Spin casting is a technique for constructing large
parabolic mirror
A parabolic (or paraboloid or paraboloidal) reflector (or dish or mirror) is a reflective surface used to collect or project energy such as light, sound, or radio waves. Its shape is part of a circular paraboloid, that is, the surface generated ...
s by using the curved surface formed by a rotating liquid (e.g. in a
rotating furnace
A rotating furnace is a device for making solid objects which have concave surfaces that are segments of axial symmetry, axially symmetrical paraboloids. Usually, the objects are made of glass. The furnace makes use of the fact, which was known alr ...
).
It is distinct from the
spin casting
Spin casting, also known as centrifugal rubber mold casting (CRMC), is a method of utilizing inertia to produce castings from a rubber mold. Typically, a disc-shaped mold is spun along its central axis at a set speed. The casting material, us ...
or centrifugal rubber mold casting (CRMC) technique used for casting metal or plastics.
Pioneered by
Roger Angel
James Roger Prior Angel (born February 7, 1941) is a British-born American astronomer. He is Regents Professor and Professor of Astronomy and Optical Sciences at the University of Arizona.
Education
He graduated from St Peter's College, Oxford, ...
at the
Steward Observatory
Steward Observatory is the research arm of the Department of Astronomy at the University of Arizona (UArizona). Its offices are located on the UArizona campus in Tucson, Arizona (US). Established in 1916, the first telescope and building were f ...
's mirror lab, this makes large () thin parabolic mirrors by spinning the oven as the glass is melted and cooled.
The term is applied to the fabrication of large
telescope
A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to observe ...
mirrors, where the natural
paraboloid
In geometry, a paraboloid is a quadric surface that has exactly one axis of symmetry and no center of symmetry. The term "paraboloid" is derived from parabola, which refers to a conic section that has a similar property of symmetry.
Every plane ...
curve followed by the molten glass greatly reduces the amount of grinding required. Rather than being cast by pouring glass into a mold (with top and bottom), an entire turntable containing the peripheral mold, and the back pattern (a honeycomb pattern to lighten the finished product) is contained within a furnace and charged with the glass material used. The assembly (or
rotating furnace
A rotating furnace is a device for making solid objects which have concave surfaces that are segments of axial symmetry, axially symmetrical paraboloids. Usually, the objects are made of glass. The furnace makes use of the fact, which was known alr ...
) is then heated while spun at slow speed until the glass is liquid, then gradually cooled over a period of months.
See also
* technique
*
References
Bibliography
* Goble, L. W., et al. "Spincasting of a 3.5-m diameter f/1.75 mirror blank in borosilicate glass." Advances in Fabrication and Metrology for Optics and Large Optics. Vol. 966. International Society for Optics and Photonics, 1989.
* Hill, J. M., and J. R. P. Angel.
The Casting of the 6.5 m Borosilicate Mirror for the MMT Conversion. European Southern Observatory Conference and Workshop Proceedings. Vol. 42. 1992.
External links
Optical Fabrication in the Large p. 6
*
ttp://www.math.udel.edu/~pelesko/PBLOG/Team_3_spin_017.pdf An investigation into the spin casting processA Telescope Made of Moondustincluding a citation to 1966!
Wonderings On Spin Casting Parabolic Mirrors
Telescopes
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