A centrifuge (10) is provided with a cantilevered shaft (18) upon which the main drive rotor (26) is located. A bobbin (62) is attached to the planetary gear shaft (44), which is driven in planetary motion by the rotation of the rotor (26) and its toothed engagement with the shaft (18) of the cantilevered rotor. A flying lead section (72) extends from the bobbin (62) through an aperture in the cantilevered rotor (26). The arrangement provides a centrifuge structure which can handle higher rotational speeds while maintaining resolution. The flying lead section (72) provides a simple path for the inlet and outlet leads (84,86) which reduces dead volume and increases reliability. The bobbin (62) supports at least one coil (68). Rotor component (44) includes at least one bearing (50, 52). Attachment means (66) are provided removably to attach the bobbin (62) to the rotor component (44), the attachment means (66) enabling removal of the bobbin (62) from the rotor without removal of the or any bearing (50, 52) of the rotor component (44). In the preferred embodiment, the attachment means (66) removably attaches the bobbin (62) to an end of the rotor component (44). A gear assembly (40) for the centrifuge (10) is enclosed in a chamber (56) of a rotor (26), which chamber (56) can be provided with lubricant. A chromatography coil assembly is formed from a plurality of rigid substrates (10, 12) which are disc-shaped in plan view. Produced within each substrate (10, 12) is a channel (14, 16) which is closed by the lower surface of the substrate lying thereon, as shown in relation to channel (14). A coupling conduit couples the two channels (14, 16) together to form a unitary coil.