Made a ground glass yesterday.....

[Joe Forks]

Ian,
I think it was just ME having problems staying in the corners. Looks like two corners could use a little more grinding, but the other two are good to go. I spent 5 hours grinding this glass. I knew a 12x20 would take some time, still I got impatient.

I didn't measure the old screen, but this pops right into focus in the backyard without a dark cloth. For sure it's brighter, but not sure how much.

Here's a couple photos one with a flash and w/o

[Nathan Potter]

A grooved lapping tool will work a bit better than another piece of glass - the idea being that any slightly larger pieces of lapping debris will become trapped in the grooves and not scratch the glass as you grind away. 3 to 5 um grit is fairly fine so will show a brighter and finer image but more of a "hot" spot than the more typical 600 or 320 grit.

I use a grooved stainless steel block for the purpose. Any hard material will do. Mainly you want the grit in water solution to move freely and randomly between the tool and the glass, while the depth of the grind damage is a function of the force you put down on the tool. Hence a heavier tool is easier on the arm.

Nate Potter, Austin TX.

[cosmicexplosion]

can you use a buffer and grinding paste like you use for engines?

ia there an electric option?

[Jack Dahlgren]

can you use a buffer and grinding paste like you use for engines?

ia there an electric option?

I just gave it a try with a random orbital sander.

In 30 seconds or so 60 grit gives a reasonable opacity.
100 grit polishes too much and results in being able to clearly see the lens opening rather than just the projected image.

The problem is that it is not truly random so there is an underlying swirl pattern that is visible. At least that was the case with my short experiment.

If I were going to do it I might use 100 grit with electric assist for the first step and then finish by hand.

[Daniel_Buck]

just curious, I wonder if glass etching compound would work and provide a decent view?

[Jack Dahlgren]

just curious, I wonder if glass etching compound would work and provide a decent view?

It might, but you don't want to etch very deep. It is easy to try...

[IanG]

I just gave it a try with a random orbital sander.

In 30 seconds or so 60 grit gives a reasonable opacity.
100 grit polishes too much and results in being able to clearly see the lens opening rather than just the projected image.

The problem is that it is not truly random so there is an underlying swirl pattern that is visible. At least that was the case with my short experiment.

If I were going to do it I might use 100 grit with electric assist for the first step and then finish by hand.

Using a power tool is over kill and not random enbough, it's so easy to grind a 10x8 screen by hand, it takes me about 10 minutes maximum.

You need #400 grit or finer. I'll be back to the grinding next week

Ian

[GPS]

Using a power tool is over kill and not random enbough, it's so easy to grind a 10x8 screen by hand, it takes me about 10 minutes maximum.

...
Ian

First you say building bellows is easy, now you say even grinding one's own gg is easy - if you say tomorrow that building your own camera is easy I think I will stop reading that...

[IanG]

First you say building bellows is easy, now you say even grinding one's own gg is easy - if you say tomorrow that building your own camera is easy I think I will stop reading that...

Well as I restore cameras and learnt from scratch what can I say

Actually I think I'd find building a camera rather challenging but I could get the wood work done very economically. I've had replacement parts made, like a new front standard for the Quarter plate camera in the Bellows thread. A good cabinet maker could make all the parts very quickly.

So no plans to make new cameras I find the late 19th C British field cameras are good enough, I'll make a new 5x4 back and a 6x17 back for my Half plate camera in the same way as I made a conversion plate to allow the use of a 120 Graflex RH10 back on my Quarter plate camera.

Back to screens though, grinding your own is so simple and you can easily match the best available, I was a little sceptical and initially planned to buy a few screens from Belgium (GVB) I already had a Steve Hopf screen. However I needed about a dozen screens so potential costs began mounting, so I decided to have a go. A dozen screens 9x12 cm up to 10x8 cost me a less than £20 ($31(

Because I was making a number of screens I was able to grind and compare using different grits and degrees of grinding. Often a double grind with #400 then #600 grit gives a good all-round screen.

Glass & grits are very cheap so it's easy to experiment and see what suits you best. In my case my screens have given many pre-WWII cameras a new lease of life, and my Graflex's (pre & post WWII) are now so much easier to focus.

Ian

[Nathan Potter]

Ian, the 360 to 600 grit range is what I have found most useful - same as your experience. Never tried multiple grinds with different grits on the same plate; that would be interesting - yielding a mix of fracture densities.

Daniel, what is in the glass etching compound that would etch glass? The classic etchant is HF, hydrofluoric acid, very nasty stuff. Using the vapor to etch the glass will yield a frosted appearance on the surface but it scatters the light poorly so yields a very hot center spot in viewing - my experience from actually trying it in a proper fume hood. I think direct wet etching of the surface with HF solution may be used for anti newton fabrication where there is virtually no scatter centers formed but just broad area etching to reduce the intensity of the interference.

Maybe some one here knows the details of the anti newton glass process.

Nate Potter, Austin TX.