DeWalt EXTREME Twin Diamond Blade for Joints, 125 x 22.23 mm, DT3758

DeWalt EXTREME Twin Diamond Blade for Joints, 125 x 22.23 mm, DT3758

DeWalt DT3758-QZ is a twin diamond blade from the EXTREME Segmented range, 125 mm in diameter with a 22.23 mm bore. Maximum speed is 12,000 rpm (80 m/s) and the blade is for dry cutting only. It conforms to EN 13236.

Why there are two blades

The article contains two blades mounted side by side with a spacer between them. This is not about doubling the blade's life - the two blades cut two parallel kerfs at once, and the material between them is knocked out with a chisel or cleared with the machine. The application is specific:

• Raking out mortar joints in masonry - in restoration and before repointing, the old mortar is removed to the full depth of the joint
• Chasing channels for electrical installation and pipework in brick and concrete

A single blade requires two separate passes and precise parallel alignment; a twin blade does both at once and gives a guaranteed constant width along the whole length of the chase.

Segmented rim

The rim is segmented, with gaps between the segments. For dry cutting that is mandatory: the gaps admit cooling air to the segment and carry dust out of the cut. A continuous-rim blade cut dry overheats within seconds. The segments are laser welded to the body rather than sintered - at the temperatures of dry cutting, laser welding is what keeps a segment attached.

Dry cutting only

The blade carries a symbol prohibiting the use of water. The reason is practical rather than structural: when chasing a wall, water turns the dust into slurry that clogs the chase and runs down finished surfaces below. These blades are therefore used with dust extraction, not with water.

Materials and applications

The blade is intended for masonry and concrete - brick, block, cement mortar and softer concrete. The symbols on it show exactly that: a wall and a mortar joint. Reinforced concrete and hard granite call for a different class of blade.

Mounting and speed

The bore is 22.23 mm - the standard for 115 and 125 mm angle grinders. The 12,000 rpm maximum covers any grinder in that class, but it is worth checking: a faster machine must not be used. When fitting, the spacer between the two blades must be in place and centred - without it the blades touch and destroy each other.

Safety

Working with a twin blade in a wall is among the riskier angle grinder operations: the kerf is wide, the machine is prone to kickback if it binds, and the dust is heavy. Eye protection, a dust mask, hearing protection and gloves are essential. Use the machine's guard and dust extraction. Never remove the guard to "see the cut better".

Technical specifications

Questions and Answers