Diamond blade that no longer cuts: the bond and the material

“The blade is brand new and it won't go into the granite.” The blade was a good one, but it was made for brick. On the hard material its diamond has rounded off, the bond hasn't worn away, and the blade has started to rub instead of cut. It happens all the time, and the answer is not to push harder.

How a diamond blade cuts

A diamond blade has no teeth. It has diamond grit held in a metal bond. The grit scratches away the material and wears down, and the bond around it has to wear away just enough to expose fresh grit. If the bond holds out for too long, the old diamonds stay there, worn smooth, and the blade doesn't cut. If it wears too fast, the blade doesn't last.

The rule that seems back to front

• Hard material (granite, porcelain stoneware, very dense concrete): you need a soft bond, one that opens up easily and exposes new diamond.
• Abrasive material (brick, green concrete, asphalt, refractories): you need a hard bond, otherwise the material itself wears the bond away and the blade is eaten up in a few metres.

That is why there is no single blade that suits everything equally well. The “multi-purpose” ones are a handy compromise on site, but for a specific job a dedicated blade cuts better and lasts longer. In the collection you will find Rubi, Bossong, Sea Technology, Breaker, DeWalt, Makita and Unifix, with different lines for ceramic, cement, brick, hard materials and asphalt.

Continuous rim, turbo or segmented

The continuous rim gives the cleanest cut, without chipping the glaze: it is the one for ceramic and porcelain, often used wet. The turbo has a wavy rim: it cuts faster and stays fairly clean, which makes it the compromise for mixed materials. The segmented blade has gaps between the segments that clear dust and heat: it is the one for concrete and brick, even dry. On segmented blades for dry cutting, check that the segments are laser-welded, because they stand up to heat better.

Cutting dry: let the blade breathe

Dry cutting should be done in bursts: a few seconds of cutting and then a few seconds with the blade spinning in free air to cool it. If the blade turns red or changes colour, you are ruining it. A blade made for wet use must be used with water, with no exceptions.

Glazed blade: it can be dressed

When the blade slows down, throws sparks or heats up and the rim looks shiny, it is probably glazed. You can dress it by making a few cuts in an abrasive material, such as a brick or a dressing stone: the bond opens up again and the diamond comes back out. If instead the rim is worn right down to the body, the blade really is finished.

Three things I see at the service desk

• Blade fitted the wrong way round: the arrow on the blade must follow the direction of rotation of the machine.
• Blade used on its side to bevel an edge: a diamond cutting blade works only with its cutting edge.
• Construction-grade diamond blade used on steel: the rim is ruined in a few seconds, apart from blades declared suitable for metal as well.

What I need to know

Tell me what material you cut and how often, what machine and what diameter, whether you cut dry or wet, and whether you need a clean cut or just a fast one. With that information I'll suggest the right bond and rim, instead of yet another multi-purpose blade.

We have these in store

A selection from the range we hold. If you can't find the size or model you need, just ask: what you see online is only part of what we can source for you.

XHUDD diamond disc - hard materials - high performance MilwaukeeMilwaukee SUDD diamond disc - silenced - hard materials MilwaukeeMilwaukee HUDD diamond disc - hard materials MilwaukeeMilwaukee DUT diamond disc - soft materials MilwaukeeMilwaukee DUH diamond disc - hard materials MilwaukeeMilwaukee DU diamond disc - soft materials MilwaukeeMilwaukee

See the whole category: Diamond Cutting Discs