Diamond cutting discs: safety, use and sharpening

For very hard materials, diamond cutting discs are the right choice. Fitted to an angle grinder, they cut tiles, porcelain stoneware, hard ceramics, granite and slate precisely. To make the disc last, cut cleanly and work safely, there are a few rules. Here you will find the most important safety advice, tips for use and a simple trick to sharpen a blunt disc.

Safety when working with diamond cutting discs

A 125 mm angle grinder usually runs at more than 10,000 revolutions per minute at idle. Mistakes therefore have an immediate effect. Always keep these points in mind:

Before cutting

• Read the operating instructions: Follow the operating instructions of your angle grinder and the information on the disc. These tips do not replace them.
• Change discs safely: Only change the disc with the plug pulled or the battery removed, and fix it with the flanges supplied with the machine.
• Check the permitted speed: The maximum speed stated on the disc must be at least as high as the idle speed of your angle grinder.
• Match diameter and bore: The disc must fit the machine; for 125 mm angle grinders that means 125 mm diameter and 22.23 mm bore.
• Observe the direction of rotation: If a direction arrow is printed on the disc, it must match the machine's direction of rotation.
• Inspect the disc: Do not use discs with cracks, a bent core or missing segments.
• Never remove the guard and adjust it so that it protects you from sparks and fragments.
• Test run: After mounting, let the machine run freely for a moment without standing in the cutting plane. If the disc runs unevenly or vibrates, switch off immediately.

Protective equipment

• safety goggles or face shield
• hearing protection
• Respiratory protection: at least FFP2, FFP3 when dry cutting without extraction. Dry cutting tiles and natural stone produces fine silica dust that can permanently damage the lungs. Where possible, work with an extraction hood and a construction vacuum, and do not blow away or dry-sweep the dust.
• close-fitting work clothes and gloves

While cutting

• Place the workpiece firmly or clamp it; never hold it freely in your hand.
• Guide the machine with both hands and cut straight. Do not tilt the disc or load it sideways.
• Work without excessive pressure and let the disc do the cutting. Too much pressure overheats the disc and increases the risk of kickback.
• Keep other people away from the work area.
• After switching off, wait until the disc has stopped before putting the machine down.

Only cut, never grind

Diamond cutting discs are built for cutting. Grinding sideways with them loads the core across the direction of rotation. The core can bend and the diamond segments wear unevenly. A disc damaged in this way wears faster and can become dangerous on the next cut.

Take cooling breaks

When dry cutting, the disc gets very hot. On longer cuts, let the machine run freely now and then so the air cools the segment. Rather pause briefly more often than cut for too long in one go. You can recognise overheating by a discoloured core and declining cutting performance.

Sharpening a diamond cutting disc

The diamond coating is still visible, but the disc cuts poorly and throws more sparks than usual? Then the surface of the segments is usually clogged. A simple trick often helps: cut the disc into a sand-lime brick up to segment height and make 10 to 20 cuts. The abrasive material exposes fresh diamond grains, and afterwards the disc usually cuts better again.

The right disc for tiles

For tiles and porcelain stoneware, thin discs with a continuous or finely slotted rim are suitable. They cut cleanly and reduce chipping of the glaze. Our professional diamond cutting discs have a segment only 1.1 mm thin and fit 125 mm angle grinders:

• Nivilli Blacky: for short cuts up to 60 cm in heavy ceramics 8 to 30 mm thick, for corded angle grinders.
• Nivilli Whitey: for long cuts from 60 cm in light ceramics 3 to 15 mm thick, for cordless angle grinders.

Frequently asked questions

Are diamond cutting discs dangerous?

An angle grinder with a cutting disc is a tool with a considerable risk of injury. The most common causes of accidents are the wrong speed, a removed guard, tilted cuts and missing respiratory protection when dry cutting.

How do I know a diamond cutting disc is worn out?

When the diamond segments are worn almost down to the core, the disc has reached the end of its life. If the segments are still high but cutting performance is poor, sharpening in sand-lime brick usually helps.

Can I use a diamond cutting disc wet?

Only if both the disc and the machine are explicitly approved for wet cutting. A normal angle grinder is not. Our Blacky and Whitey are designed for dry cutting and are not intended for wet cutting.