Course GG...

[Robert A. Zeichner]

You basically prepare a paste (more like a slurry) of super fine aluminum oxide abrasive and grind it into the gg with circular motions. For abrasive, you can get 5 micron and 3 micron aluminum oxide from Willmann-Bell in Richmond VA. Cost will be around $20 for 8 oz. of each (a lifetime supply). (804) 320-7016 is their phone. I made a grinder by cementing a golf ball to an old 2x2 Tiffen filter using some PC7 two part epoxy. The ironic thing is that PC7 has been around for decades and many hardware stores have a product sample that consists of an old 7up bottle with a (you guessed it) a golf ball glued to the top. I jokingly asked the hardware salesguy "do you have anything I could glue a golfball to glass with?" Made his day. Anyway, you take about a 1/4 tsp. of the abrasive and add some water with an eyedropper until you have a slurry that is similar in consistency to light, runny cream. Put the gg down on some layers of newspaper sitting on top of a solid flat surface like a piece of plywood. If you sprinkle the paper with a bit of water, that will help hold the glass from moving around. Just start on one corner and using circular motions work your way back and forth until you have covered the whole gg. You will need to add a few drops of water from time to time and you will also have to grind for about a half hour until you see the results you want. Start with the 5 micron abrasive and examine after grinding to see if meets your expectations. You can wash the gg in water and dry with an old t-shirt and then examine with a loupe. I designed some patterns in my computer which I then used as a template to draw fine lines on the ground side of the gg with a .05mm mechanical pencil. Works great.

[C. D. Keth]

Wonderful. Thank you

One more question. I can find lots of places that supply Al oxide in grits of 400, 600, 800, et cetera. Do you know what those equate to (approximately) in micron grain sizes?

[Robert A. Zeichner]

I can't really say. 400, 600 and 800 sound like abrasive paper grits to me (wet-or-dry) which you don't want, but perhaps they mean something to someone more familiar with grinding supplies. What you are in need of is abrasive powder. I would just call Willmann-Bell and ask them. They also have a catalog which they will send and that might have the answers you seek.

[Glenn Thoreson]

The Satin Snow glass is a very fine product. I love mine. I have, on many occasions, needed glass in a hurry and have made my own. You can probably improve your existing glass easy enough. Get a small tube of fine valve grinding compound from the auto parts store. Remove your glass from the frame. Lay it on an abolutely flat surface. padded with 3 or 4 sheets of newspaper. Put a little water on the glass, and a dollop of grinding compound. You will need another piece of glass to grind with. About 4X5 or so will do. Size is not critical. Place it on your glass and just start rubbing around in random circles, trying not to make a single directional motion. Do not put pressure on the rubbing glass! Only enough to keep it down in contact with your focus screen.. Keep a good film of water on it. Don't change, or add to, the compound.
Rub round and round until the gritty feel is pretty much gone. Wash it off with water and a little dish soap. Let it dry by itself. If you rubbed till the compound was worn out, you should have a smooth, very fine finish. If the glass is not flat (common) and has low spots that were missed, just give it another go.
It's easy and works well. Good luck.

[Robert A. Zeichner]

Here is a link to Dick Dokas' complete article. In it there is a chart that crosses abrasive grades to particle size.
http://www.dokasphotos.com/techniques/ground_glass/

[Paul Fitzgerald]

Hi Chris,

Silicon carbide also works well for grinding a GG view screen, just look in the phone book under lapiday for a rock & gem store, about $8.00 lbs.

400 grit is fine
600 grit is very fine
800 grit is ultra-fine
1000 grit is polishing, too fine.

A hardware store should have 3M 'SandBlaster' brand sand paper, it's purple. It is great for grinding the edges of the glass smooth, 150 grit. Just back it up on another larger piece of glass and run it lengthwise, not across the edge A black Sharpee to edge-black the glass and you're good to go.

Have fun with it.

[C. D. Keth]

Thanks for all the info guys! I found a good supplier of abrasive grits (gotgrit.com). They are mainly a supplier for amateur telescope making. $12 got me what I need.