Driven & Static Holders

A static tool holder holds a cutting tool in a fixed position — the workpiece rotates while the tool stays still.

A driven or 'live' tool holder has its own spindle that rotates the cutting tool independently, allowing milling, drilling and threading operations to be performed on a CNC lathe or turning centre without re-fixturing.

Driven tool holders are essential for multi-tasking machines that combine turning and milling!

VDI (Verein Deutscher Ingenieure) and BMT (Base Mount Turret) are the two main turret mounting standards for CNC lathe tool holders.

VDI holders locate via a cylindrical shank and are locked with a serrated ring (common on European machines), whereas BMT holders mount flat to the turret face using bolts, offering greater rigidity for heavy cutting.

The number (e.g. VDI 30, VDI 40, BMT 55, BMT 65) refers to the shank diameter or bolt circle diameter in millimetres.

Always match the holder to your specific turret standard and size!

In order to ensure you select a tool holder that fits your lathe, you need to match up three things:

• Turret mounting standard (VDI or BMT)

• Size (e.g. VDI 40, BMT 65)

• Whether your turret is driven or static only

Check your machine manual or turret face for the standard and size marking.

At MiloTools we stock holders compatible with Doosan, HAAS, DMG Mori, and Mazak machines — use the machine manufacturer filter to narrow down your options, or give us a call on 01274 872822.

The most common collet sizes on driven tool holders are ER 25 and ER 32, which cover tool shanks from 1–16mm (ER 25) and 2–20mm (ER 32).

ER 32 is the most widely used for general milling and drilling on a lathe.

Some holders use an internal (F-type) nut for more compact installation — these are labelled ER 32F or ER 25F in the product specs. Make sure your ER collets match the holder's collet size!

No, you can't.

Driven tool holders require a CNC lathe or turning centre with a powered/live turret. The turret must have a drive spindle that engages with the holder's input shaft to rotate the tool.

On a conventional static turret, a driven tool holder will simply function as a static holder (meaning the tool will not rotate!).

If you're unsure whether your machine has a powered turret, check the machine specifications or contact your machine tool dealer.

The "tool output" is the interface on the driven tool holder that accepts the actual cutting tool. Different cutting tools require different mounting interfaces so the driven holder must match the tool's shank type:

ER Collet nut (ER32, ER40, etc): The driven holder has an ER collet chuck at the output. ER collets are spring collets that grip cylindrical tool shanks (drills, end mills, reamers & machine taps with cylindrical shanks). The collet is compressed by a threaded nut, clamping the tool shank concentrically. ER32 is a common size (for shanks up to 20mm), ER40 for larger shanks. ER collet output is the most versatile (it accepts any tool with a matching cylindrical shank diameter).

Shell-Mill DIN138 (size 22, etc.): The driven holder has a pilot and threaded centre for mounting a shell mill (also called a face mill or end mill with a central bore). The shell mill slides over the pilot diameter and is secured by a centre bolt. DIN 138 is the German standard defining the pilot diameter and bolt pattern. Size 22 indicates a 22mm pilot. Shell-mill output is used for face milling and shoulder milling where a larger-diameter cutter is needed.

Radial Square Tool Holder (25×25): The holder has a square socket (25×25mm) that accepts a square-shank cutting tool. This is typically a static holder configuration (TH-RAD) but can also be driven for live tooling with square-shank tools.

Boring bar holder: A cylindrical socket that clamps a boring bar for internal turning. The bar is held in a collet or V-block clamped by set screws.

Our selection guidance

Choose ER collet output if you use standard cylindrical-shank drills and end mills (most versatile). Choose shell-mill output if you use shell/face mills. Choose square-shank output if your tooling uses square shanks (common for indexable turning tools). The tool output must match the tool you intend to mount (an ER32 holder cannot hold a shell mill and a shell-mill holder cannot hold a cylindrical-shank drill).

Tool orientation describes the direction the cutting tool axis points relative to the lathe spindle centre line:

Axial orientation: The cutting tool axis is parallel to the lathe spindle axis. The tool approaches the workpiece from the end face (drilling into the part centre, end-milling a flat face or tapping an axial hole). Axial holders (LT-S straight, TH-AX) position the tool pointing along the spindle centre line. In a driven holder axial orientation means the driven spindle rotates about an axis parallel to the lathe spindle, so the milling cutter or drill cuts into the end face of the workpiece. Typical axial operations: centre drilling, axial hole drilling end milling, face milling & axial tapping.

Radial orientation: The cutting tool axis is perpendicular to the lathe spindle axis (pointing across the workpiece). The tool approaches the workpiece from the side, cross-drilling a hole through the diameter, slotting across the part or milling a flat on the side of a turned component. Radial holders (LT-A angle 90°, TH-RAD) position the tool pointing across the spindle centre line. In a driven holder, radial orientation means the driven spindle rotates about an axis perpendicular to the lathe spindle, so the milling cutter or drill cuts across the workpiece diameter. Typical radial operations: cross-drilling, cross-milling flats, slotting & radial tapping.

Left/Right designation: Radial holders are often designated L (left) or R (right), indicating which side of the turret the tool extends. This matters because the turret rotates to present each station to the workpiece and the tool must clear both the workpiece and chuck depending on which side it extends.

Our selection guidance:

Choose axial orientation for operations on the end face of the part (drilling, end milling, tapping into the face). Choose radial orientation for operations on the side of the part (cross-drilling, milling flats, slotting across the diameter). Many turn-mill parts require both an axial holder for end-face work and a radial holder for cross-hole work, thus occupying two turret stations.