Hi James,
I took the liberty of asking Joerg Woerner of the Datamath Calculator Museum the same question as posted here earlier. And here is some revealing news. I hope you will read this before you see your guy tomorrow perhaps you can put it to some good use.
Here's what Joerg said about the process of making the original TI calculator bubbles :
Hello Chaim,
Good observations – now I can really apply some knowledge I aquired
I’m an engineer at Leuze electronic and our products always combine electronics and optics. Most of our products use plastic molded lenses, something I know about!
The Exactra lenses are plastic molded parts and tooling is not easy. A tool is either cheap or has good optical surfaces. But we need for the Exactra only a small portion “optical quality”, the remaining part is just for easy handling and fixture on the PCB. What they did is a cheap tool for the part with a so-called insert for the lens surfaces. An additional part of polished steel “inserted” into the cheap “main tool”. What you observe is the “dividing line” between these two parts of the tool. They used probably one tool with two different inserts, 9 bubbles and 7 bubbles. Frozen or not? Easy, too: Sometimes depending on where or when it was manufactured, the toolmakers choose a rough surface of the non-optical parts of the tool.
Greetings from New York,
Regards,
Joerg
So it seems that all the calculator bubbles real and replicated should have flattened edges!
Lots of success with replicating your Exactra 20 James.
Chaim
P.S. At least I know that Joerg would be very pleased if no more still functioning Exactra's were destroyed when there's a perfectly goodlooking replica that would please all of us just the same as the real thing hence the reason why mine are still intact even both my Graflex Flashguns haven't been modified into lightsabers .... yet :angel :confused ... but they will be ... they will be :lol