Workpiece clamping and automation systems specialist 1st Machine Tool Accessories offers
a comprehensive range of high-precision expanding mandrels, both standard and bespoke,
to subcontractors and OEMs in Britain and Ireland. The company is an enthusiastic advocate
of this method of clamping components by their ID (internal diameter) for machining and is
of the opinion that the advantages of expanding mandrels are not harnessed by machinists
nearly as often as they should be.
The standard, modular range comprises manually, pneumatically or hydraulically actuated
types capable of automatically gripping a range of internal diameters from 12.5 to 178 mm.
Each features a generous expansion to accommodate a range of diameters. It is also
possible to grind the gripping surface to suit non-standard bore sizes. Numerous product
adaptations and full turnkey solutions are available to meet especially complex
requirements.
The expanding mandrel is increasingly recognised as a superior work-holding solution for
high-precision CNC turning, cylindrical OD (outside diameter) grinding, and multi-axis
prismatic milling and drilling. According to 1st Machine Tool Accessories, it offers a level of
stability, repeatability and concentricity that is difficult for traditional three-jaw chucks and
standard collets to match. Users can routinely achieve TIR (total indicated runout) below
0.005 mm, a major advantage for precision machining. It compares favourably with values
for a three-jaw chuck, which range from 0.02 to 0.05 mm, or 0.01 to 0.02 mm for a high-
quality collet.
Holding in the ID leaves the entire OD of the part exposed and accessible to the cutter. It
allows the complete machining (in a single set up) of all external features, including
shoulders and complex profiles, as well as the component face. This is unattainable when
external clamping obstructs the surface. Using a previously-machined bore as the primary
datum for subsequent operations, the mandrel ensures accurate concentricity and
perpendicularity with external features.
Unlike external clamping, which can introduce distortions in thin-walled or delicate parts
due to variations in jaw pressure at discrete points around the circumference, the mandrel
provides uniform pressure all around the surface of a bore. Furthermore, for components
with a ground, polished or finished exterior, internal clamping prevents damage to the OD,
preserving the integrity and quality of the final product by eliminating jaw marks, scuffs and
distortion.
In the sub spindle of a bar-fed, twin-spindle lathe, for example, the work-holding technique
provides inherently better alignment of the workpiece and spindle axis, as it eliminates the
eccentricities and jaw pressure variations associated with chucks and the limited gripping
surface afforded by collets.
If a lathe is used for chuck rather than bar work and robot or cobot machine tending is in
place, it is possible to machine slight taper on the end of the mandrel sleeve in the sub
spindle to allow for any small inaccuracy in end effector position during automated transfer
from the main spindle. Exceptionally, if turning tube rather than billet, it may be appropriate
to use a mandrel in both work spindles.
For applications demanding the highest rigidity and accuracy, the advanced design of 1st
MTA mandrels incorporates a double-taper, dual-contact system. This configuration ensures
true parallelism between the workpiece bore and the spindle, eliminating deflection and
chatter during cutting. By engaging the component’s bore at two distinct points near the
front and the rear, the system ensures the component is pulled firmly and squarely against a
precision-ground back face in the mandrel body.
Accurate axial location increases Z-axis repeatability and stability, which is essential for
facing and grooving. The double taper also improves the mandrel’s resistance to torsional
and bending forces generated during machining, allowing higher feed rates and heavier
depths of cut without introducing chatter or runout.
Inherent safety features provide a further advantage. For automated and high-volume
environments, some mandrels are designed to be pre-sprung and only require hydraulic or
pneumatic pressure for release. In these systems, the spring mechanism keeps the mandrel
in its expanded, clamped position by default, preventing accidental loosening in the event of
a power or pressure failure.
For securing particularly long, tubular, thin-walled components up to 1 m in length, or even
more, mandrels can feature multiple sleeve segments, sometimes as many as eight or nine.
The segments distribute the clamping load evenly over a large area, guaranteeing minimal
part distortion while holding components securely to absorb high cutting forces. It is
possible to program the closing sequence of the segments so that they grip sequentially to
ensure positional accuracy.
1st MTA can engineer custom sleeves to hold non-cylindrical features such as splines, gears
or specific internal profiles, extending their applicability beyond simple bores. Whether
turning or grinding, the company says the expanding mandrel delivers not only superior TIR
but also greater grip consistency and longer tool life through reduced vibration, while
lowering set-up time and scrap.
It is less well appreciated that the work-holding solution is suitable for use on machining
centres for securing parts during milling and drilling operations. If a prismatic component
contains a hole, be it circular, square or hexagonal, it is easy to machine that feature first
and then clamp in it using an appropriately shaped mandrel to complete machining of other
features on five sides, again to very precise tolerances.
The high precision and stability offered by expanding mandrels make them essential in
highly regulated and exacting manufacturing sectors where dimensional accuracy and the
integrity of critical components are paramount. The aerospace industry is a prime user,
driven by its stringent quality standards, complex part geometries and reliance on precision.
Expanding mandrels are critical in machining components such as turbine blades, blisks,
aircraft engine parts and structural assemblies, which often feature thin walls, intricate
shapes or require a high-quality surface finish.
The automotive industry, particularly in the production of high-performance vehicles, is
another key beneficiary. Mandrels see use for machining critical powertrain and
transmission components, including parts like crankshafts, camshafts, transmission gears
and steering components, where dimensional accuracy and surface quality directly impact
vehicle performance, noise, vibration and harshness. As the industry shifts towards electric
vehicles, the adoption of expanding mandrels will only increase to achieve the tight
tolerances and consistency required for new electric powertrains.
Beyond these major sectors, mandrels are widely used for applications like gear cutting,
grinding and inspection, railway component machining, and valve manufacture. The
common theme across all these industries is the need for a work-holding solution that can
consistently achieve the highest levels of accuracy, resist heavy cutting forces without
slippage or chatter, and guarantee that the final machined features are perfectly concentric
and square to a previously established internal datum.
More information www.1mta.com
