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  #121  
Old 30-06-2018, 05:12 PM
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Lognic04 (Logan)
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I'm having issues with 12micron - it is EXTREMELY sticky, like, hard to move! What is the issue here?!
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  #122  
Old 30-06-2018, 06:28 PM
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Quote:
Originally Posted by Lognic04 View Post
I'm having issues with 12micron - it is EXTREMELY sticky, like, hard to move! What is the issue here?!
It sounds like you are adding too much grit and not enough water. It should be quite runny, the consistency of water. Try mixing it up in a squeeze bottle - eg old shampoo bottle and add a dash of detergent. Squirt it on the mirror and then lightly run your clean fingers through it to check for sharp bits.

If you look at the start of this video, you'll see how runny it is:

https://m.youtube.com/watch?v=noBWSeozpkI

A fine grinding wet should last 5 minutes or more.

Rod
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  #123  
Old 30-06-2018, 06:51 PM
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Thanks Rod, that fixed it!
However, it still loves to hug one particular edge region. Any ideas as to why this occurs?
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  #124  
Old 30-06-2018, 07:30 PM
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It may be drying out in that area. Add a little more of the mixture and see if that helps. Donít force it when grinding. Be gentle.

Rod
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  #125  
Old 30-06-2018, 07:36 PM
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It is like that from the start however?
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  #126  
Old 30-06-2018, 07:43 PM
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Maybe do a sharpie test just to make sure the tool and mirror are well matched. Use a felt tip pen.
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  #127  
Old 30-06-2018, 07:50 PM
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Also try adding a little more grit to the mixture
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  #128  
Old 01-07-2018, 12:02 PM
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I feel it might be best to skip directly to polishing at this stage as I am having sticking issues. I will use polishing pads so the time spent will be marginally different from 12 to 5 micron. Should I skip?
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  #129  
Old 01-07-2018, 03:05 PM
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Hi Logan

I don't like the idea of jumping to polishing before we know what's going on. You will be polishing for a long time, even with pads and if you have a problem where the mirror and tool are not spherical it just wastes time. I would prefer to at least finish with 9 micron and preferably 5.

I would really like to be sure your mirror and tool are properly mated. That's why I suggest the sharpie test as described on the stellafane site.

My other theory is that you may have now added too little aluminium oxide to the water. That would cause it to grab. Make the mixture a little richer and see if that changes things.

Perhaps you could post a video of what you are doing somewhere. That might make it easier to spot the problem.

Rod.
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  #130  
Old 01-07-2018, 03:11 PM
Billyboy78 (Bill)
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If you have sufficient lube, as in watery grit, then the only reason they will stick is that the discs aren't matched up perfectly from rough grinding. Possibly they match up COC and thus you get a good sharpie test, but trying to move off centre air can't get in as they mis-match and a vacuum is formed locking everything up.

You have 3 options, go back to 25 micron and grind slowly and carefully aiming for 100% match, persevere with 12 micron, it will eventually come good, or put a flash polish on the mirror and do a KE test to see where you're at.
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  #131  
Old 01-07-2018, 03:16 PM
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Maybe I could try channelling the tool? It has absolutely no gaps so that could be a problem. I will also add grit, see if this continues and if it does post a video
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  #132  
Old 01-07-2018, 04:29 PM
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Hi Logan

Don't try channeling the tool at this point. It's only going to invite scratches. Plenty of people make telescope mirrors with a glass blank as the tool - no channels.

Remember to try the easiest solutions first. Vary the mix a bit as discussed. See if that helps. Try a sharpie test. It's easy to do.

When you have done the above report back and then we can discuss what to do or try next.

Rod
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  #133  
Old 05-07-2018, 04:35 PM
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About to shellac and begin polishing! Yes only after 12u, as Mark (from ASV) said that it would be best. By the way, the sticking is pretty much gone after letting it sit for a few days and i presume thermally equalise.
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  #134  
Old 05-07-2018, 08:10 PM
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Polishing pads on! And so begins the 3rd and final part of mirror making!
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  #135  
Old 07-07-2018, 03:32 PM
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Polishing is going well!
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  #136  
Old 19-07-2018, 01:52 PM
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Forgot Stefan was watching this!!!
Did polishing with the pads for 6 or so hours and I realised fine grinding wasn't done, so I went back to 12,9,5 and then begin polishing again, by the way, I am 2hr 20 mins in and have already a beautiful shine across the entire mirror and the edge is near invisible! If I am not pouring the lap at the asv i will be finishing Polishing on the awesome spinny machine
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  #137  
Old 20-07-2018, 09:35 AM
Stefan Buda
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I give you another 6 weeks before I re-join the race.


You may not realize that you are only about half way trough this job. By far the hardest part is still ahead of you.
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  #138  
Old 30-07-2018, 08:04 AM
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29 jul
begin figuring
1hr COC to reduce ring

1hr blending, ring nearly gone, bad tde

diagnosis tot short strokes

20min tde tot edge improved, slightly oblate
diagnosis mot tde strokes

Just chucking my log here.
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