An accurately dimensioned convex ellipsoidal surface, which will become a master after polishing, is fabricated from 316L stainless steel. When polishing of the master is completed, it is suspended in a modified watt bath for electroforming of nickel reflectors

Hungerford, W. J.

Larmer, J. W.

Levinsohn, M.

English

NASA Technical Reports Server

Major Axis of Ellipsoidal Master
Head 
hing Cloth 
eumaticTul 
With Polishi 
i-bating b-bean oIisrier 
(Internal View) 
October 1964
	
Brief 63-10547 
NASA TECH BRIEF 
This NASA Tech Brief is issued by the Technology Utilization Division to acquaint 
industry with the technical content of an innovation derived from the space program. 
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Ellipsoidal Optical Reflectors Reproduced by Electroforming 
The problem: Quantity production of high-quality, 
thin-walled, ellipsoidal optical reflectors. For use in 
solar simulators, the inside surface of each reflector 
was required to be an ellipsoid of revolution about the 
major axis. Dimensions were: major axis, 20 inches; 
minor axis, 16 inches; and wall thickness, 1/4 inch. 
The solution: A three-step method involving nu-
merical-control machining of a master, polishing of 
the convex surface of the master to the desired optical 
quality ith a modified floating-head polisher, and 
replication of the concave reflectors by electroforming 
a layer of nickel on the master. 
How it's done: An accurately dimensioned convex 
ellipsoidal surface, which will become a master after 
polishing, is fabricated from 316L stainless steel by 
numerical-control machining. Polishing of the convex 
surface is performed on a modified 36-inch floating-
head polishing machine. The concave polishing head
of the machine, which generally conforms to the shape 
of the master, was modified by installing three inflat-
able tubes (ordinary bicycle inner tubes sufficed) 
around which cloth containing polishing material was 
wrapped, as shown in the illustration. 
The distribution of pressure of the polishing ma-
terial on the surface of the master can be controlled by 
adjusting the air pressure in the tubing. To provide 
relative motion between the polishing head and the 
surface to be polished, the machined ellipsoidal master 
is rotated within the polishing head, while rotation of 
the head is restrained. The head, however, is caused to 
oscillate over a small amplitude in the direction of 
the polar axis (major axis) of the master in order to 
improve the polishing action. 
When polishing of the master is completed as indi-
cated by optical tests, the master is removed from the 
machine and suspended in a modified Watt's bath for 
(cnntin,,ed nverinfl 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States Govern-
merit, nor NASA, nor any person acting on behalf of NASA: A. Makes 
any warranty or representation, express or implied, with respect to the 
accuracy, completeness, or usefulness of the information contained in
this document, or that the use of any information, apparatus, method, 
or process disclosed in this document may not infringe privately-owned 
rights; or B. Assumes any liabilities with respect to the use of, or for 
damages resulting from the use of, any information, apparatus, method, 
or process disclosed in this document.
https://ntrs.nasa.gov/search.jsp?R=19630000101 2020-03-11T16:48:39+00:00Z
electroforming of the nickel reflectors. No difficulty 
has been experienced in removing the electroformed 
reflectors from the stainless-steel master. The compo-
sition of the electroforming bath and operating condi-
tions are as follows: 
nickel sulfate	 35-40 oz/gal 
nickel chloride	 3-8 oz/gal 
boric acid	 5-7 oz/gal 
PH
	
4.0-4.8 
temperature	 125°-135° F 
current	 50 a 
current density	 15a/sq ft 
Notes: 
1. A stress-relieving agent should be added to the 
electroforming bath at intervals during the process-
ing in order to minimize stress in the electroformed 
reflectors.
2. Fine polishing of the electroformed reflectors may 
be necessary in order to remove surface discolora-
tions. 
3. This method can be used for quantity production 
of optical reflectors of other shapes and sizes. 
4. Inquiries concerning this invention may be directed 
to:
Technology Utilization Officer 
Goddard Space Flight Center 
Greenbelt, Maryland, 20771 
Reference: B63-10547 
Patent status: NASA encourages the immediate 
commercial use of this invention. It is owned by 
NASA and inquiries about obtaining royalty-free 
rights for its commercial use may be made to NASA 
Headquarters, Washington, D.C., 20546. 
Source: Maurice Levinsohn, John W. Larmer, 
and William J. Hungerford (GSFC-92) 
Brief 63-10547


Ellipsoidal optical reflectors reproduced by electroforming

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