We have constructed a large differentially pumped platform for use in ultrahigh vacuum. The design utilizes spring‐loaded Teflon seals to permit differential pumping between two horizontal stainless‐steel disks. This allows the rotation of the upper disk and the items built into it directly inside a vacuum chamber while maintaining a pressure of 2×10−10Torr. The following design parameters are discussed: conductance across the seals, deflection of the seals, rotational friction, and differential thermal expansion during bakeout.