How to Use a Floating Head Diamond Drag Bit for CNC Engraving

By Premium CNC & Router Bits for Precision Cutting | Published: 2026-10-23

Category: How-to Guides

Learn step-by-step how to set up and run a floating head diamond drag bit on your CNC router or mill for clean engravings on metal, plastic, glass, and stone.

Quick answer

A floating head diamond drag bit engraves by scratching the surface, not cutting it. Set a shallow Z depth, let the spring-loaded tip follow material variations, and use slow feed rates for crisp results.

Why use a drag bit instead of a rotary engraving bit?

A floating head drag bit doesn't spin to remove material. It uses a diamond tip to scratch a fine line (~0.005″ wide) as the CNC moves the bit across the surface. This produces no chips, dust, or burrs, making it ideal for finished parts, thin sheet metal, and delicate materials like glass or granite.

Because the bit has a spring-loaded floating head, it can follow slight surface unevenness without breaking the tip or cutting too deep. That makes setup simpler than with a standard engraving bit, but you still need to get the Z-zero and feed rate right.

Choosing between 1/4″ and 1/2″ shank

Both shank sizes work in any CNC router or mill that can hold them. The 1/4″ shank is more common in hobby routers and smaller spindles; the 1/2″ shank offers extra rigidity for production work or large-format machines. Neither changes the engraving performance—the tip and spring assembly are identical.

Step-by-step drag bit setup and engraving

1. Install the bit and set Z-zero on the work surface: Insert the drag bit into your collet and tighten securely. Lower the tip until it just touches the material surface. Set your Z-zero at that point. Common mistake: setting Z-zero on the table instead of the work surface, which risks engraving too deep or breaking the tip. Always set Z-zero on the actual workpiece, not the spoilboard.
2. Set a shallow engraving depth (0.005″–0.010″): In your CAM software, set the engraving depth to 0.005″–0.010″ below the surface. The floating head will compensate for slight variations. Going deeper than 0.010″ can cause the tip to drag or break on hard materials.
3. Use a slow feed rate (30–60 in/min for metals, 60–100 for plastics): Start at 40 in/min for aluminum or steel, and 80 in/min for acrylic or brass. Too fast and the tip skips or produces a faint line; too slow risks burning on plastics. Adjust based on your machine's rigidity. Test a short line first, then adjust feed rate in 10 in/min increments.
4. Run a single pass—do not use multiple passes: The drag bit scratches the surface; multiple passes will widen the line unevenly and may dull the diamond tip prematurely. One pass at the correct depth and feed rate gives the cleanest result.
5. Check line quality and adjust tip angle if needed: The included 120° tip produces a wider, shallower scratch. If you need finer detail or deeper engraving on hard metals, switch to the optional 90° tip (sold separately). A common mistake is using the 120° tip for tiny text on steel and getting a blurry result. Buy the 90° tip for small lettering or deep marks on hardened steel.

Recommended drag bit

Diamond Drag Engraving Bit x 1/4″ Shank – Widgetworks (250-CNCDRAG): Use your CNC router or CNC mill to diamond drag engrave plastics, brass, aluminum, steel, glass, and granite. Shank Diameter: 1/4″. Engraved Line Width: ~0.005″. Includes 120° tip; 90° tip sold separately. The 1/4″ shank fits most hobby CNC spindles, and the included 120° tip gives a clean, fine line on metals and plastics without needing a separate purchase.
Diamond Drag Engraving Bit x 1/4″ Shank – Widgetworks (250-CNCDRAG)