Julie's Mirror Log
Randolph Center Sky Clock -


Julie is making a 4-1/8" f/6 mirror.  It's going well.

Here's a log of the time Julie has put into making her mirror so far.  

Date Hours Description
ALL 91:00 Total Working Time
11/22/07 2:00 Beveling & 80 grit hogging.
11/24/07 4:00 Beveling & 80 grit hogging
11/25/07 0:50 Beveling & 120 grit fine grinding  (Bad Grit.  Left pits bigger than 120 grit.  Need to get rid of it before using again.)
11/25/07 2:10 Beveling & 220 grit fine grinding
11/26/07 1:30 220 grit fine grinding
11/26/07 0:25 Beveling & 40 micron fine grinding  -  It's coming out closer to f/4.  It's a little faster than I was planning, but I think I'll go with it at this point.
11/30/07 1:15 40 micron fine grinding
11/30/07 1:20 25 micron fine grinding  -  Almost finished fine grinding!
12/01/07 1:15 12 micron fine grinding  -  Sooo Close!
12/01/07 1:30 5 micron fine grinding   All done fine grinding!  Now to make a pitch lap and start with polishing!
12/08/07 6:00 Mirror Class 3 - My first! - (Polishing Lecture) - Started off with a quick test by John Martin of the focal length.  Turns out we were off by a power of two on the calculations, and I've actually got an f/2 instead of an f/4 mirror.  That's way too fast for me, so I think I'll try to bring it back to the f/6 range I was originally planning.
Started out grinding, then stopped for the polishing lecture, then back to grinding. 
Stopped part way through the day to make my patch lap.  I'm using the same tool that Samantha used on her 4-1/4" mirror, but the pitch has been removed, and it's ready to pour a fresh coat.  The tools ready to go, and just waiting for fine grinding to finish again.
12/9/07 1:30 220 grit fine grinding
12/10/07 2:45 220 grit fine grinding
12/14/07 2:15 120 grit fine grinding
12/16/07 3:00 120/220 grit fine grinding - Finally back to where I'm happy with it, although it took a while.  It's looking more like it's about an f/7.5, but that's ok.  A little easier to get magnification with a bigger eyepiece, and a good contrast to Samantha's f/3.88.  About half way through with the 220 grit.  That should finish up quickly.
12/17/07 1:30 220 grit/40 micron fine grinding - done with 40 micron
12/19/07 1:00 25 micron fine grinding
12/20/07 1:30 12 micron/5 micron fine grinding - All done fine grinding! (Again!)
12/27/07 1:30 Polishing
12/29/07 2:00 Polishing
1/2/08 2:00 Polishing
1/4/08 1:15 Polishing - It's all polished out.  I'll find out from Dave Kelly on Sunday how it looks.
1/6/08 6:00 Mirror Class 4 (Figuring Lecture) - Started out warming and pressing, then attended the figuring lecture.  Afterwards, had Dave Kelly test my mirror, and he said that it's polished out well, but has a very deep zone in the center.  A super deep hyperbola.  Focal length difference was about .75" to .8", so it's extremely deep.  (Total correction for my mirror should be about .020".)  Dave suggested pressing a small piece of paper between the mirror and the lap, so that the center of the lap was lower, and would allow for polishing in the outer zones, without continuing to push down the center.  Polished this way through the day, and had brought it back to around .675".  Homework is to get rid of the hole.
1/19/08 1:30 Polishing - Changed from a piece of paper to a piece of overhead transparency shaped like a circle, about 2/3 the diameter of the mirror.  This will help as the paper keeps deteriorating. - Still ~ .600" to go.
1/20/08 1:30 Polishing & Testing for spherical - Still ~ .525" to go.
1/25/08 2:00 Polishing & Testing for spherical - Still ~ .450" to go.
2/1/08 3:00 Polishing & Testing for spherical - Still ~ .350" to go.
2/2/08 1:30 Polishing & Testing for spherical - Still ~ .275" to go.
2/4/08 2:45 Polishing & Testing for spherical - Still ~ .150" to go.
2/8/08 3:15 Polishing & Testing for spherical - getting spherical, but with an odd figure.  Will talk to Dave about this tomorrow.
2/9/08 6:00 Mirror Class 5 (Testing Lecture) - Pressed while attending the lecture.  Afterwards, had Dave Kelly test my mirror, and he said that it's looking much, much better, but has a raised ring around the outer zones.  He suggested taking the transparency circle, and trimming it like a star, and continue with the pressing using it.  Polished this way for a while, and by the end of the day, Dave said that I had improved a lot.  Homework is to continue doing this, until the zone is gone, then do center over center to smooth everything back out.
2/16/08 2:30 Polishing & Testing for spherical
2/17/08 1:30 Polishing & Testing for spherical
2/22/08 3:00 Polishing & Testing for spherical
2/23/08 1:45 Polishing & Testing for spherical
2/28/08 1:30 Polishing & Testing for spherical
3/8/08 1:30 Mirror Class 6 (Constructing a Telescope Lecture) - Missed this class due to freezing rain, but decided to work on my scope a little anyway.  - Polishing & Testing for spherical
3/22/08 1:45 Polishing & Testing for spherical
4/5/08 6:00 Mirror Class 7 (Final Class) - Pressed for a while, then had Dave Kelly test to see how things looked.  He was very impressed with the improvement of the mirror, but said that it still has a touch of a turned down edge, left over from the outer raised ring.  Keep pressing with the star, don't worry about the center raising up, and polish the edge out before doing anything else.  By the end of class, it was looking much better, but the TDE was still slightly there. I am getting a central hill like Dave had mentioned, but will ignore it for now.  Homework - Finish working out the edge, then attack the central hill with a 1/3 to 1/2 Center over Center stroke.  Call him when finished, and he'll bring his tester to the next Stellafane meeting, and check it out. 
4/14/08 2:00 Polishing & Testing the TDE.  It's almost gone.  Another couple hours, and I should have a good edge again.




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Site was last updated on: 04/23/2008