Services & Support: Polishing/Inspection, Custom Engineering



In the assembly of an ultracentrifugation cell, the sample holder (centerpiece) is compressed between two quartz or sapphire windows. Since this arrangement is exposed to high centrifugal forces, imperfections on the component interface can lead to leakage and loss of sample. Even when components are handled carefully, long-term use can result in minor scratching and abrasive pitting of the centerpiece. Careful analysis of damage and polishing of the centerpiece surface can restore proper performance of the assembled cell.

Pre-inspection Report

All centerpieces sent for polishing are inspected prior to polishing. Each centerpiece is carefully inspected with a toolmaker’s microscope and measured with precision indicators. The pre-inspection report includes measurement of the thickness of the centerpiece, the flatness of both faces, the rim depth, and the perpendicularity of each face to the centerpiece side. Any visible damage to the surface, channel interior, and septum are also noted.

The purpose of the pre-inspection is to determine whether or not the centerpiece is a candidate for repolishing. Occasionally, damage to the centerpiece is too severe to allow surface restoration through polishing alone. If a centerpiece does not pass the pre-inspection the customer will only be billed for the inspection.

Polishing Procedure and post-inspection report

Centerpieces which pass the pre-inspection will be polished with our power polishing machines. A series of abrasives are used to produce the best finish on each piece. The minimum allowable rim depth after polishing is 0.005”. After polishing, a post-inspection report is produced and returned with the newly polished centerpieces. The report includes a precise measurement of the centerpiece so that accurate concentration computations can be made from absorbance measurements.

Surface Restoration

If a centerpiece fails pre-inspection, it may be possible to restore the surface by remachining the surfaces. This service can be useful if the surface defects are too deep to polish out or if doing so would eliminate the rim and not allow the window to seal properly. Rather than discarding the centerpiece, it may be possible to machine the centerpiece with a precision lathe and then polish the new surface. The centerpiece thickness will be smaller than the nominal thickness but we report the new thickness in the post-inspection report so that precise calculations of concentration from absorbance values can be made. This service is an additional charge over the standard polishing price.


Engineering Services Available Include: