Progress on 8" mirror

[dValve]

Hi Joe,

I've just sent a rather long private message to you regarding your friend Albert, which I hope will be helpful. I drove my wife and son to the hospital this morning; he begins chemo on Wednesday. I hope and pray that he tolerates it well.

On the mirror-making front, I checked my mirror again, and after about 3 1/2 hours of work, I still have a smooth sphere, and am starting to see a diffraction ring. I also still see some turned down edge, so I will continue to work mostly MOT with 1/4 strokes. The heat is causing my channels to close prematurely, which is slowing down my progress. It's tempting to make a harder pitch lap, but I fear that the weather will change as soon as I do. I just rechannel more often for the present. I'm also making an extra wide bevel at the edge of my lap, to reduce the danger of TDE. I'm guessing another two or three hours of work should finally bring me to the point where I can take my first crack at parabolizing, but I may not have enough time this week to get there.

[astrodandare]

Hey guy,s.
you have my greatest sympathy in this time of illness. Had my fair share of the stuff and it sure ain,t nice .but hoping and praying 100% you all pull through . watching Dan

[BABOafrica]

I read your last report with great interest, both about your son and your progress on the mirror. Life is complicated!!!

Let us know who all this works out.

Clears,
Joe

[dValve]

It's been a tough week. My son had a weird reaction to the first night of chemo; he started shaking violently and his fever spiked. It looked to the nurses like sepsis, so they put him on an antibiotic. Very frightening. But his white blood cell count turned out to be normal, and his fever has been stable since. On the positive side, he's had very little nausea, and ate a full dinner last night. He'll be coming home this evening. Next week he has outpatient chemo, then a three weeks off. It will be nice for us all to be home.

I've left my lap out most of the week, thinking that the work would be soothing, but I've spent most of my free time at the hospital. I'll take the lap out of the fridge tonight, and rechannel tomorrow.

I wrestled with TDE on my last mirror; it took forever to remove at the time, but I'm pretty sure it's because my lap was too hard. I'm seeing much steadier progress now with each work session, so I'm hopeful that I may have it licked by sometime next week.

[BABOafrica]

Good news about your son! And good luck with that mirror.

Clears,
Joe

[dValve]

My son has been doing pretty well, although his energy is low. I'm now able to think about doing more work on my mirror.

My lap sat out all week, and when I looked at it on Saturday, it had begun to deform. I did a hot press, then rechanneled. After about an hour and a half of work, the circle pattern that I had previously seen in my mirror seems to be returning. This seems to happen whenever I work MOT. The edge still looks turned, both on the Ronchi and the Foucault tests. Ironically, I see a diffraction ring. My current theory is that the too warm pitch is changing shape too readily. After 20 minutes I feel a small skip as I pull the mirror toward me. I've been cold pressing nearly every twenty minutes, probably a good practice in any case. I may need to wait until the weather cools by a few degrees before I can make much progress. Fortunately, next week's forecast calls for temperatures in the low 80's, a welcome break. And today's thunder showers may cool my house enough to do some work this evening. I will also try to use narrow V and W strokes.

[dValve]

If I may go off topic for a second (as if I haven't already), Joe, what do the 2012 M40, M70, M80 Sketch Award banners mean that appear when you post?

[sopticals]

My son has been doing pretty well, although his energy is low. I'm now able to think about doing more work on my mirror.

After 20 minutes I feel a small skip as I pull the mirror toward me. I've been cold pressing nearly every twenty minutes, probably a good practice in any case.

Hi Dan(dValve),

Sorry to hear your going through such a difficult time with your boy.

If I were you I would be limiting my figuring sessions to 8-10mins max and cold pressing before attempting a furthering figuring session. When laps begin to "skip" or move erratically the figure of revolution will suffer with zones, hills/hollows, and worse, astigmatism can rear its ugly head. When a lap is doing its best work it will move smoothly and uniformly over all diamaters of the mirror. At the slightest hint of grabbing/skipping or non-uniform movement over all diameters, STOP, repress lap.

[BABOafrica]

If I may go off topic for a second (as if I haven't already), Joe, what do the 2012 M40, M70, M80 Sketch Award banners mean that appear when you post?

There are two different programs in the ASTRONOMY FORUM section. I signed up for both.

One is simply sighting all the Messier objects. (I got the certificate for 70 and I've got one more Messier object to site in order to get the certificate for the 110 objects.)

The second is for sketching. (I got the certificate for 80 and I've got six more Messier objects to sketch in order to get the certificate for the 110 objects.)

It's really a neat program. Check it out in the ASTRONOMY FORUM section

Clears,
Joe

[dValve]

Thanks for the info on the Messier program, Joe. I looked at the forum page, but didn't see how to sign up. Is it posted on a specific thread?

The good news is, my son is home, and seems better than I've seen him in a long while. He has a one week break from treatment. And the weather is cooling, which has made it possible to get back to work on my mirror.

After a productive day Saturday, I found that I'd made good progress. My mirror was almost perfectly spherical again! I did some long W MOT parabolizing strokes and some normal W strokes TOT. This seems to work well for repairing oblateness, as this is how I got spherical the first time. But my edge is still slightly turned down. I could probably blacken the outer 1/8" and be done with it, but I fear that if I proceed with parabolizing, I may turn the edge even more.

And here's my dilemma: whenever I do short strokes MOT to fix the TDE, I end up oblate. I can fix it with some parabolizing strokes and some normal TOT W strokes, but the first time I did this I turned the edge in the first place! So the fix for one problem causes the other, and visa versa!

After some research online, I'm going to try a suggested posted by Mike Lockwood. He's written some very useful posts on mirror-making, particularly "Mike's Mirror Making Musings" (http://www.loptics.com/ATM/mirror_ma.../full_lap.html). He has also posted an interesting theory regarding turned down edge and oblate figures, which he believes are related (http://www.loptics.com/ATM/mirror_ma...te/oblate.html). I may try his technique once I've rechanneled my lap (which I hope to do tonight).