Polishing Log

Polishing Log - Don's 12.5" F/4.5 Mirror

Links: Don & Becky Home Page, New Scope Page

I ordered a thin (1.5" thick) Pyrex mirror kit from Newport Glass Works. The mirror and tool came rough ground.

24 Oct 2001	The tool has an estimated 111.5" radius of curvature (ROC) and the mirror estimated 112.0".
29 Oct 2001	Ground mirror with 220 grit, Tool On Top (TOT) for ~1 hour.
30 Oct 2001	Ground mirror with 220 grit, TOT, ~1 hour. Finished 220 grit.
2 Nov 2001	Ground mirror with 30 grit, TOT, ~1 hour.
3 Nov 2001	Ground mirror with 30 grit, TOT, ~1 hour. Ground mirror with 15 grit, TOT, ~2 hours. Ground mirror with 20 grit, Mirror On Top (MOT), ~2 hours.
5 Nov 2001	Ground mirror with 15 grit, MOT and TOT, ~2 hours.
7 Nov 2001	Ground mirror with 9 grit, MOT and TOT, ~1 hour.
9 Nov 2001	Ground mirror with 9 grit, MOT and TOT, ~1 hour. sagattia 0.0538.
10 Nov 2001	Poured lap at TM workshop. Gugolz 64 pitch.
11 Nov 2001	Channeled the pitch with a soldering iron.
12 Nov 2001	Cold pressed MOT with net between mirror and tool. ~10 pounds weight, ~20 minutes. Worked mirror, MOT, moderate pressure, ~15 minutes. Cold pressed MOT with net, ~10 pounds, ~40 minutes. Worked mirror, MOT, moderate pressure, ~30 minutes.
13 Nov 2001	Cold pressed with net, ~10 pounds weight, ~1 hour. Worked mirror, MOT moderate pressure, ~25 minutes. First check with Ronchi looks good, ~113" ROC measured.
14 Nov 2001	Cold pressed with net, ~10 pounds weight, ~90 minutes. Worked mirror, MOT moderate pressure, ~15 minutes.
15 Nov 2001	Cold press with net, ~10 pounds weight, ~20 minutes. Worked mirror, MOT light pressure, ~15 minutes. Cold press ~ 20 minutes. Worked mirror 15 minutes. Cold press ~ 20 minutes. Worked mirror 15 minutes. Cold press ~ 20 minutes. Worked mirror 15 minutes. Cold press ~ 20 minutes. Worked mirror 15 minutes.
16 Nov 2001	Used brass wire brush to brush the lap gently. Cold press with net, ~10 pounds, 20 minutes. Worked mirror, MOT, moderate pressure, short strokes over center, 30 minutes. Cold press with net, ~10 pounds, 20 minutes. Worked mirror ~30 minutes Rechanneled lap.
17 Nov 2001	Cold press with net, ~10 pounds, 45 minutes. Worked mirror, MOT, 7 lbs. wt., short strokes over center, 30 min. See weight on mirror in photo. Ronchi - good edge, mirror a little concave, 113 ROC. Brass brush lap, light pressure. Cold press with net, ~15 lbs. wt., ~ 15 min. Worked mirror, MOT, 7 lbs., 30 min. Cold press with net, ~15 lbs. wt., ~ 15 min. Worked mirror, MOT, 7 lbs., 30 min. Cold press with net, ~15 lbs. wt., ~ 15 min. Worked mirror, MOT, 7 lbs., 30 min. Ronchi - good edge but center slightly MORE concave.
23 Nov 2001	Cold press with net, no weight, 6 days results in good micro- channeling shown at right. Work mirror, TOT, 7 lbs., shallow "W" pattern, 30 min. Very squeaky during working Resulted in turned edge. No press between working. Work mirror, MOT, 7 lbs., STRICTLY short strokes over center, 30 min. Turned edge a little better. No press between working. Work mirror, MOT, etc... 30 min. (Inside ROC) Looks MUCH better. see at right. Cold press w/o net, 60 minutes. Work mirror, MOT, 7 lbs., strictly short strokes over center, 30 min. Good edge but a little concave.
24 Nov 2001	Cold press with net, ~24 hours. Work mirror, TOT, 7 lbs., strict over center, 25 min. Ronchi looks quite good.
