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Types of Turret Lathes | Differences between Lathe Turret and Tooling Types

Types of Lathe Turret and tooling

Turrets are not only tools for lathe machine, but also for other types of machine tools. They are used to hold several cutting tools at the same time and allow you to automatically change tools in a set sequence. By combining several operations on the same machine in sequence, the operator can reduce the number of steps required to process parts. This leads to a reduction in production time and a reduction in scrap.

Lathe Turret types

Turrets are divided into the following types:

  • VDI
  • BOT
  • VB
  • BMT

Each type of turret also differs in the maximum number of tools they can hold. There are 8, 12 and 24 position turrets, although some turrets can hold a different number of tools. Most often, modern CNC turret lathes are equipped with 12-position turrets. In this article, we will look at each type of turret in more detail and define the differences between these types.

Verein Deutscher Ingenieure (VDI)

VDI, in the full form of Verein Deutscher Ingenieure, has special holes for mounting tool holders around the outer circumference of the turret. There is a rule: the larger the lathe, the larger the turret is installed. Hole sizes for inserting tools are: VDI16, VDI20, VDI30, VDI40, VDI50, VDI60. Of these, the most used are VDI30 and VDI40, for example, they are used by the popular manufacturer Haas.

VDI toolholders are equipped with a serrated shank that locks the toolholder into the turret holes. Inside each turret there is a mating toothed shaft. To fix the live tooling holders, the shaft must be clamped with a hex wrench. When changing the holder, only one screw needs to be loosened, so changing the tool holder is very fast.

Bolt-On Tool turret (BOT)

This type is well suited for multi-purpose turning centers. The interface has more space inside the turret for the bearings of the driven tool block, providing optimum stability and minimum overhang. BOT turret can not be combined with live tooling.

The BOT tool holders are attached to the turret with four bolts in a radial way. Rectangular external turning tools are installed in the grooves of the turret and are fastened with special clamps, which does not require the use of additional tools.

Unlike VDI, changing the tool holder requires more time, since not 1, but 4 bolts are unscrewed. However, this rigid clamping makes VDI suitable for high volume batch turning. Also, in this variety it is possible to supply coolant through internal channels inside the holder and its rear wall.


As the name implies, this type of turret combines the two previous types. They have both VDI mounting holes and BOT slots in an alternating pattern (6 VDI + 6 BOT). This type of turret allows you to work with both a driven tool and a counter spindle. In this case, the maximum number of holes for built-in tools is equal to the VDI mounting holes.

Base Mount Tooling turret (BMT)

Another type of turret is BMT (Base Mount Tooling turret). In most cases, these types of turrets are installed on Y-axis lathes with driven tools. The tool post drive is located inside the turret, so it does not cover any part of the machine workplace and does not collide with the tailstock. The tool is secured with four bolts and secured in place with four dowels.

It is worth remembering that to avoid damage to the disk inside the turret, the BMT live tool holder collet can only be tightened in the working position and only with two keys or when the tool holder is removed from the lathe.

The shank diameter of the tool holder corresponds to the number in the size designation. For BMT65, the shank diameter is 65mm. 

In order to determine the diameter of the tool holder shank, it is necessary to look at the size designation. This diameter corresponds to the number in the size designation. For example, for BMT65, the shank diameter is 65 mm.


Each type of turret has both its advantages and disadvantages, and the choice of the right type depends on the purpose of the work performed and the machine. Now that you know about the types of lathe turrets, you can learn more about their characteristics and cost in the tool shop accessories.

The VDI turret cannot be used with the counter spindle, but allows the use of driven tools. VDI tool holders are cheaper than others and require minimal effort and time to replace.

The BOT turret is a good choice for a general 2 axis lathe. Radial external turning tools fit directly into the turret slots without the use of tool holders. This type of turret also allows you to work with a counter spindle. The fastening is carried out on 4 bolts, which provides a strong fixation of tools, and makes the BOT turret suitable for large machines.

The BMT turret is often mounted on a turning center with a driven tool. The drive is hidden inside the turret and does not interfere with processing. The use of radial and axial tool holders allows the use of both the main spindle and the counter spindle.

Thanks to the combination of two types VDI and BOT, VB allows you to work with both a driven tool and a counter spindle.

About the author

Jamie Moses

Jamie Moses founded Artvoice in 1990

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