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NIST

Metrology

A Million Pounds of Accuracy

Restoring the largest deadweight machine in the world

Published: Wednesday, July 29, 2015 - 17:12

Restoration is well underway for NIST’s 4.45-million newton (equivalent to 1 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 50 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.


Minor machining of a component offsite. Image courtesy of Precision Custom Components LLC

 


A restored component of the million-pound deadweight machine being returned to NIST in June 2015

 


Lowering a restored component off of the truck. The four pieces that were machined offsite are approximately 1.83 m (about 6 ft) in diameter and weigh approximately 3,674 kg (about 8,100 lb) each.

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


Before: Restoration was required to repair galling near the bottom of the conical “doughnut hole” in the middle of this weight.

 


After: Shining restored the surface of one of the weights sent offsite for minor machining.

Force measurements require an accurate assessment of mass. Because 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 2015 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 3 m in diameter (a little less than 10 ft) when assembled. Their average mass is about 22,696 kg (just over 50,000 lb) each.


NIST’s 4.45-million newton (one million lb) deadweight machine when fully assembled

Customers who rely on this unique machine include U. S. aerospace manufacturers, U. S. 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.

See “Restoration Begins on NIST’s Million-Pound Deadweight Machine” for additional photos depicting the recent machining of several components of the weights and their return to NIST.

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NIST

Founded in 1901, the National Institute of Standards and Technology (NIST) is a nonregulatory federal agency within the U.S. Department of Commerce. Headquartered in Gaithersburg, Maryland, NIST’s mission is to promote U.S. innovation and industrial competitiveness by advancing measurement science, standards, and technology in ways that enhance economic security and improve our quality of life.