卡式鏡的洞

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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simonii
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註冊時間: 週五 19 12月, 2003 18:20

卡式鏡的洞

文章 simonii » 週二 07 3月, 2006 14:01

其實可唔可以完成o左主鏡先鑽?

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august
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註冊時間: 週一 24 5月, 2004 00:12
來自: HK

文章 august » 週二 07 3月, 2006 17:19

我估===
在未磿主鏡前,已經鑽o左一半(未鑽穿)。當完成測試後。先至鑽小孔

Chanlunlun
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Re: 卡式鏡的洞

文章 Chanlunlun » 週二 07 3月, 2006 22:04

simonii 寫:其實可唔可以完成o左主鏡先鑽?
Dear Mr. Simonii,

The best way to make the central hole in a Cassegrain primary is to drill it AFTER the mirror has been fully polished and parabolized. In this way you save a lot of troble in making the lap. Polishing and figuring will also be much more easier.

I had made a Cassegrain primary before (33 years ago !! ) The hole, with diameter 2 inches, was drill after the mirror was fully polished and figured.

I never finished or had the interest to finish the secondary mirror since a barlow lens can serve same the purpose very well. Why bother to make the difficult hyperboild secondary ?

Best regards
Chan Yuk Lun
附加檔案
7_1.jpg
The 33 years old 7 inch Cassegrain primary. Nevertheless it is used as a Newtonian primary. You can still see the red rouge sticking on the edge of mirror.
7_1.jpg (44.26 KiB) 已瀏覽 6622 次

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豆豸苗
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文章: 9950
註冊時間: 週六 28 6月, 2003 02:29

Re: 卡式鏡的洞

文章 豆豸苗 » 週三 08 3月, 2006 00:23

simonii 寫:其實可唔可以完成o左主鏡先鑽?
有聽聞會因應力問題所以鏡面會變形? :? 不過我未試過, 唔知真假.
用鑽石鑽來鑽, 有可能鑽花或鑽崩少少邊. 落鏡那面的邊會較少崩, 底面的邊會較多崩口.

前輩們那一代好像都是用鐵通+鋼砂鑽窿的. 可能會好一點, 沒那磨容易崩. :?

我之前做的 gregorian 同宜家仲整緊0既卡式都係鑽左先磨.
gregorian 那塊主鏡本打算在粗磨完後由鏡背鑽下去, 但結果鑽崩了鏡面(因為下面沒東西墊著). 然後唯有將鑽了出來的玻璃補回去再粗磨, 幼磨, 拋光.

亦有聽聞先鑽一半, 拋好後再鑽穿. 這做法要看由鏡背/鏡面鑽穿. 由鏡背鑽下去就要小心有上面 gregorian 的情況鑽崩鏡, 如由鏡面鑽下去就要小心有可能和另一面接合不好. 接合得不好會影響裝上遮光筒的精度.

也有聽聞有人是窿到剛剛好, 到拋光時中間那塊玻璃自然掉下來. 但我試過磨穿那一刻, 其實是不會那麼"乾脆"的. 會有一段裂開的過程, 所以如果不想鏡中間的洞的邊崩, 更加不想拋光途中鏡面被裂開的玻璃刮花的話. 這方法似乎不太可行.

所以我現在做的卡式主鏡是先鑽大半的厚度, 補上白英泥, 然後再開始磨, 粗磨時會磨到白英泥部份, 磨到 220 號時會再挑走一點白英泥, 再補新的, 以免之前的粗沙埋在白英泥內 (因為白英泥之間有氣泡). 一直磨到拋光, 白英泥處會越來越滑, 就好像和玻璃溶為一體一樣. 補了英泥的鏡倒模沒大問題. 但到拋光時, 你會發覺白英泥比玻璃磨蝕得快一點點(很少), 近中間的洞會有少少"低邊", 但因為會被中間的遮光筒遮著, 所以沒大影響. 反而如果一開始鑽了窿而沒有補, 磨砂會流到中間的洞, 就算你有辦法倒模, 中間的"低邊"會十分嚴重, 也很難救(即是 chan sir 所講的很難 figure).

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simonii
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文章: 647
註冊時間: 週五 19 12月, 2003 18:20

文章 simonii » 週三 08 3月, 2006 00:38

I never finished or had the interest to finish the secondary mirror since a barlow lens can serve same the purpose very well. Why bother to make the difficult hyperboild secondary ?
這的確省了不少工夫, 但barlow 夠大面積嗎? 會否有漏光的情況出現?
有聽聞會因應力問題所以鏡面會變形? 不過我未試過, 唔知真假.
我就是擔心這個問題不知影響有多大
我估===
在未磿主鏡前,已經鑽o左一半(未鑽穿)。當完成測試後。先至鑽小孔
聽落好似有道理...

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豆豸苗
夸克星
文章: 9950
註冊時間: 週六 28 6月, 2003 02:29

文章 豆豸苗 » 週三 08 3月, 2006 00:46

simonii 寫:
我估===
在未磿主鏡前,已經鑽o左一半(未鑽穿)。當完成測試後。先至鑽小孔
聽落好似有道理...
留意== "這做法要看由鏡背/鏡面鑽穿. 由鏡背鑽下去就要小心有上面 gregorian 的情況鑽崩鏡, 如由鏡面鑽下去就要小心有可能和另一面接合不好. 接合得不好會影響裝上遮光筒的精度."

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Subaru
夸克星
文章: 6675
註冊時間: 週三 02 7月, 2003 19:27

Re: 卡式鏡的洞

文章 Subaru » 週三 08 3月, 2006 01:40

Chanlunlun 寫:I had made a Cassegrain primary before (33 years ago !! ) The hole, with diameter 2 inches, was drill after the mirror was fully polished and figured.
:shock: 塊鏡差唔多老過我!

Chanlunlun
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文章: 3839
註冊時間: 週四 09 10月, 2003 21:06

Re: 卡式鏡的洞

文章 Chanlunlun » 週三 08 3月, 2006 08:56

Subaru 寫:
Chanlunlun 寫:I had made a Cassegrain primary before (33 years ago !! ) The hole, with diameter 2 inches, was drill after the mirror was fully polished and figured.
:shock: 塊鏡差唔多老過我!
Dear Mr. Subaru,

This 7 inch mirror was made at the same time while WongSir made his 6 inch Newt-Cassegrain. Yes it is a very old mirror. But the telescope is still in active service today.

Origially it was a simple Newtonian. Due to the lack of quality barlow ( no ED lens ) and long eye-relief short focal length eyepiece it was very inconvienient for lunar and planetary observation. Hence it was later decioded to convert it into a Cassegrain. The hole was drilled later after the mirror had been put in service for a year.

I drilled the hole by a stainless -steel tube fed by #80 carbo. The drill was a hand driven one with a speed of 1 round per sec. I drilled th ehole with very gentle force applied and operated very carefully.

If you are using powered tool you most probably end up with a chipping edge on the hole.

Best regards
Chan Yuk Lun

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