Prototyping an transparent hyper-hemisphere- ideas?

[salukikev]

Hi,
So I didn't think I'd have as much trouble as I am in prototyping what I've learned is called a "hyperhemisphere" (at least among the SPDT people). Basically a hollow globe with a hole in it around 30-50% of the diameter- similar to a snow globe. In fact, we used a mini glass snow globe in a proof of concept prototype and it worked out okay, but of course there are optical distortions from the blown glass we'd like to get rid of.

My first thought was Single point diamond turning, but evidently that undercut is problematic for that process. I'm thinking about trying a cut & polish on my precision CNC lathe in PMMA, but I'm doubtful I could achieve sufficient surface finish (but maybe an improvement). I'd just bore out the core and then go in with an undercut boring bar. Seems pretty easy (see video).

I'd like to hear of any other options to get myself some prototypes of this part. I know there of at least one resource that can 3d print optics but I don't know if they can do undercuts like that.

 

[IRstuff]

Before anything else, what optical performance are you trying to achieve? That'll determine the level of difficulty and how much money you'd have to spend to achieve that.

TTFN (ta ta for now)
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[MacGyverS2000]

Seems like a good application for a standard molding process... with properly polished molds, the final lenses are surprisingly good. Heck, even $1 Store plastic magnifiers are pretty good for a highly mass-produced item.

If you need anything of true high-quality optics, the usual suspects make them in "bulk"... Meller, II-VI, Edmunds, etc.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[lumenharold]

You might also consider optical silicone. You can get some pretty amazing undercuts and still get the part off the tool. If not by pulling then by blowing it off with air via a retractable pin.

Harold
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nVidia Quadro K5100M

 

[salukikev]

IRstuff:
Let's say typical Commercial optical tolerance as listed here.

Macgyver/lumenharold:
These are good ideas that I should consider, I already have all the materials and setup to do s reasonable test. I would need the end result to be rigid, but I definitely feel like I could pull the core from a mold, and I could mold the core separately to eliminate the seam. I think I may just try this technique. Thanks! Definitely some outside of the box thinking.