25 Nov 2001	Cold press with net, ~ 18 hours. Work mirror, TOT, 7 lbs., strict over center, 30 min. Cold press no net, 7 lbs., ~2 hours. Work mirror, TOT, 7lbs., strict over center, 35 min. Ronchi looks quite good but very slight turned edge.
26 Nov 2001	Cold press with net, ~24 hours. Work mirror, MOT, 7 lbs., strict over center, 30 min.
27 Nov 2001	Cold press with net, ~24 hours. Work mirror, MOT, 7 lbs., strict over center, 30 min. Cold press ~15 minutes. Work mirror, TOT, 7 lbs., short over center, ~30 min. Very squeaky. Ronchi, good edge, very, very slight concave.
30 Nov 2001	Cold press with net, ~48 hours. Work mirror, TOT, 7 lbs., short over center, 30 min. Cold press, no net, 7 lbs., ~90 min. Work mirror, TOT, 7 lbs., 15 min., squeaky Work mirror, MOT, 7 lbs., 15 min., squeaky Ronchi shows some distortion (Inside ROC).
1 Dec 2001	Cold press 90 min. Work MOT, 7 lbs., new cerium oxide (from Jim), 30 min. Ronchi looks good Cold press, 7lbs., 90 min. Work MOT, 7 lbs., 30 min.
2 Dec 2001	Cold press w/net, 7 lbs., 19 hours Work MOT, 7 lbs., 25 min. Ronchi slightly concave Cold press, 7 lbs., 15 min. Work TOT, 7 lbs., 15 min. Resistance irregular so stopped working Ronchi ok
3 Dec 2001	Cold press, 7 lbs., 20 min. Work MOT, 7 lbs., 30 min. Squeaky Ronchi looks good
4 Dec 2001	Cold press, no weight, with net, 24 hours. Work MOT, no weight, 10 min. Mirror was "sticky" so worked without the 7 lbs. weight. Work MOT, 7 lbs., 20 min. Ronchi looks good.
5 Dec 2001	Cold press, 7 lbs., 2 hours. Work MOT, 7 lbs., 20 minutes. Squeaky. Ronchi (inside ROC). Looks good after 880 minutes of polishing.
7 Dec 2001	Cold press, 7 lbs., 40 min. Work, MOT, 7 lbs., 20 min., squeaky Ronchi looks very good inside and outside ROC.
8 Dec 2001	Cold press, 7 hours, no weight. Work, MOT, 7 lbs., parabolizing stroke, 1 time around Ronchi shows VERY slight concave, almost nothing
9 Dec 2001	Cold press ~ 2 hours Very thin cerium oxide Work, MOT, 7 lbs., parabolizing stroke, 2 times around Ronchi shows almost no change - cool garage
14 Dec 2001	Cold press in kitchen ~ 45 min., ~65 F degrees Work, MOT, 2 "W" strokes, 1 time around parabolizing Ronchi slight hole, distortion due to convection currents
16 Dec 2001	Cold press in kitchen ~90 min., ~70 F degrees Work, MOT, 7 lbs., short stroke over center Ronchi, center hole removed Cold press in kitchen ~90 min., ~70 F degrees Work MOT, no weight, short stroke over center
1 Jan 2002	Cold press in garage (cold), 7 lbs., ~ 3 hrs. Work, MOT, no wt., 15 min., short over center to give fine surface. Ronchi good inside ROC. Outside ROC opposite of parab. Cold press, cold garage, 7 lbs., 40 min. Work, MOT, 7 lbs., med. & short over center, 15 min. Ronchi, good sphere inside and outside.
5 Jan 2002	Cold press, in house (warm), 7 lbs., 90 min. Work, MOT, 7 lbs., parabolize, large "W", 1 X around. Cold press, in house, 7 lbs., 30 min. Work, MOT, 7 lbs., parab. stroke large "W", 1 X Ronchi almost no difference. Maybe a little parabolized Maybe a little hole.
6 Jan 2002	Cold press, in house (warm), 7 lbs., 60 min. Work, MOT, no wt., open "W", mirror center 6" from edge of tool, almost no impact Cold press, garage, 7 lbs., 60 min. Work, MOT, short strokes over center, return to sphere Warm Press, 7 lbs., ~ 30 min. Work, MOT, not wt., open "W", mirror center 3" from edge of tool Ronchi shows hole. Lap must be too firm. According to Edmund's "All About Telescopes," if the lap is too firm, the parabolizing stroke will put a hole in the center of the mirror. It certainly does. Cold press, 7 lbs., in garage (cool), 30 min. Work, MOT, 7 lbs., short over center, 15 min. Ronchi is better but still a hole Cold press, 7 lbs., in garage, 2 hrs. Work, MOT, 7 lbs., short over center, 30 min. Ronchi quite a bit better but hole not completely removed.
