Mirror Making Log
Randolph Center Sky Clock -


Here's a log of the time I've put into making my mirror so far.  I was amazed when I compiled it into one list.  It's a LOT of time!  If I was getting paid hourly to make the mirror, it would be very expensive. :-)

Date Hours Description
ALL 105.5 Total Working Time
4/19/06 2.5 Success!  If I've done my measurements correctly, I think so.  I worked on a little 1/3 center over center to try to settle the mirror down a little bit due to the high area in zones 4 & 5.  Only worked on it for about 10 minutes, then went  back to the tester.  Took me about 10 minutes to get set up, and found that the numbers were way off from what I expected.  .074 from bottom to top, which was more than the needed .067.  My hopes were crushed, but I decided to take 3 sets of measurements and then average them together to see what I got.  Similar results each time, and not looking good.  I decided to scratch it up to practice, and went back to FigureXP to plug in the numbers and see what I had.  Surprisingly enough, the figures showed that I had a fairly respectable mirror, but a little low in the center.  This isn't so bad, though, as   Overall, a 1/12.72 wavelength (.985 Strehl ratio).  I couldn't believe my eyes, so I plugged all the numbers into Foucault Test Analysis 2.0B, and it showed approximately the same value (1/11.6 and .9766 Strehl).  By then it was about 10:20pm, so I decided to see what I could do outdoors with it.  After about 45 minutes, I finally figured out what I was doing, and came up with a view of some stars, that actually focused to a point.  I then tried it on Jupiter, and although it was still extremely small, I could definitely see that it was round, and not a point.  I was utterly amazed.  I still don't think that I really believe that it could be true.  
The trick now, is to have Dave Kelley test it with the Stellafane tester with the flat mirror (Double Null Tester?) and see what he thinks.  I'm going to keep my fingers crossed.
4/16/06 1.5 3 turns of W's, tested, 3 more turns of W's, tested.  Unfortunately, my lap got a little dry on the last polish, and being a little overanxious at the progress, I tried working it a little bit.  Bad idea.  Wound up digging a good hole at about Zone 3.  Wasn't really sure what I was seeing, so I started sketching the measurements out on a sheet of paper, and then applied my measurements to the same sketch.  It shows I'm still high in Zones 5 & 4, but very low in Zone 3, and a little low in Zone 2, giving the effect that it's flat in the middle zones, then high walls to the upper level, or at least that's my best guess at this point.  Will have to ponder it some more, but I think I'm picturing it correctly here.
4/15/06 .5 A couple minutes of W strokes, about 7 times around the mirror.  Then tested.  Getting closer.  I'm about 1/2 way to a parabola.  Going well.
4/12/06 1.0 Started my W strokes tonight.  Spent about 5 minutes on the W's, going around the mirror about 5 times, then went down to the tester.  It's already starting to show a slight figure.  It looks like I'm about 25% of the way toward being a parabola.  Will need to go slow and easy on this.
4/9/06 2.0 About 1/2 hour more of slight W 1/3 Center over Center stroke, then spent some time setting up the tester.  Found it was time consuming to set it up each time, so I picked up a 1"x12"x10' so that I could build a stand for it with my sawhorses, in the basement.  It works well.  Couldn't find any figure in my mirror, so I've decided to try to figure it myself.  If it doesn't work, I've got time to go back to almost spherical before I go back to class #7.
3/30/06 1.5 Polished for a while using an almost 1/3 Center over center stroke (slight W 1/2" on each side of center.)  Heading back to almost a sphere, but don't need to quite go that far.
3/18/06 6.5 Mirror Class #6 - Telescope Building Lecture - Continued Figuring, and finished my mirror, just before I killed it.  I wound up bringing the mirror center down a little too low, with about 2 extra minutes of trying to make it a little bit better.  I have a little homework to do, and then 2-3 hours worth of work at the next class to finish it up.  Should be fine, and I should have a finished mirror to use this summer.
2/18/06 6.5 Mirror Class #5 - Foucault Testing Lecture (How to test for a parabola) - I had Dave Kelly test my mirror, and he found that it was a nice spherical shape all the way to the edge, with the exception of a slight high spot in the middle of the mirror.  He wasn't worried about this though, as the middle gets ground down slightly to make the parabola.  He started me in on the 'Classic W' stroke, which I must have done incorrectly as within about 5 minutes, I'd dug a hole in the middle of the mirror.  Remember that at this stage, a hole is a few 'millionths' of an inch deep.  So I went back to making it a sphere again.  It took about a half hour, and then I had  a decent sphere again.  I went back to work a little slower this time, and by the end of class, we'd started pushing it a little bit toward parabolic, but still with a long way to go, but still within the 'few millionths of an inch' range.
