天文望遠鏡製作 2007 (第九課-實習課4) 17 June 2007

layanata · 文章由 **layanata** » 週日 17 6月, 2007 15:49

不好意思啊, 這兩日去了坐井Camp, 因為太夜沒有通知黃sir我不能前來磨
鏡班, 今天豆貓有來嗎? 煩請各位報告一下今天情況和貼一些相片, 感激感
激啊!

文章由 **Wongsir** » 週日 17 6月, 2007 15:55

Layanata,

Doucat and Wah are with us now.

Wongsir

papaya · 文章由 **papaya** » 週日 17 6月, 2007 22:25

Wongsir 寫:Layanata,

Doucat and wah are with us now.

Wongsir

今日學 "W" 磨鏡法, 但是中間凸咗, 唔知大家有何高見.

tommy_tse · 文章由 **tommy_tse** » 週日 17 6月, 2007 22:32

Today, I have learned quite a lot. Mostly importantly, Wong Sir said he had put money in my pocket and I have "absorbed" five years of his experience in just a few minutes. Let me tell you how in the following picture narratives.

tommy_tse · 文章由 **tommy_tse** » 週日 17 6月, 2007 23:03

I began today with sand #320. I started at 10:15 am and completed #320 at 3:15 pm with one hour and 15 minutes lunch break. In total, I had done 17 runs of 4 minutes and 30 seconds each to complete #320 polishing stage.

After 3 runs, Wong Sir taught us to use W-Stroke instead of Diametral Stroke so that we could get familiar with W-Stroke to do fine correction on mirror and tool matching as well as circular zoning problem.

My dearest tutor Choi Sir also examined my mirror after the 8th runs. The grains were unevenly distribured with better polishing in the center than the rim. I then continued with another 3 runs (a total of 11 runs completed before lunch) with the last run turning the tool on the top to polish the main mirror as instructed by Wong Sir. That works very well and the grains were evenly distributed.

tommy_tse · 文章由 **tommy_tse** » 週日 17 6月, 2007 23:04

After lunch, Wong Sir taught us to use pencil line polishing method to test degree of matching of both the mirror and tool at #320 stage. You can see my bubble test was excellent but it was not accurate enough at 320 stage. The pencil test on my mirror failed as the pencil markings on the rim remained after about 20 “dry” strokes with 10 strokes in two different direction.

豆豸苗 · 文章由 **豆豸苗** » 週日 17 6月, 2007 23:05

papaya 寫:今日學 "W" 磨鏡法, 但是中間凸咗, 唔知大家有何高見.

有可能 W 磨程磨到中間時行得太密?
不過 W 磨法0既手勢唔同人會有好大差異. 所以要搵到原因真係要試, 試下用唔同磨程, 長形闊形, 中間濶/窄0既 W 形, 或者模上鏡下又試幾轉睇效果先可以判斷到要用乜野手法磨走凸出的部份.
但如果試左好耐 W 手法都唔掂時, 正如蔡sir 今日咁講, 轉返用 1/3 正心最穩陣.

tommy_tse · 文章由 **tommy_tse** » 週日 17 6月, 2007 23:09

I did another 5 runs of W-Stroke and the pencil mark testing still could not pass. This time with the rim markings gone but the center markings were left behind after dry strokes. A few students encountered the same problem around the same time like me. Choi Sir was wondering what had happened to us and told us to do one run of Diametral Stroke – the problem vanished and it looked perfect with all pencil markings gone on the center and rim! Nice going, Choi Sir!

Here is a picture of the grain size after the final pencil mark testing.

tommy_tse · 文章由 **tommy_tse** » 週日 17 6月, 2007 23:20

Wong Sir said there are a few common mistakes we made when polishing #320:
(1) Too much sands so the tool and mirror were “lifted up” by the sands so polishing became uneven;
(2) We did not got rid of the bubbles between the two glasses so not all surface area were polished;
(3) We used too much or not enough water.

Wong Sir demonstrated below what an evenly distributed sands looked like without air bubbles. Don’t forget not to talk on the phone like Sky Observers’ Club past chairman Wong Sir – the two glass pieces would get sticked togther when left unattended for a while.

Our tutor Wah! Also showed us how to get grid of the air bubbles by moving the mirror too one side and then self-turning it once to get rid of the bubbles. I found this working quite well.

tommy_tse · 文章由 **tommy_tse** » 週日 17 6月, 2007 23:26

Before I started on sand #600, Wah! and 豆豸苗 helped us to measure our mirror’s focal length by measuring the radius of curvature using light test. My mirror’s radius of curvature was 1460 mm, which is 2 times its focal length. The standard f/6 with 120 mm mirror required 720 mm focal length. I was fortunate to accidentally achieve a focal length of 730 mm!

tommy_tse · 文章由 **tommy_tse** » 週日 17 6月, 2007 23:33

Wong Sir also showed us how to measure the degree of matching of the two glass pieces by reflection test under a florescent lamp to see if the refelction of the “red florescent lamp” brightness was even when moving the mirror left to right or vice versa. Don’t use pencil mark testing as it may scratch the mirror!

tommy_tse · 文章由 **tommy_tse** » 週日 17 6月, 2007 23:35

Look at this guy, he pretended to look like wong sir but I bet he did not know what he was doing! Wong Sir told this guy to go home and polish #600 and #1200 two hours each and forget about the reflection testing. Poor guy!

tommy_tse · 文章由 **tommy_tse** » 週日 17 6月, 2007 23:39

Wong Sir also showed us how to examine the grains of #600 above by back lighting via a 10x loupe. Wong Sir said he hated this as the bright light hurt his eyes and he will only demonstrate to us once.

Here is the picture of the #600 grains after 2 runs of 4 minutes and 30 seconds each.

tommy_tse · 文章由 **tommy_tse** » 週日 17 6月, 2007 23:41

Here is a picture of how much #600 sands (mixed with liquid soap solution) were being used in a single polishing run.

comp_soc · 文章由 **comp_soc** » 週二 19 6月, 2007 01:47

我都就來要開工啦, 磨 600號...我想問如果要調制 600 sands solution, 係唔係菲林筒加沙加水, 搞到 "傑傑"地, 之後就就一,兩滴洗潔精呀 ?

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