13 Jan 2002	Cold press, 7 lbs., in garage (cool), 90 min. Work, MOT, no weight, short over center, 15 min. Surface feels uneven, so removed weight. Added weight when felt even. Work, MOT, 7 lbs., short over center, 15 min. Ronchi: opposite of parab., slight hole remains
14 Jan 2002	Cold press, 7 lbs., room temp, 2 hours Work, MOT, 7 lbs., VERY short over center, 15 min. Surface feels even Work, MOT, 7 lbs., med. strokes over center, 10 min. Ronchi: opposite of parab., slight hole remains
19 Jan 2002	The goal is to get the mirror back to a sphere. Mirror on Top working does not seem to be helping, so I'm changing to TOT. Cold press, 40 min., 7 lbs., in the COLD garage Work, TOT, 7 lbs., 10 min., short narrow W stroke, +/- 1" (lateral) from staying over center. Feels very uneven during working. Ronchi: The hole is reduced. Positive progress. Cold press, 1 hr., 7 lbs. in garage Work, TOT, 1 time around, 7 lbs., short narrow W stroke, +/- 1" (lateral) from staying over center Ronchi: Turned edge.
20 Jan 2002	I brushed the lap with a brass brush. Cold press, 7 lbs., COLD in garage, 4 hours. Work, TOT, 2X around, short over center. Ronchi: The turned edge seems a little worse. I need a change in process. I'm going to apply more pressure, and use slower strokes. Cold press, 7 lbs., 2 hrs. cold press Work, MOT, 7 lbs., 2X around, firm, deliberate, slow strokes over center, shallow (side to side) W pattern. Ronchi: Hole in center is disappearing, turned edge remains.
21 Jan 2002	Cold press, 7 lbs., 40 min. Work, MOT, 7 lbs., 3X around, firm, deliberate, slow strokes over center, shallow (side to side) W pattern. Ronchi: Closer to a sphere but turned edge still there.
4 Feb 2002	Cold press, 7 lbs., 90 min. cold Work, MOT, 7 lbs., firm pressure, short over center, 30 min. Ronchi: Closer to sphere, turned edge still exists.
5 Feb 2002	Cold press, 7 lbs., 2 hrs. Work, MOT, 7 lbs., firm pressure, short over center, 10 min. Surface feels uneven. Use hair dryer to warm lap 5 min. Work, MOT, 7 lbs., firm pressure, 15 min. Feels more even.
6 Feb 2002	Cold press, 7 lbs., 90 min., cold Work, MOT, 7 lbs., firm pressure, short over center, 10 min. Ronchi: Turned edge improved. Closer to sphere.
16 Feb 2002	Brought barrel into house (warmer) Cold press, 7 lbs., 1 hr. Work, MOT, 7 lbs., short over center, 23 min. Ronchi: Looks quite good, edge still turned.