2/17/05 3.5 Decided to try pressing my pitch lap without warming it at all.  I had to press it for a little longer, but it worked very well.  I polished for well over 2 hours and then only needed a very slight retrim of the pitch facets, instead having to dig out new facets from pitch that had closed in, within about 45 minutes, like had been happening.  Now that I've seen how well it can work, it's easy to tell how to keep it that way.  Just a matter of being a beginner, and not knowing the difference.  It was a long lesson to learn, but one I'll never forget.  I was able to finish up tonight by doing another Ronchi test, which showed very straight lines, indicating that I'd finally reached a sphere, with no turned down edge.  I'll have to have it checked first thing tomorrow at class, though, in case I haven't checked it properly.
2/16/06 2.0 Trimmed my lap again tonight, then did some online research.  I think I've finally decided on the reason for my turned down edge.   My pitch lap is too soft.  This causes the pitch lap to polish the edges too much, while not polishing the center, since the pitch is just squishing out of the way in the middle.  Will try again some more tomorrow while trying a couple tricks to keep the pitch firmer, like not warming it as much before pressing, then letting it sit for a bit, and cold pressing it before I polish. 
2/15/06 2.0 Polishing (Turned Down Edge Removal)
After polishing, checked the figure using the Ronchi test.  This made me a little frustrated, as I didn't really see any difference from the Ronchi test that I did just before the last class.  Guess there's more work to do!
2/14/06 2.5 Polishing (Turned Down Edge Removal) 
If I'm seeing things correctly, it looks like the 'edge' is now only about 1/16" to 1/8".  Will have to work on it some more this week, as it needs to be spherical with no turned down edge by this weekend's class.
2/8/06 1.0 Polishing (Turned Down Edge Removal)
1/29/06 5.5 Mirror Class #4 - Figuring Basics Lecture - Re-Pitch  my pitch lap - Turned Down Edge removal instruction - Polishing out the turned down edge
Turned down edge is about 3/8" to 1/2" wide.  Dave and Ken are confident that it won't take too long to polish it back out, but both warn that it's going to take some work.
1/28/06 1.5 Polishing out & Re-trimming grooves in pitch
1/23/06 2.0 Polishing out & Re-t rimming grooves in pitch
1/20/06 1.5 Polishing out & Re-t rimming grooves in pitch
Still having some trouble with the edge.  It doesn't want to polish out.  Seems to be creeping closer, but going so slow.  I'll keep working it.  Can't take forever.
1/18/06 1.0 Polishing out
1/14/06 1.5 Polishing out & Re-t rimming grooves in pitch
1/9/06 2.0 Polishing out & Re-t rimming grooves in pitch
1/7/06 1.0 Polishing out
12/27/05 1.5 Trying out Foucault Testing
Overall looking good, but seems to have about a 3/4" turned down edge.  Did some research online, and the outlook doesn't look too promising.  It could take a while.  Some websites even recommend just masking out the edge, calling it a 6-1/2" mirror, and calling it polished out.  I don't want to do that, as I want an 8" mirror when I'm done.  I guess I'll just keep forging on and see if it goes away.
12/14/05 1.5 Polishing out & Re-t rimming grooves in pitch
12/11/05 2.0 Polishing out & Re-t rimming grooves in pitch
12/7/05 1.0 Polishing out
12/3/05 6.5 Mirror Class #3 - Polishing Lecture - Pouring Pitch Laps - Beginning Polishing
12/2/05 1.0 Fine Grinding - 5 micron
11/30/05 1.5 Fine Grinding - 12 micron AND re-polyurethaning my pitch lap base
11/27/05 1.0 Fine Grinding - 25 micron AND re-polyurethaning my pitch lap base
11/23/05 1.0 Fine Grinding - 25 micron AND  initially polyurethaning my pitch lap base
11/18/05 1.0 Fine Grinding - 40 micron
11/12/05 1.5 Fine Grinding - 40 micron
11/9/05 1.0 Grinding - 220 grit
11/5/05 7.5 Mirror Class #2 - Fine Grinding Lecture - Bad 120 Grit Show & Tell - Grinding - 220 grit
11/4/05 1.0 Grinding - 220 grit
11/2/05 1.0 Grinding - 220 grit
10/30/05 1.5 Grinding - 220 grit
10/29/05 0.5 Making Bad 120 Grit Samples
10/28/05 1.5 Grinding - 120 grit
10/26/05 0.5 Grinding - 120 grit
10/23/05 1.0 Grinding - 120 grit
10/22/05 1.5 Grinding - 120 grit
10/19/05 1.5 Grinding - 120 grit
10/16/05 1.0 Grinding - 120 grit
10/15/05 2.0 Grinding - 120 grit
10/12/05 2.0 Grinding - 120 grit
10/9/05 1.0 Grinding - 120 grit
10/8/05 1.0 Grinding - 120 grit
10/5/05 1.5 Grinding - 80 grit
10/2/05 1.5 Grinding - 80 grit
10/1/05 7.5 Mirror Class #1 - Grinding Lecture - Edge Beveling - Grinding - 60 grit




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Site was last updated on: 04/20/2006