The making of 30 in telescope - 24, Paraboloid is coming.

[Chanlunlun]

Dear ATMs,

After 37 hours of figuring the central bulge of the oblate spheroid has been removed and the high edge zone was also lowered a lot. That is to say the paraboloid starts to take shape.

It has been a laborious 37 hours. Not only that we had to work in hostile environment but also that we need to supply great force to the lap in order to remove glass as quickly as possible. Fortunately the use of brutal force ends here and from now on we enter the second stage of figuring – the making use of small lap to cure the zones left after the rough figuring.

For the first time we feel the approaching of the end of battle and, of course, we set no time limit to when to end this war as things will always happen during our fight.

Best regards
Chan Yuk Lun
17-8-2005

[oldsaltfish]

Do you want to make a small tool?

[Wah!]

He must already have made small tools.

[Chanlunlun]

Do you want to make a small tool?

Dear Mr. Oldsaltfish,

Yes I have already made one - 1.5 inch diameter, for getting rid of the turned down edge.

Best regards
Chan Yuk Lun

[豆豸苗]

1.5 inch diameter? Very small le!!!!
Nearly smaller than the tool for my gregorian secondary!

[Chanlunlun]

1.5 inch diameter? Very small le!!!!
Nearly smaller than the tool for my gregorian secondary!

Dear Miss BeanKitty,

1.5 inch lap is not the smallest lap we are using. We will use a 1 inch lap for precise figuring of the edge.

Indeed one inch lap is too small to handle. We are thinking of using our finger to figure the mirror.

The finger is really small, the smallest lap ever used in mirror figuring.

Best regards
Chan Yuk Lun

[豆豸苗]

Yes. really hard to handle such small tool!
My secondary's tool is 1 inch in diameter, the pitch on top of it can easily be detached from the glass.

It is also hard to control the force while you have to avoid the tool from slipping off your finger....||||
I can imagine using finger is much more direct.

But sounds that it would be a terribly long figuring process by using finger to get rid of the edge?

[Chanlunlun]

But sounds that it would be a terribly long figuring process by using finger to get rid of the edge?

Dear Miss BeanKitty,

Yes it really does. Turn down edge is the worst nightmare to deal with. Using finger is the most direct and effective measure. Try to imagine how much glass we need to remove in a 30 inch mirror you will undrestand why we must use extreme measure.

Actually Alvan Clark used to favour finger figuring in making his 36 inch ( Lick observatory ) and 40 inch lens (Yerkes observatory ).

Best regards
Chan Yuk Lun