Expanding Mandrels | Kitagawa
Kitagawa Middle East

Expanding Mandrels

KEM Series

KEM Expanding MandrelGripping a workpiece by its inner diameter (ID) rather than its outer diameter (OD) is a workholding option that many job shops fail to consider when turning or grinding parts. However, this technique offers a number of advantages, especially in the machining of workpieces with complex surfaces. Kitagawa Europe produces a series of CNC expanding mandrels designed for a range of spindle types that offer more flexibility in workholding than people might think.

The expanding mandrels can be used to grip any workpiece that has a suitable inner bore diameter and which lends itself to being completely machined on the outside. The suitability of a workpiece’s inner bore is application-specific; We generally advise that there be, at most, a 3:1 length-to-diameter ratio of the inner bore. However, it is possible to accommodate higher ratios depending on a variety of factors, such as the type of material being machined or the aggressiveness of the cut.

Expanding mandrels are especially useful when a workpiece requires secondary machining operations because these devices enable external diameters to be turned in a single operation, increasing concentricity between the two operations. They also prevent damage to previously machined surfaces, which is why expanding mandrels are often used on lathe sub spindles. The access they provide to a workpiece’s entire outer surface also makes them well-suited for use on lathes with live tooling.

Another possible application is when a part has a lot of external features or there are changes in its diameter. In this case, the available gripping length of the OD may be limited. However, if the workpiece has a suitable inner bore, an expanding mandrel can be used to grip the workpiece along a significant length on the ID, therefore increasing engagement with the mandrel and rigidity of the hold. This is especially applicable in industries such as gear-making.


Kitagawa Europe's expanding mandrel systems are made of three major components. The first is the body, which acts as the interface to the machine tool and contains a threaded piece called the drawtube connector. This connector can be custom-machined to each individual machine’s drawtube. This helps to simplify installation of the mandrel system onto the machine. The second major component contains three individual parts: an adaptor that connects an expanding pin to the drawtube connector, the expanding pin and the mandrel itself. The mandrel contains a male taper that corresponds to a female taper on the third main component of the system, which is the expanding sleeve. The systems works by sliding the expanding sleeve over the mandrel, locking it into place with a pin and drawing the mandrel back axially using the machine’s drawtube. This motion pulls the expanding sleeve further back onto the mandrel causing the two tapers to interface and the mandrel to expand.

One key feature of Kitagawa Europe's line of CNC expanding mandrels is that the segments of the sleeve are able to expand in parallel, maintaining contact with the workpiece over their whole length in order to eliminate the risk of distortion, particularly with thin-walled parts. This parallel grip also increases accuracy, grip force and torque transmission.

However, it is the combination of features that makes our expanding mandrels stand out.

The line is standardised on most common gripping ranges and spindle types, and the company maintains a database of machine tool spindles and drawtubes to enable customization of drawtube connectors. Additionally, Kitagawa Europe offers a number of specialized systems to fit each company’s individual needs. Kitagawa Europe can supply systems with multiple expanding sleeves or mandrels that can support workpieces with IDs as large as 635mm. Although typically used in turning or grinding applications, our expanding mandrels can be adapted for use on milling machines with special fixtures as well.

The standard line of CNC expanding mandrels consists of five possible mandrel models with four different body assemblies. The mandrel models are determined based on the ID of the workpiece and its corresponding gripping range, while the body assemblies are based on the four most common spindle types: A2-5, A2-6, 140mm and A2-8. KEM-A features a gripping range of 12.4mm to 22.4mm, KEM-B ranges from 15.9mm to 29.1mm, KEM-C ranges from 21.9mm to 40.3mm, KEM-D from 28.3mm to 51.5mm and KEM-E ranges from 41.1mm to 82.7mm. Expanding sleeves are sold separately in a variety of gripping ranges. Optional part locators are available if required.


KEM Series includes a manually-operated expanding mandrel actuator (KEM-MA) incorporating a precision-ground 38mm diameter location spigot that enables the unit to be held in any collet or jaw chuck, reducing setup times by eliminating the need to change the machine’s three jaw chuck or collet chuck.

These models utilize the same precision mandrels, expanding sleeves and locators as our CNC Expanding Mandrels

This unit is side-actuated with an included square-drive key that means this unit can accommodate parts with blind bores as well as those with thru-holes. The KEM-MA is precision-ground for high accuracy in squareness and concentricity. If higher accuracy is needed the mandrel can be clocked-in once the unit is gripped in a chuck. A universal location spigot mount enables this ID workholding system to be easily moved from machine to machine as jobs require.

The KEM-MA is perfect for low/medium-volume production but for high-production environments, use of the CNC Expanding Mandrels is recommended.