On flickr I've put up a little howto on making ground glass screens yourself:
https://www.flickr.com/photos/zorki_...57660810886723
On flickr I've put up a little howto on making ground glass screens yourself:
https://www.flickr.com/photos/zorki_...57660810886723
Nice!
DIY is the best for GG. I have made 6 up to 11x14.
Tin Can
Thanks Randy, the biggest I made until now is 10 x 15 i.e. cm :-)
the smallest is the one made for the Rolleicord: 64 mm x 56 mm.
cheers
Ron
Many thanks for that, very self explanatory even without the text.
Mick.
Thanks! Will use this to make my first GG.
Will Whitaker got me started on this eons ago…even supplying me with a it of grit to get me going (thank you Will!).
As I cannot find text for the OP’s entry, I’ll share the following. Keep in mind that this is what works for me, and that other’s mileage may vary.
Extremely simple matter of applying about a teaspoon of grit (#500 carborundum I think) to an oversized (larger than target GG) sheet of plate glass…adding slightly more than the same volume of water (some use oil, but water works for me), mixing slightly, then laying atop this the cut-to-sized sheet of “future ground glass” - and gently, with fingers of both hands (thin nitrile gloves help with lateral friction) moving this top sheet against the bottom in a circular motion. Its amazing how a small amount of grit can spread out!
A few hints (again, this is what works for me):
- As you rotate the top glass, try to spread downward finger force as evenly and broadly as possible, and slightly shift finger position occasionally. You want to spread this force as evenly as possible. Again, nitrile gloves help with this. (hmm…makes me think that a GG-sized thick board, with a sheet of neoprene glued to it (to press against the glass), would be really handy here!)
- Allow the center of rotation to drift slightly during the grinds. You want to introduce an aspect of randomness to this process to avoid setting any swirl marks into the glass, and you want the “footprint” of the grind to be generous - to help preserve flatness of both ground glass and plate glass.
- Opt for less pressure and longer time, to promote evenness.
- Stop rotating after about a minute to rinse the glass off and check it for evenness. You’ll notice that unground spots remain clear - and can bias your downward force to these areas on your next round of grinding.
- Don’t try to do a complete grind with one application of grit. Use two or three applications instead. Keep in mind that as you grind, the grit will get full of glass - and thus you should “refresh” the grit at least once (I prefer 3x) during the entire grinding process.
- Do make sure that each grind is long enough in duration to allow the grit to distribute evenly under the entire surface of the GG, and that any air bubbles have escaped.
- During your water rinses and final rinse, try to introduce a bit of water pressure to wash away any “gritty bits” which might otherwise tend to hang around. This is especially important for the final rinse.
- Finally, be very careful in attempting to clean the ground surface of the glass. My first preference is a plain warm water rinse. Second preference is a warm water with mild soap, followed by a warm water rinse. Third preference is for warm, soapy water applied first, then drag over this (without pressure) a sheet of lintless cloth or lens tissue. Only if none of the above works will I actually apply finger pressure.
- In any case, I always allow the GG to air dry after the final rinse. I’ve never had problems with drying spots…but if I did I’d opt to try using distilled water for my final rinse, and would only add anything like a wetting agent (and only then extremely diluted) as a last resort.
- If you plan to make a number of ground glass sheets, be sure to do periodic checks of the flatness of the sheet glass base piece (which can “crater” with lots of use over time). I use a metal straight edge for this purpose. To the extent that you can create even and gentle pressure, over an area of rotation considerably larger than the dimensions of the actual ground glass, will help to extend the useful life of the thicker plate glass base piece.
Ron, that is exactly the process and materials I use.
Tin Can
Many thanks John for these clarifications and practicalities. Indeed I didn't write about the grinding itself, only wrote a general introduction (written under the first picture where the clear glass is shown). Therefore your advice is most welcome. Where my approach differs from yours I will mentioned it in the following:
1. I'll place the glass that will be the ground glass focusing screen, on a layer of paper which is sprayed with water so that the glass stays at one position during grinding;
2. Different from your approach, my grinding tool (a thick piece of glass) lays on top and I will make circular strokes on the glas that will be the focusing screen - I think this is easier than your approach when grinding a large piece of glass and it involves less risk in breaking the focusing screen during the process;
3. My grinding powder is Silicon Carbide. I use different grades; F400 for very big screens and F600 for the smaller ones. Sometimes I use F400 for a first step and F600 for a final grinding;
4. I also use water to clean the ground glass focusing screen. Here in the Netherlands we have very clean drinking water from the tap which is adequate for cleaning the glass once and then dry with a normal towel. I have never seen gritty bits tending to hang around after cleansing the screen under the water tap - cleaning a screen is therefore afaik no problem at all;
5. I second your advise that it is better to make more strokes with less pressure to get an even surface;
6. When doing a smaller screen (4 x 5" or less), I found no refreshing of the grit needed - however when a second grinding is required I'll always take fresh grit.
Made my 1st 11x14 screen (after breaking 1) using these steps and I must say that the screen is quite amazing. Bright and easy to see very fine details. I used both 400 and 600 silicon carbide.
I just used Lapidary Pre-Polish, aluminum oxide, #591-021 from Lortone, Inc. to make an 8x10 ground glass. It turned out nicely.
“You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
― Alexander Den Heijer, Nothing You Don't Already Know
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