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  #41  
Old 11-10-2018, 10:28 AM
Billyboy78 (Bill)
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Quote:
Originally Posted by Lognic04 View Post
Should i channel my tool?
Yes, just use a ordinary saw or hacksaw, and a single cut will do it. It will only take a minute.
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  #42  
Old 11-10-2018, 10:32 AM
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Lognic04 (Logan)
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Ok cool. the gaps between my tiles are too thin for a hacksaw though? (i didnt plan on channeling)
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  #43  
Old 11-10-2018, 05:26 PM
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Ok so I did the sharpie test at 25u and it is perfect contact (even dimming). I think it must have just been the channels, I dug new ones out with my fingernail.
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  #44  
Old 11-10-2018, 07:38 PM
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Did 35mins, total 1hr50m. 25u is done!
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  #45  
Old 13-10-2018, 12:26 PM
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Hmm, FL wandered to 48cm over the course of 25u - should I do anything?
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  #46  
Old 13-10-2018, 02:49 PM
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F2.8 with a 20 mm eyepiece gives 21x. F3.2 with a 20 mm eyepiece gives 24x.

The field with a 100 degree eyepiece at 21x will be roughly 4.76 degrees. The field with same eyepiece at 24x will be about 4.16. So you lose 0.6 degrees by staying at F3.2. Personally I think a 4 degree field is huge so I would leave it at F3.2. It will be a little easier to figure too.

Rod
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  #47  
Old 15-10-2018, 11:23 AM
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Started 9 micron grinding. Have done 15 mins so far, no rush because i'm picking up the polishing stuff on the weekend
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  #48  
Old 22-10-2018, 12:02 PM
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You better start building one of these☺https://youtu.be/75AoWl3jhcQ
Alex
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  #49  
Old 22-10-2018, 02:20 PM
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Wow, thats pretty spectacular!!
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  #50  
Old 23-10-2018, 06:53 PM
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Alright - finished 9u and therefore fine grinding!!!
Pouring the lap tomorrow and going to make a video
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  #51  
Old 25-10-2018, 08:13 AM
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Ok, lap is poured! Gotta sort out some contact issues after school.
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  #52  
Old 01-11-2018, 01:25 PM
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Polishing is going well, 2 hours done now but center has maybe 15% more to go and edge 40% as a rough guess? I am working mot. Also my channels are closing fast (soft acculap), which means channeling,which means pitch getting thinner, and now the pitch is id estimate 6 or 7mm thick? I think this lap will get me polished out but not into figuring. Unless i somehow pour new pitch onto the lap?
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  #53  
Old 06-11-2018, 10:58 AM
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Mirror is polished out after 4 hours!
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  #54  
Old 06-11-2018, 12:09 PM
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In my experience....
Just double, triple check the outer edges for minor small remaining pits Bright light and loupe eyepiece...
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  #55  
Old 08-11-2018, 09:59 AM
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Figuring has started, edge is just flat and im having a hard time with mike lockwood's reccomended strokes (not doing much to correct the edge!)
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  #56  
Old 11-11-2018, 06:33 PM
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How do you guys go about fixing kinks?
I need to fix this one:
https://cdn.discordapp.com/attachmen...2/IMG_1217.jpg
https://cdn.discordapp.com/attachmen...6/IMG_1211.jpg
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  #57  
Old 12-11-2018, 07:09 PM
sfarndell (Scott)
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Hi Logan

My experience is more with larger mirrors (18" f4), where you work with sub-diameter laps, so I'll share what I know:

More information is needed:
1. Have you polished enough? 4 hours is relatively short if polishing by hand.

2. Are you inside / outside focus? If you're inside focus, then you have some issues (use short strokes with small overhang slightly off-centre to lower the centre)

3. If you're outside focus, then it's not so much as a kink, but a spherical centre and some parabolisation towards from the 70% zone and you don't seem to have a TDE, which is good news! F2.8 is a pretty aggressive / short focal ratio. Check mel-bartels' website for the matching ronchigram to determine if you've over-parabolised the edge. If not, all you need to do is use a subdiameter lap (4") and parabolise the centre (short chordal strokes with minimal overhang close to COC), then smooth with full size lap.

Last edited by sfarndell; 12-11-2018 at 07:22 PM. Reason: Inside / outside focus advice was muddled
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  #58  
Old 12-11-2018, 07:20 PM
sfarndell (Scott)
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entered your details here https://www.bbastrodesigns.com/ronchi.html

You'd also need to tell us what your Rochi LPI are. I assumed 4 per mm, ROC of 840mm. Using this you seem to have an over-parabolised edge. I'd return to a sphere using the full-size lap with a 1/3 D stroke, offset from centre. Likely you still need to polish out the mirror anyway so this shouldn't take too long.
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  #59  
Old 18-11-2018, 11:15 AM
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Hi Scott,
Sorry for not replying earlier!
I now need to add parabolization to the 0.7 zone according to Bratislav, he says either full size scrubbing 0.7 down, or a subdiameter.
I'm waiting for my mentor to reply on cloudynights though.
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  #60  
Old 21-12-2018, 01:34 PM
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So I had to return to sphere, and have been fixing a tde for the month. I only need about 1 more hour to fix it though! Woo!
Rod helped me make the beautiful wooden birch octagonal tube, it looks great! Now it needs a coat of polyurethane
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