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Fixing shims in vintage Unitron diagonal, help

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#1 Littlegreenman

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Posted 09 January 2022 - 04:25 PM

I have a vintage Unitron diagonal that has 4 shims on the 'bottom" that are loose. The shims appeared to be cut out a 3 or 4 layer sandwich of thin cardboard. I suspect the shims may not be original.  It appears they were glued in place with a light drop of glue, but that no longer works.

Since I have taken it apart  (the third screwdriver fit like a charm)  I thought I would ask:

 

1. a better idea to replace the shims

2. thickness?

3. what kind of glue is a good choice

Thanks ahead of time.

 

 

 

I thought I would ask:

 

 

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Edited by Littlegreenman, 09 January 2022 - 04:27 PM.


#2 ccwemyss

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Posted 09 January 2022 - 04:34 PM

Yes, those are the original shims. I've dealt with a few of these diagonals. Kind of surprising that they didn't use anything more. Most of the time, they stay in place, even without the glue. I did have one where they didn't, because they seemed to have been compressed. I cut a piece of black art paper and put it against the back of the prism, then there was enough pressure to hold them in place (I would have glued them to it, if that hadn't worked).

 

Chip W. 


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#3 Couder

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Posted 09 January 2022 - 04:36 PM

You no doubt know the purpose of the cardboard is to keep the prism in place. All that is needed is for there to be a little pressure exerted. how much is hard to say in words, but you want enough to keep the prism from moving, but not enough to "pinch" the prism. I do not use glue on mine, when you tighten the screws it can't go anywhere.


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#4 Littlegreenman

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Posted 09 January 2022 - 06:35 PM

Thanks to all!



#5 Kasmos

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Posted 10 January 2022 - 12:19 AM

I've yet to take my Unitron diagonal a part, but like mentioned many diagonals just have a thin piece of black construction paper between the prism and the back or the sprung metal tension spring if they have one. Sometimes instead of the spung metal they have a couple of pieces of thin cardboard between the back and the black piece to fill the slack. The ones with larger triangles are usually on the sides and are to keep them centered and/or to protect the prism from the side grub screws. All told, I've never seen evidence of glue in any so far.



#6 Littlegreenman

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Posted 10 January 2022 - 01:29 AM

I've yet to take my Unitron diagonal a part, but like mentioned many diagonals just have a thin piece of black construction paper between the prism and the back or the sprung metal tension spring if they have one. Sometimes instead of the spung metal they have a couple of pieces of thin cardboard between the back and the black piece to fill the slack. The ones with larger triangles are usually on the sides and are to keep them centered and/or to protect the prism from the side grub screws. All told, I've never seen evidence of glue in any so far.

This Unitron has a metal plate on the back side, as seen in my second picture above. There are 4 triangular shaped shims, one for each corner. The plate screws down on top of that. No tension spring. Just the pressure of the plate.

Kinda makes me long for a Lumicon diagonal...

Lumicon collimates each diagonal mirror via a double-pass collimator, according to Lumicon. But they only make 1.25" and 2" sizes.


Edited by Littlegreenman, 10 January 2022 - 01:29 AM.



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