Making and Testing Flat Mirrors

Hi guys,

I’ve made some progress in figuring my 10” flats and have knocked up a page showing the results of my efforts. I am concenting on figuring just one plate at a time rather than all three together and also increased the length and width of my stroke to 1/2W x ½ side-to-side. The results amazed me! Figuring flat mirrors is supposed to be much harder than working a paraboloid, but I just can't agree - this has been a walk in the park... so far! I now have one plate at around ¼ fringe (or 1/8 wave at 589nm) from flat and have started work on the next plate. I was worried that I would end up with TDE with such a long stroke, and indeed it did show up briefly on one plate, but I think I have it licked. I can see no trace of TDE in the later interferogram images.

Phil.

ochra.110mb.com/figuring_log_for_10.htm

Thats seriously impressive Phil. The improvements as you progress with the figuring is particularly marked. Keep up the good work!

Interesting work Phil. It's something I'm interested in because I have a couple of 8" blanks I hope to grind into mirrors some day. Where did you get your 10" flats from? Didin't you have another webpage showing your progress before? I would be interested in seeing your equivalent of a blog on this project.

Seanie.

Interesting work Phil. It's something I'm interested in because I have a couple of 8" blanks I hope to grind into mirrors some day. Where did you get your 10" flats from? Didin't you have another webpage showing your progress before? I would be interested in seeing your equivalent of a blog on this project.

Seanie.

The original page is still there - the link is at the top of the new page where it says Click 'here'...

I got my blanks (1" thick float glass) from Galvoptics in the UK www.galvoptics.fsnet.co.uk/ . They also supply abrasives and polishing compounds. Galv can be a bit slow to respond to small orders and so I have started using GotGrit www.gotgrit.com/ in the USA as they are totally ATM oriented and very fast to respond. The guy who runs it is an ATM on the ATM mailing list... which itself is a great resource.

If you have two equal thickness 8" blanks then don't use one as the tool - make another mirror out of it! For a tool, use a large floor tile (or lots of smaller ones!) and a couple of inches of concrete. This is dead easy to knock up and use. If you need a big tile cut to a circle, I can do that with an angle grinder for you. Don't waste that good blank!

Phil.

Thanks for keep us apprised of that Phil, its an interesting area of astronomy that gets little air these days, so its great to see some one at it.

Thanks Phil, good to know about the tiles+concrete combination for a tool. I would have never thought that combination would have measured up to a glass one!