what grit for ground glass

[Peter De Smidt]

Good stuff, Randy! When I get some time, I'll make some comparisons of a 3 micron aluminum oxide glass, a Sinar glass, a Maxwell screen, and a Beattie Intenscreen +.

[Fr. Mark]

Reviewing some older DIY threads. You guys amaze me. I tend to think of float glass as a flatness standard and here y'all
Are talking about flattening it!

Two possibly dumb ideas:
Sandpaper will grind glass too. I used it because it was available. To make grid lines, draw them on with a pencil and a straight edge.

Scribing grid lines with a needle sounds to me like an invitation for the glass to snap on those lines.

A couple more dumb ideas: don't use glass, use acrylic (it scratches easily!), or waxed or oiled paper (durability issues) or a matte or flat varnish on glass etc.

[Tim Meisburger]

Okay. I finally got around t ordering this. I got the one Peter recommended (called pre-polishing), and after I made the order the invoice showed it as 3 micron powder (.0001) rather than 5. I hope it is not too fine!

Unfortunately, I am off on a work trip Friday, so will not have a chance to try it till I return in early November.

[Tin Can]

Made a new 8X10 GG last night from Home Depot 8X10 which exactly fits 8X10

I made cut corners first, as I like them. First to check aperture and secondly to make less suction pulling in dust

Used what I had already 600 grit from this source which sells to telescope mirror makers, lot of good info there

https://stellafane.org/tm/atm/mirror...20Size%20Table

Used the GG today, it is very nice, but I plan to use even finer grit and see what I like

I have made at least 5 GG up to 11X14

[Ron (Netherlands)]

Have 400, 600 and 1000 (silicon carbide). Especially for smaller glasses, such as a little ground glass for a Rolleicord, I use first 600 and then the 1000 to get a smooth surface.


Ground Glass XVI by Ron (Netherlands), on Flickr

this one was done for a Deckrullo camera which had rounded corners:

Ground Glass VIII - Nettel Deckrullo by Ron (Netherlands), on Flickr

[martiansea]

I just made this one for my B&J 5x7 using aluminum oxide from gotgrit.com and I am very pleased with how it turned out. Image is nice and clear and I see very obviously much finer granularity when compared to the stock gg on my Cambo, and it's in a completely different league than the crummy vintage one it is replacing.
Since the oxide grit is stupidly cheap in the tiny quantities I needed for this (1/4 pound will probably make 100 ground glasses), I got 5 different grits, ranging from 25 micron to 5 micron. I didn't even get down to 5 micron with this. I went from 25, to 15, to 12 and then I was happy enough with it, I didn't see any reason to go further. Next one I make, I'll take it all the way down to 5 micron and see if it makes enough difference to be worth the extra time. All told, it really didn't take as long as expected, maybe a half hour grinding at 25 micron got a functional gg, and just a bit longer with the finer grits to finish it off. Maybe 2 hours work total, that includes washing it off and drying it several times to check on the progress.

[Peter De Smidt]

Thanks for the report!

[Jim Noel]

I have heard that finer grinds reduce graininess, but also decrease brightness and increase apparent fall-off, but I haven't seen any disadvantage to the finer abrasives yet.

If I can find them I will try installing the cheap page magnifier fresnels I bought too.

Be careful - the way you install the fresnel may change the point of focus so that your images are out of focus.

[Jim Noel]

I started making my own ground glasses during WWII when it was difficult to find it readymade. I make 2 at a time using one to grind the other.. I usually cut the corners before grinding, but have been known to do so after grinding. I have also made them using spray-on window frosting, which works well, but is fragile.

[Peter De Smidt]

I've not tried the spray on method. Other than the fragility, how does it compare?