
Next thing is the B&Q grinder I was using has clapped bearings. (It's not had much use) My other one is an ancient Wicks - but has a larger gearbox so won't cut all the way through. Might have to pop out tomorrow and get a new one from Toolstation etc. Any recommendation? With a low profile gearbox?
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On 09/02/2014 00:06, Dave Plowman (News) wrote:

My 9" Hitachi has spent its entire life cutting masonry of one sort or another - the bearings and switch gear all seem well sealed against dust. The 115mm blue bosch and makita grinders are also very good IME.
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I have a 9" grinder - but it won't fit the stand, which is for 4.5" types. The old Wicks has a plastic case on the gearbox which I'd guess is thicker than metal restricting the depth of cut. But it still works perfectly despite its age - no bearing problems. Just won't do what I want. I'm just off to Toolstation to get a Makita.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Not in stock. Got a Hitachi from Screwfix.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Ya big jessie. Fit ye like?
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There was one of those emergency medical progs on the telly the other night, a person was almost killed by an angle grinder disc shattering when running at speed. I'm really surprised they do not advocate using these inside a suit or armour! My take on your question is that the same grit is there, but one assumes the surface of the material wears as it cuts, so its a bit like pollishing the grit a little bit at a time using the items being cut!
Incidentally, do you wear ear protectors when cutting. i think a neighbour of mine must be deaf by now.
Brian
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"Dave Plowman (News)" < snipped-for-privacy@davenoise.co.uk> wrote in message
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wrote:

No. One should definitely not use an angle grinder inside a suit of armour. If the disc breaks up, the parts will ricochet all around the inside like an armour-piecing round in a tank. With roughly similar results.
Oh! You mean the operator should be inside the suit of armour! As you were then.
Nick
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On Saturday, 8 February 2014 17:47:27 UTC, Dave Plowman (News) wrote:

For mild steel, use thicker discs.
Those extra-thin "stainless" discs have great cut speed and ask less of the grinder. I use them for hand-held stuff on a roof or somewhere awkward, or for tough stainless. However for general slicing and dicing, the older thi ck blades (NB - still cutting, not grinding) last much better.
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I was told on here to use thin ones - less damage to the paint due to heat. I'm not much worried about life given the low cost anyway. Now I'm using the correct technique I'm still on the first one.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Dave Plowman (News) wrote:

I suppose life is cheap in London.
Bill
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