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Go Back   IceInSpace > Equipment > ATM and DIY Projects

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  #1  
Old 17-01-2019, 09:52 AM
scoperboy (Stuart)
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Removing glued/siliconed primary

Hi there
I have an issue with astigmatism and I am trying to solve, but I can't free up the primary to rotate it etc and check its not a primary cell issue. Its an Orion optics UK primary, 30cm F4, in a home made wooden cell.

It is siliconed to a wooden cell in about 6 blobs. The clearance is about 1mm between the back of mirror and cell

So far I have tried cutting with blade, using braided wire as a saw, and tipping acetone all over it (as I have no vessel large enough to sit the mirror in acetone)
THe wire sort of worked, but there is barely enough space to move in behind there and I went through 7m of wire and only got maybe 20% through the silicone/glue/whatever the awful stuff is.

Any more ideas to remove it? I am out of ideas except for sawing the cell into pieces, and chiselling off

Note: Coating is pretty much done for, only care about retaining it a little bit for the purposes of re-testing the astigmatism issue, once the primary is removed from the cell and I am able to rotate it etc.

thanks
Stu
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  #2  
Old 17-01-2019, 09:59 AM
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multiweb (Marc)
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Razor blade than stanley knife to cut the silicon then clean it all up. Maybe you've cut enough to release the pressure and your astigmatism may have gone already. Check it out again.
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  #3  
Old 17-01-2019, 10:07 AM
scoperboy (Stuart)
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Quote:
Originally Posted by multiweb View Post
Razor blade than stanley knife to cut the silicon then clean it all up. Maybe you've cut enough to release the pressure and your astigmatism may have gone already. Check it out again.
Tried Stanley blade but doesn't really reach in far enough, and due to the hardness of the stuff and the lack of clearance, you don't really get very far.

I did think about retrying it. Im fairly confident the astigmatism is coming from the primary.....
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  #4  
Old 17-01-2019, 10:14 AM
Wavytone (Nick)
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Find a handsaw with a blade long enough to cut right across the back of the glass, parallel to the glass, and cut through all the silicone. You're up for a new cell anyway by the sound of it.

The blade can't do any damage to glass - more likely the glass will take the edge off the blade.
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  #5  
Old 17-01-2019, 10:50 AM
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mswhin63 (Malcolm)
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Try a thin stainless wire multi core and saw through the silicon. The multi strand may provide a cutting action where a single strand may not cut as well.
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  #6  
Old 17-01-2019, 11:00 AM
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Or maybe a hack saw blade, they are quite long and use on with 24 teeth to the inch.
I reckon that would work, and whilst cutting try and get some WD 40 in there to help the process, just my 2 cents worth.

Leon
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  #7  
Old 17-01-2019, 12:20 PM
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multiweb (Marc)
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+1 hacksaw blades work well. Forgot about that. You won't harm the glass.
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  #8  
Old 17-01-2019, 01:39 PM
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Merlin66 (Ken)
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I agree, in your situation, with the hacksaw blades.
I've seen this silicon remover, but never used it.
https://www.bunnings.com.au/selleys-...mover_p1232412
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  #9  
Old 17-01-2019, 01:46 PM
scoperboy (Stuart)
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Hacksaw blades were my first port of call, but everyone is missing the point that there is no gap...nothing fits except the thinnest wire.
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  #10  
Old 17-01-2019, 01:48 PM
scoperboy (Stuart)
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Quote:
Originally Posted by mswhin63 View Post
Try a thin stainless wire multi core and saw through the silicon. The multi strand may provide a cutting action where a single strand may not cut as well.
tried brass multistrand. It cuts well, but if you stop, it jams. It eventually snaps and then it jammed and in the way.
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  #11  
Old 17-01-2019, 01:50 PM
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DavidU (Dave)
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A guitar string .010" to .012" works wonders.
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  #12  
Old 17-01-2019, 01:59 PM
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Merlin66 (Ken)
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Good idea from Dave - Top E guitar string.....
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  #13  
Old 17-01-2019, 02:35 PM
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Ken ya got me mate, no ideas left.

Leon
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  #14  
Old 17-01-2019, 03:04 PM
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tempestwizz (Brian)
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There’s also dental floss you could try
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  #15  
Old 17-01-2019, 05:44 PM
Wavytone (Nick)
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Ah there is something as thin as dental floss but much stronger and will cut - the stainless steel multi strand wire used for control-line planes.

http://www.wightsmodelaircraft.com.au/flying-lines/

Be careful it will slice your fingers too.
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  #16  
Old 18-01-2019, 06:34 AM
JA
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You could try using a WIRE SAW< If you can find one thin enough. It's effectively teeth on a wire. Alternatively perhaps a coping saw blade. You could even grind it down in thickness to suit by mounting it on a timber block and perhaps using a belt sander and some skill.

Wire saw:
https://www.military1st.com.au/pd-pd...4aAmNbEALw_wcB

Coping saw:
https://www.totaltools.com.au/10134-...ping-saw-sj7cp

Best
JA
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  #17  
Old 18-01-2019, 10:55 AM
scoperboy (Stuart)
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Quote:
Originally Posted by DavidU View Post
A guitar string .010" to .012" works wonders.
Tried, as well as nylon fishing line. Heats up and snaps with little or no progress.
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  #18  
Old 18-01-2019, 11:44 AM
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mental4astro (Alexander)
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High tensile strength wire as Wavy mentioned.

Fishing line needs lubrication or it will bind from heat and snap. You could try using WD40 on the fishing line, but it most likely won't be strong enough.

You will need to make a jig though. The wire is anchored at one point on a board, the mirror/cell rests on a cushioned surface along its side, the other end of the wire is wrapped around a dowel. You then pull the dowel so wire slides under the mirror. This is the only way you will get the necessary leverage and force. Lubing the wire will help too. Make sense? Hopefully the diagram will help. You cannot pull the wire with your bare hands - it will cut you before the silicon.

An extra pair of hands is needed most likely too.

Alex
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  #19  
Old 18-01-2019, 11:51 AM
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mental4astro (Alexander)
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An alternate jig has the wire wound around two dowels, mirror fixed as below, and with a mate you cut through the silicon like sawing through a log, each taking turns pulling on the wire. This way will be faster and most likely safer for the mirror.
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  #20  
Old 18-01-2019, 06:56 PM
sharpiel (Les)
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If you're really stuck you could:

Use a bench or band saw to VERY carefully remove the wood through shaving the back off while holding the mirror upright. Then remove the glue with a chisel or scraper or razor. This could be dangerous if the saw binds in the wood and draws the mirror and/or your hands into the blade. Perhaps make a jig to hold the mirror vertical as it works against the saw.

Use the same jig with a hand saw instead to remove the wood. Much safer but the jig will need to be substantial to withstand the sawing.

Make a wooden jig to hold the mirror horizontal and use an electric plane or manual plane to shave the backing down to the glue/silicon. Then remove the glue with a chisel or scraper or razor.

Firmly fix the mirror and chisel the ply or wood away by hand.
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