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.

006-Pitch_On_Tool

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.

008-Polishing

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.

010-Inside-ROC

011-Outside-ROC

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.

012-Weight

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.

013-Lap

014-Inside-ROC

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).

015-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.

016-Inside-Roc

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

017-Inside-Roc

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

018-Inside-Roc
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

019-Inside-Roc

020-Roc

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.

021-Inside-Roc

022-Roc

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.

023-Inside-Roc

024-Roc

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

 

025-minus3-Roc026-minus1-Roc027-plus3-Roc028-plus5-Roc029-Ronchi

 

 

 

 

 

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.