diamond cutting disks

[sm_jamieson]

I never had issue with diamond cutting disks before. I got cheap-ish ones, and they just worked. However, yesterday I had about 80 facing brick cross-cuts to make (cutting tapered headers etc), using 230mm disks in angle grinder stand. The first disk was a cheapy "titan" (20 quid) that I had been using for a few months cutting bricks now and then. This was worn quite low and it suddenly stopped cutting, the brick vitrifying as if if there were no diamond left. Off to screwfix to get another titan, since the last had quite a good life. This disk got through 60 cuts OK, and suddenly stopped cutting like the last, although there was loads of the cutting band left, and diamonds could be seen on the sides, but the bottom almost looked "polished" and rounded off. Long story short, another "clarke" disk from nearby machinemart (20 quid) did not appear to even start cutting. I put that down to learning experience (it will cut aircrete !!!). Finally, screwfix, got the Edge GP turbo or something, that took a short while to get going, but then was pretty good (although no better than the titan, although it may last longer). I later read something in the leaftlet that came with the apparently hopeless clarke disk, saying if the disk stops cutting you may need to cut some abrasive material to expose some diamonds. So perhaps this is the problem with all the disks. If so, whats the best mateial to cut to expose some more diamonds ? All the disks were general purpose medium/hard versions. I would probably have been better off getting an expensive disk for hard material including engineering bricks at the start of my building work, but there you are. However, I seem to be lacking some knowledge about the use of there disks. Any tips ? Simon.

[Adrian Brentnall]

In the lapidary (gemstone cutting) business, the advice for rejuvenating a glazed-over diamond saw used to be to make a couple of cuts with the blade into a discarded grinding wheel. The idea was to wear away the edge of the sawblade to reveal a new diamond cutting surface.

I seem to recall that the better blades have a thicker layer of diamonds (which this technique relies upon) - whereas cheaper blades may only have a very thin 'surface layer'of diamonds - and when they're gone you're stuck !

Hope this helps

Adrian

[Andy Dingley]

This is usual for bulk abrasive disks (vitirified or sintered), but not for diamonds.

Bulk abrasive disks can "glaze" on the surface, especially with soft metals and some clays (hard facing or blue bricks). The trick is usually to dress the wheel directly with a diamond or hard steel. Grinding something moderately abrasive (hunk of hard sandstone) can also help.

Diamond disks are differerent - they've only ever had a thin layer of diamonds plated into the nickel surface. If you dig through this, then you've removed the whole diamond layer. The usual failure here is that you've worn the diamonds out, because they're cheap polycrystalline diamonds rather than the natural or high-end synthetic monocrystalline, and you actually broken them in half.

You _might_ still have a problem with glazing the diamonds and occluding them. So it's back to the sandstone lump for a scrub up. Worth trying.

I use Aldi's disks. As good as any other cheap diamond disk (inc Titan), and a lot cheaper.

[Simon]

So a lump of sandstone would be good to try and deglaze ? Any material more readily to hand ? ;-)

Do Aldi do 230mm disks ? I think I've only seen the smaller ones in there. Simon.

[dennis]

Are you sure? The ones I have from lidl appear to have sintered metal "teeth" with diamonds throughout. You get new diamonds as you wear the teeth away. I can't imagine a diamond blade lasting long if it only has a surface coating.

[PeterK]

There is a faq on diamond cutting here

K

[Andy Dingley]

They're not sintered, they're electroplated nickel onto a steel core, with diamond dust captured in the nickel layer.

Sintering is a hot-press process that works for metallic compounds, including metal carbides, that can be persuaded to weld themselves by diffusion bonding. This is the process used for the "knobbly", often gold-coloured, carbide mortar-rake bits.

It is however cheaper to make them that way. Spending more gets you better diamonds (monocrystalline) and in thicker layers. Where I'm buying hand sharpening stones I'll pay good money to get these. When I'm buying angle-grinder disks the quality seems to hold up more than the price drops, so I buy the cheapies. Both Aldi and Lidl have had

9" disks at a smidgen under a fiver.

[Andy Dingley]

Any moderately hard grit in a non-clay binder that doesn't try and vitrify itself. You could probably use limestone, if you're Northerly, just avoid a matrix that's going to gum up faster than it cleans (so no bricks).

[Dave Plowman (News)]

Lidl had them the other week.

[Simon]

They are all described as one of two options, sintered or laser welded. The laser welded ones are the more expensive. But all certainly have more diamonds appearing as the disk wears down. Simon.

[Andy Dingley]

Are those 9" or 12"?

You can't sinter diamonds, but you can mix them with powdered metals and sinter the lot. This is how "diamond disks" have been made for a long time, before the electroplating process became cheap and popular a decade or two back. It's still around, but tends to be for the tiny stuff, or the big and expensive 12"+ stone-cutters. As you suspect, there's diamonds all the way through.

Can't make a whole disk like this, so the segments are made separately and attached. Most are brazed, better ones are laser or e-beam welded. Less heat dumped into the disk means less distortion, so they run truer. You can also "spring" the separate disk blanks (as is done for cicrcular saws) by roller tensioning them, so they stay flatter at speed or when hot. As you are heating things up though, you can't make a solid disk with them and so all of these are segmented (not all segmented disks are attached segments though).

These are all expensive though - they're not in Aldi. Nor are they the usual sort for "angle grinder" use, they're generally either bigger or smaller (you can get them Dremel-sized too, and those frequently are solid unsgemented disks, as they're smaller).

[Simon]

[Ian Zejma]

What some of the concrete drilling guys I have seen working do to recover their drilling barrels on site is to lightly dress the segments with a small angle grinder fitted with a cutting or grinding disc intended for steel. This is ok with slow running core barrels, but with a high rev. disc it would be better to lightly cut into a worn out disc. May be worth a try. Regards, Ian....

remove NOSPAM_ from address

[newshound]

As an old fart who goes back to the times when diamond was only an option if you had NASA-type budgets, the performance of even cheapie disks is astonishing compared with traditional abrasives. The FAQ is right in saying that water is a GOOD THING for tile cutting machines, but in my experience the 300 mm disks in a hand-held grinder will just power through limestone or paving slabs without any water, as long as you have a sense of touch that recognises when you are starting to bind because you have gone off-line. At the smaller scale, the cheap dremel disks have diamond in a chrome? electro plate layer which is very easy to destroy. The screwfix and aldi/lidl disks for 115 and 300 mm grinders are *much* more robust; so far, I havn't actually managed to wear one out (I have to admit that I don't use them all that much, but I sliced up half a dozen 24 inch slabs last week with a 300 mm disk that I bought a couple of years ago, and I think I'm still on my first 115 mm disk after several years too).