17 Feb 2002	Cold press, w/net, 24 hrs., nice net pattern Work, MOT, 7 lbs., short over center, 20 min. Ronchi: Turned edge much better. Soaked mirror & lap in 90 F water ~5 min. each Press, 7 lbs., 15 min. Work, MOT, no weight, short strokes STRICTLY over center 5 minutes. Ronchi: Turned edge is mostly gone Very slightly off sphere Soaked mirror and lap 90+ F, press 7 lbs., Work, MOT, 3X around, no weight, STRICTLY over center Ronchi: Center looks better, slight turned edge. Cold press, no weight, 30 min. Work, MOT, no weight, short over center, 10 min. Ronchi: Edge looks pretty good. Surface opposite of parabola. Soaked mirror and lap warm water Press 7 lbs., 30 min. Work, MOT, no weight, medium parabolizing stroke, "W" stroke twice over and back, 1X around Ronchi: No apparent change Soaked mirror and lap in warm water Press 7 lbs., 20 min. Work, MOT, 7 lbs., 1X around, medium parabolizing stroke Ronchi: Edge look pretty good, closer to sphere
19 Feb 2002	Warm press, no weight, 20 min. Let cerium oxide water solution settle and skimmed solution Work, MOT, 7 lbs., medium parabolizing stroke, 1X Ronchi: No apparent change. Press, 7 lbs, 20 minutes. Work, MOT, 7 lbs., medium prabolizing stroke, 1X Work, MOT, no weight, deep parabolizing stroke, 1X Ronchi: No apparent change
20 Feb 2002	Press, 7 lbs., ~60 min. Work, MOT, no weight, deep parabolizing stroke, 2X Ronchi: Good edge, close to sphere, almost no change
21 Feb 2002	Press, 7 lbs., 15 min. Work, push-pull, parabolize with deep strokes, 2X Ronchi: Very slightly parabolized Press, 7 lbs., 15 min. Work, MOT, push-pull, deep parabolizing stroke, 2X Ronchi: no change
23 Feb 2002	Rechanneled lap, brushed with brass brush, two directions Press, 7 lbs., 50 min. Work, MOT, deep parabolizing stroke, 2X, feels good Ronchi: Parabolizing, but slight hole in center Press, 7 lbs., 15 min. Work, MOT, thin cerium, medium parabolizing, 2X Ronchi: Hole almost gone, slight parabolized medium stroke works better than deep stroke Press, 7 lbs., 20 min. Work, MOT, 7 lbs., medium parabolizing stroke, 1X Ronchi: Step backwards. Don't use the weight. Appears that weight causes lap to flow. Press, 7 lbs., 20 min. Work, MOT, no weight, medium parabolizing, 2X Ronchi: Looks good, moving in right direction Press, 7 lbs., 20 min. Work, MOT, long parabolizing stroke, 1X Ronchi: Closer to sphere Appears that long strokes cause lap to flow. Press, 7 lbs., 20 min. Work, MOT, NARROW "W" pattern, 2 times over and back, 1X around Ronchi: Looks better Press, 7 lbs., 20 min. Work, MOT, same narrow pattern, 1X Ronchi: 25% parabolized per ronchigram from Mel Bartels' DOS program.
24 Feb 2002	Press, 7 lbs., 35 min. Work, MOT, reduced narrow "W" pattern to 1X back forth, 1X around Ronchi: Approaching 50% parabola. It appears that reducing the amount of working reduces lap flow. Press, 7 lbs, 20 min. Work, MOT, narrow parabolizing, 1X Ronchi: Still 50% parabola Press, 7 lbs, 20 min. Work, MOT, narrow parabolizing, 1X Ronchi: Still 50% parabola Press, 7 lbs, 20 min. Work, MOT, narrow, deep parabolizing, 1X Ronchi: Still 50% parabola, slight hole in center. Deep strokes caused hole
25 Feb 2002	Goal is to reduce hole in center Cold press, no weight 50 min. Work, MOT, narrow "W" parabolizing stroke, large rotate between working, 1X Ronchi: Reduced hole, 50% parabolized Cold press, 7 lbs., w/net, 15 min. Cold press, 7 lbs., no net, 15 min. Work, MOT, large shift, 1X Ronchi: Hole reduced
26 Feb 2002	Called Steve Swayze, who suggested lap is too firm. Need softer lap 1/4" thick. Cold press 7 lbs., 35 min. Purpose is to get rid of hole Work, MOT, med parabola, work 2 "W" patterns before turn 1X around Ronchi: Center looks good (hole removed)
2 Mar 2002	Assisted Jim Girard pouring new lap at TM workshop. Used the soft pitch that came with Newport kit. Channeled with soldering iron. Press, 7 lbs., w/net, 30 min. A lot of cerium between mirror and lap. Work, deep parabolizing strokes, 1X Ronchi: Appears to be past 100% parabolized
9 Mar 2002	Made Foucault measurements. Used Fig45 data reduction program. Surface looks poor. Rechanneled lap Cold press, 7 lbs., 15 min. Work, MOT, short over center, 1X, to reduce parabola Ronchi: Little more than 75% parabolized Press, 7 lbs., 15 min. Work, MOT, short over center, 2X, to reduce parabola Ronchi: Still ~75% parabolized. Press, 7 lbs., 15 min. Work, MOT, short over center, 1X Ronchi: No change. Must be melting lap Press, 7 lbs., 15 min. Work, MOT, deep parabolizing stroke Ronchi: No change Rechanneled lap Press, 7 lbs., 15 min. Work, MOT, deep parabolizing, large turns, 1X Ronchi: No change Press, 7 lbs., w/net, 15 min. Work, MOT, deep parabolizing stroke, large turns, 1X Ronchi: No change Press, 7 lbs., 15 min. Work, MOT, VERY deep parabolizing, large turns, 1X Ronchi: Small hole in center.
