cr 39 shrinkage

[ioptic]

Hi all,

I am trying to work out the radius compensation for cr39 shrinkage - when casting cr lenses.

..say I want a cr lens surface of radius 100mm - I expect to use a glass mould surface of 116mm radius (been told cr39 shrinks by 16%- from its liquid stage).

Does anyone have a more relable way to judge the shrinkage. There appear to be quite a few variables- due to moisture content of air etc... curing method used- heat applied, degassing, second curing stage, or simply manufacturers data sheet data etc...

So it looks to me more like a processed based on experience, rather then a predictiable process based on reasoning :)


All clues greatfully received.

Season's greetings to all !

ROb
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[Jacqui]

So it looks to me more like a processed based on experience, rather then a predictiable process based on reasoning :)

yup. Just do it and learn.

[ioptic]

yup again- getting one's hands dirty always beats chin wagging :)

rob
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[Darryl Meister]

Your best bet is to actually cast some lenses and then compensate the molds accordingly.

[ioptic]

Thanks for the tip- tis saves me many agonising hours of useless theorising :)

I see postings of 14-16%, ut when I halt to guys, they always whing it !

Many thanks
ROb
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[Chris Ryser]

So it looks to me more like a processed based on experience, rather then a predictiable process based on reasoning :)

You just solved your problem.
Only if the exact same conditions are in force at all times you will have the same shrinkage at all times.

[ioptic]

Thats chemical reactions for you :) change the input and you change the output ...

I guess thats why in-house casting has such a bad reputation. I once saw an MC machine 1 foot away from a water based splashing plolisher! I am still wondering if they ever got a consistant coating :)

best regards
ROb
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[mauroventura]

Hello Ioptic,
i am interest to know if in your CR-39 cast procedure , you follow also the preparation of the cr39 monomer with the catalyst .

[ioptic]

Hi,

yes - the works:)

best regards
ROb
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