6 hrs of rough grinding of 24 in mirror

自製天文望遠鏡 牛頓望遠鏡 杜蘇式 卡式 設計和磨鏡方法<br>
佛科試鏡法 佛科刀片儀 光柵試鏡法 光柵片
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Chanlunlun
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註冊時間: 週四 09 10月, 2003 21:06

6 hrs of rough grinding of 24 in mirror

文章 Chanlunlun » 週六 07 2月, 2004 20:26

DearATMs,

Rough grinding was carried on today, as per schedule. Our mirror grinding room is a bit small and so it creates a little problem while we were 「walking around the table」. Anyway we managed to finish the 5 hour of rough grinding, 1 hour running ahead of the original schedule.

Important data arrived – after totally 6 hours of rough grinding we had generated a f/11 curve on the 24 inch mirror which means that 30.8 cubic inch of glass had been removed away. Simple calculation shows that the glass removal rate is about 5 cubic. inch per hour. To obtain a f/3.5 curve 97 cubic inch of glass has to be removed, meaning that we require totally about 20 hours of rough grinding time. It sound quite logic and fits my intuition.

5 lbs of #40 carbo was consumed in 4 hours. The carbo consuming rate is about 1.3 lb per hour. Hence to produce the f/3.5 curve at least 26 lbs #40 carbo is needed, a cost of HK$ 520, 12% the total construction cost of the whole telescope. It also sounds right.

We have to make such calculation to monitor how much we are going spent and to allocate the right time for the student』s shift.

Another 4 hours of roughing is scheduled tomorrow and hopefully a f/7 curve will be arrived at after the roughing, as per calculation.

Below is the formula used to calculate the volume of glass has to be removed for a given f/number of any mirror:-

Volume of glass to be removed = (3.142)(r)^3/(16 x f/no.)

Best regards
Chan Yuk Lun
7-2-2004
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sodium_24in.jpg
Mr. Sodium was working very hard at the 24 inch mirror inside the small mirror grinding room. The 24 inch tool was held in place by newspaper.
sodium_24in.jpg (54.81 KiB) 已瀏覽 11118 次

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豆豸苗
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文章 豆豸苗 » 週六 07 2月, 2004 21:35

wa. Sodium 喎~~~~ :shock:

推起上0黎重唔重呢? :? :? :?

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sodium
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文章 sodium » 週日 08 2月, 2004 13:12

豆豸苗 寫:wa. Sodium 喎~~~~ :shock:

推起上0黎重唔重呢? :? :? :?
推就小小重law

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Wah!
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文章 Wah! » 週日 08 2月, 2004 20:50

換砂就一定係勁重啦!

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Subaru
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文章 Subaru » 週日 08 2月, 2004 21:24

Wah! 寫:換砂就一定係勁重啦!
又係, 磨到600同1200果陣重危險.

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豆豸苗
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文章 豆豸苗 » 週日 08 2月, 2004 22:08

係喎... 如果磨到 600 同 1200 時, 磨得慢0的都好易癡住...
癡住左點算?? 咪要好多熱水?? ^^||||

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Subaru
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文章 Subaru » 週日 08 2月, 2004 22:30

豆豸苗 寫:係喎... 如果磨到 600 同 1200 時, 磨得慢0的都好易癡住...
癡住左點算?? 咪要好多熱水?? ^^||||
P = F / A

24"真係唔知點攪! :shock:

Chanlunlun
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註冊時間: 週四 09 10月, 2003 21:06

文章 Chanlunlun » 週日 08 2月, 2004 22:47

豆豸苗 寫:係喎... 如果磨到 600 同 1200 時, 磨得慢0的都好易癡住...
癡住左點算?? 咪要好多熱水?? ^^||||
Dear Miss BeanKitty,

Thanks for your concern. The best way to avoid mirror sticking is to not letting them stick. During #600 onward we use a lot of carbo and water to avoid drying up. Sticking arise due to drying up of water between the mirror and the tool.

If sticking does occur we can still separate the mirror and the tool easily by holding the assemby at about 1 feet from the floor and then release your hand. The whole assembly will free fall onto the floor and upon hitting the floor the impulse will make the mirror and the tool separate automatically.

Sounds terrible? Don't worry, I always did this on my 20 inch mirror( and the 14 inch ) when it got stucik with the tool.

One thing I forgot to tell you - the floor I mentioned must be a wooden floor. If not, place a piece of wood where the mirror you think will hit the ground.

One last thing - we cannot use hot water. A mirror that big when receive sudden heat will crack easily.

Best regards

Chan Yuk Lun
8-2-2004

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豆豸苗
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文章 豆豸苗 » 週一 09 2月, 2004 14:11

咁樣整開塊鏡同塊工具板? :shock:
真係幾匪夷所思啊~~~ ^^ 不過我相信前輩0既經驗0既~~~~!

其實除左不斷 keep 住加水用砂, 加多0的"揀"水可唔可以減低佢地癡住0既機會呢?

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Wah!
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文章 Wah! » 週一 09 2月, 2004 14:12

"揀" 意思係肥皂.

Chanlunlun
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文章 Chanlunlun » 週一 09 2月, 2004 17:44

豆豸苗 寫:咁樣整開塊鏡同塊工具板? :shock:
真係幾匪夷所思啊~~~ ^^ 不過我相信前輩0既經驗0既~~~~!

其實除左不斷 keep 住加水用砂, 加多0的"揀"水可唔可以減低佢地癡住0既機會呢?
Dear Miss BeanKitty,

Thank you for your comment. However I'm afraid that soap solution cannot help in avoiding mirror srticking problem. As I've mentioned before mirror sticking arises from the drying up of liquid between the mirror and the tool. So there are tow ways out :-

1. Use a lot of water and carbo and replenish as frequent as possible to avoid drying up.

2. Use non-volatile liquid, such as kerosen, instead of water for fine grinding. While it is true that kerosen is non-volatile we must not assume that it willl never dry up. Sooner of later kerosen will vaporize eventually, mirror sticking still occur.

Instead of a messy business, mirror grinding needs a lot of care.

Best regards

Chan Yuk Lun
9-2-1004

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Wah!
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文章 Wah! » 週一 09 2月, 2004 22:48

用油得唔得呢???

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