10 Mar 2002	Rechanneled lap Press, 7 lbs., net, 10 min. Press, 7 lbs., no net, 5 min. Put a lot of cerium between lap and mirror. It seems that additional cerium increased parabolizing. Work, MOT, medium parabolizing stroke, large turns (20%) 1X Ronchi: Looks like 100% parabolized
17 Mar 2002	Steve Swayze suggested oversize lap. If pitch does not flow, no parabolizing. Press 15 min. net, 10 min no net & 7 pounds Work MOT, large W, narrow 1X Ronchi: Edge looks better Press, 7 lbs, 10 min. Work, MOT, medium W, narrow, 1X Ronchi: Parabola ok but still turned edge Press, 7 lbs, 10 min. Work, MOT, medium W, narrow, 2X Ronchi: No improvement
19 Mar 2002	Press, 7 lbs, w/net, 15 min. Work, MOT, large W, narrow, 1X Ronchi: Turned edge mostly gone
21 Mar 2002	Press, 7 lbs, w/net, 15 min. Work, MOT, narrow W at sides, 70 degrees per work, 1X Foucault: Almost no change. Press, 7 lbs, 15 min. Work, MOT, 1X Press, 7 lbs, 15 min. Work, MOT, 1X Foucault: No improvement Lap was way too soft
6 Apr 2002	Repoured lap, Gugolz 64, 3/8" thick Cold press ~24 hours, pitch seems too hard Work, MOT, short strokes over center, 1X Foucault: Slight improvement, center deeper Press, 15 lbs., Work, MOT, medium W in mid range
20 Apr 2002	Cold press 24 hours, no weight Press, 7 lbs, 3 hours Work, MOT, same pattern as Apr. 6 Press, 15 lbs., 30 min. Work, MOT, 1X Foucault: No noticeable change Lap is too hard
28 Apr 2002	Repoured lap. Used old pitch (Gugolz 64), added to caps of mineral oil Cold press with net Press without net, 7 lbs, 5 hours Pitch is a little softer than before
30 Apr 2002	Work, MOT, narrow W at edges, 1X
2 May 2002	Press, 22 lbs, 1 hour Work, MOT, narrow W at edges, 1X (no pressure when working) Foucault: No improvement Press, 22 lbs, 1 hour Work, MOT, X2 Foucault: Center slightly deeper, moving in right direction
3 May 2002	Press, with net, 7 hours Work, MOT, narrow W at edges, MEDIUM PRESSURE, 1X Foucault: No hole in center (good news) Foucault: Center improved quite a bit. Pressure made a difference. Press, with net, 12 hours Work, MOT, medium pressure, 2X Foucault: Much better center Press, 15 lbs., 1 hr. Work, MOT, medium pressure, 2X Foucault: Center better
4 May 2002	Press, with net, 11 hours Work, MOT, medium pressure, 1X Narrow W at sides, and strokes over center Foucault: Lost ground Work, MOT, medium pressure, 2X Narrow W at sides Foucault: Back to where I was Press, 15 lbs., 1 hour Work, MOT, medium pressure, 2X Foucault: Improved
Cinco de Mayo	Press, 9 hours Work, MOT, medium pressure, 2X Press, 5 hours Work, MOT, medium pressure, 2X Foucault: Improved strehl = 0.632 Press, 15 lbs., 1 hour Work, MOT, medium pressure Foucault: better Press, 22 lbs., 1/2 hour Work, MOT, press edge harder by hand Foucault: Slight loss - poor control of pressure on edge Press, 22 lbs., 1/2 hour Work, MOT, long over center, 2X Foucault: Improved center, not edge
8 May 2002	Trying to take down edge Press, 22 lbs., 1 hour Work, TOT, tangent over edge, no pressure Foucault: Center improved, no change in edge Press, 22 lbs., 1/2 hour Work, MOT, placed 7 lbs., weight on edge, narrow W with edge over center 2X around Foucault: Edge improved, strehl = 0.78
20 May 2002	I decided to have Steve Swayze finish the figure of my mirror. This is the end of the mirror log.