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Re: [ATM] Sand-blasting a mirror blank
The curve is more like F1.5 (72" ROC) or thereabouts with a 1" sag.
You could do a corrector plate but that can be fun at that short a FL.
Better would be to drop by Harbor Freight and pick up a 3 piece set of their
4" diamond disks and use them to grind the glass a lot flatter. I'd use a
low voltage DC motor if possible to drive the disk if you want to build a
ROC curve generator which you can probably do for a bit less than $100 if
you do a decent job of scrounging. Peter John Smith has a nice article on
curve generation on his website and you will want to look at his method of
cupping a disk so that it will not hit in the center as you do your
grinding.
Lastly, you can use the disks by just gluing one of them to a piece of wood
or steel, as desired, and get the Popeye arms. I've got one guy that is
using one of the disks that way on a 15" porthole glass.
Bob May
bobmay@nethere.com
http://nav.to/bobmay
http://bobmay.astronomy.net
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