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Prism Cementing

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Optics Apprentice
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DPI Quote  Post ReplyReply Direct Link To This Post Posted: April/05/2020 at 02:15
Ok! So that worked, as far as it goes. However the Canada Balsam has a tendency to migrate to the lower end, leaving a void at the top between the two prism surfaces. Gravity you know.

This could be due having diluted the balsam too much, it was 2:1 Xylene/Balsam mix.

Two possible solutions.

1. Use a less dilute solution.
2. Redesign the support to allow a more horizontal support configuration.

Well I don't have the remainder of my Balsam supply with me and under the current movement restrictions, not going to have access for some time. So it looks like option two is the way to go for the moment.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote DPI Quote  Post ReplyReply Direct Link To This Post Posted: May/15/2020 at 12:27
The continuing saga and for general information that others might find useful, certainly I have not found anything on the subject.

In the interests of pure curiosity, I began looking at using LOCA glue for cementing prisms.

Certainly optically it serves the purpose nicely, but what if it all goes wrong, what to do?

To this end, I used LOCA (type TP-1000N)  to cement a set of prisms, curing it using a UV 395nm torch that came with it. The torch ran of a single AA 2900 Ah battery. I went through two batteries before the curing set, even then it was not fully set, this caused the LOCA interface to be less clear than is useful.

Occluded areas, striations in the media. Frankly not very useful, but it was expected as I had no real faith in the torch that came with it. How to separate and resolve the problem then became the issue.

There are LOCA remover compounds, both general and specific on the market. Most of these consist of Isopropyl or acetone solvents, other solvents might also be useful. But it seems that some LOCA are susceptible to some solvents and not others. This is not always identifiable as to which is which, so was there another way that could be applied more generally?

LOCA being essentially a thermoplastic, the obvious first consideration was the application of heat, but how much and how?

Well back to the microwave.

After various tests, I found that using an 800watt oven set at max for;

Five minutes, did nothing except make it hot.
Eight minutes, pretty much the same.
Twelve minutes, the prism separated stickily but easily.

So it appears that to separate a badly set prism, it can be achieved with a microwave. Cleaning the LOCA residue is another problem, but at least addressable now that they are separated.

Hope you found this of interest and useful.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DPI Quote  Post ReplyReply Direct Link To This Post Posted: May/15/2020 at 12:30
Oh Addendum:-

Important safety note:

Do not use kitchen paper towel as a substrate. The glass gets really, really hot and scorches it, any longer it might have caught fire.




Edited by DPI - May/15/2020 at 12:36
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