Calculating the Effect of the Addition of a Plastic Washer to the Stack of Belleville Springs in the SDSS Camera Stirrup

Sloan Digital Sky Survey Telescope Technical Note 19970724
Larry Bartoszek

The insulating washer that is contemplated is 1.1" O.D. X .5" I.D. thick, and made out of ulteum 2300 resin.

EUL = 938,000 psi, compressive modulus.

The spring constant of a washer may be calculated from the stress-strain relationship:

I will assume that metal washers allow the load to be distributed uniformly over the plastic washer.

The spring constant for the stack of Bellevilles comes approximately from the information that the stack deflects .204 inches at a load of 971.8 lbs (See "Calculating the Parameters of the Disk Springs in the SDSS Camera Stirrup Mechanism," L. Bartoszek, 4/2/97)

The stack is a much softer spring than the plastic washer. What is the change in the overall spring constant when the stack is in series with the washer?


The addition of the plastic washer insignificantly reduces the effective spring constant.


Questions regarding this note should be addressed to Larry Bartoszek by phone at (630) 844-0248 or by e-mail at

Last modified 04/28/99