Am 18.04.2013 09:48, schrieb Gregg Eshelman:
> How are molds for plastic reflectors machined? They have a large number of 
> sharp edged corner cubes.
>
> Could be done with EDM, but how would the EDM electrode be machined? All 
> those small facets have to be polished for the reflector to reflect light.
>
> Plastic reflectors have been made like this as far back as 1952. Before that 
> there were ones with larger corner cube patterns molded in glass.
>
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Gregg,
at first, I wondered where the corners in your reflectors are. Of 
course, I thought at  paraboloid shapes, aluminum coated by sputtering 
and highly reflective. The mold would be easy to make on a lathe. But I 
suppose, you are speaking of what we call cat's eyes, passive 
reflectors. These are reflective not for their polish, but because of 
total reflection on the transition from glass (plastic) to the air. The 
surfaces don't have to be extremely smooth. They are made by three 60 
degree criss-cross milling cuts with a 90 degrees tipped milling tool or 
on a shaping machine (which yields better surfaces for this purpose).

Peter

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