Restoration of NIST's million-pound deadweight machine

Restoration is well underway for NIST's 4.45-million newton (equivalent to one million pounds-force) deadweight machine, the largest in the world. The three-story-tall deadweight, comprising a stack of stainless steel discs weighing about 50,000 pounds each, was disassembled last winter for the first time in fifty years.

The surfaces of a half dozen components of the deadweight recently underwent minor machining at NIST and by a company offsite, to permit more free operation at those interfaces. Pieces that were sent offsite returned to NIST in June fully restored.

The final task remaining before reassembly is recalibration of the approximately 50,000-pound discs.

Force measurements require an accurate assessment of mass. Since the international standard for mass is the kilogram (kg), PML staff members begin their calibrations with standard masses of this size (1 kg is slightly more than 2 pounds). They then work their way from 1 kg weights to standard weights that are tens of thousands of pounds, making a continuous chain of mass comparisons using progressively larger standards.

This recalibration process began in late spring and will take several weeks to complete.

Built in 1965, NIST's million pounds-force deadweight system consists of a calibrated lifting frame and a stack of 19 stainless steel discs about three meters in diameter (a little less than ten feet) when assembled. Their average mass is about 22,696 kg (just over 50,000 pounds) each.

Customers who rely on this unique machine include US aerospace manufacturers, US military laboratories, and several top-end commercial force calibration labs, which have performed hundreds or thousands of calibrations, all directly traceable to NIST.

The NIST million-pound deadweight system is expected to be back online this year.

• 

• 

• 

•