plastic ground glass substitute

I need a 16X20 ground glass for a camera I am building. I prefer plastic for its durability, but I want quality equal to fine ground glass. I am willing to make my own. Has anyone any experience doing this that they would like to share?

The problem with plastic of that size is maintaining flatness. Plastic thick enough to remain dead flat won't be light in weight, or cheap to buy. Due to its softness, plastic is also quite difficult to grind without getting scratch lines across it.

 

I really think glass is your best bet. It can be fairly easily vapour or sand-blasted to a good finish, or even hand paste-ground if you have the patience.

The problem with plastic of that size is maintaining flatness. Plastic thick enough to remain dead flat won't be light in weight, or cheap to buy. Due to its softness, plastic is also quite difficult to grind without getting scratch lines across it.

 

I really think glass is your best bet. It can be fairly easily vapour or sand-blasted to a good finish, or even hand paste-ground if you have the patience.

That is a good point, Joe. I am willing to work with glass. So, does anyone have any experience with grinding their own glass they would like to share?

I've only used a wet-blasting cabinet to make a 5"x4" GG screen. It's fairly easy once you get used to the thick rubber gauntlets and can keep the nozzle moving smoothly and evenly. Basically it's down to trial and error on scrap bits of glass, since you can't see what the "grind" is like until all the blasting grit is washed off and the surface dried.

 

You also need a tough coating to protect the shiny side of the glass. A vapour-blaster goes through masking tape in milliseconds!

That is a good point, Joe. I am willing to work with glass. So, does anyone have any experience with grinding their own glass they would like to share?

I've only used a wet-blasting cabinet to make a 5"x4" GG screen. It's fairly easy once you get used to the thick rubber gauntlets and can keep the nozzle moving smoothly and evenly. Basically it's down to trial and error on scrap bits of glass, since you can't see what the "grind" is like until all the blasting grit is washed off and the surface dried.

 

You also need a tough coating to protect the shiny side of the glass. A vapour-blaster goes through masking tape in milliseconds!

Vapor blasting is new to me, but interesting.

It's called vapour-blasting, but it's actually a high pressure mixture of carborundum or silica grit, and water. Messy but effective. It has to be contained in an airtight blasting cabinet because it can easily take your skin clean off.

 

Look for small engineering works or places that prepare items for painting or surface coating. An operative might do the job for you for a small payment. No guarantee it'll be done to your liking though.

I need a 16X20 ground glass for a camera I am building. I prefer plastic for its durability, but I want quality equal to fine ground glass. I am willing to make my own. Has anyone any experience doing this that they would like to share?

Look up suppliers of scientific float glass that are near you and tell them what size you need. Also ask if they can supply one side ground and, if not, who they might recommend to do it.

Way back in high school I ground a reflecting telescope mirror. A similar, but way easier, technique may be used to grind one side of a glass plate into a "ground glass" screen. Use a medium or fine silicon carbide abrasive plus water slurry between the glass plate and a smaller and thicker glass plate and, with pressure, push the smaller plate in circular motions around the larger plate. It should take only ten or twenty minutes to grind a suitable "ground glass" (as opposed to grinding and polishing and testing a parabolic telescope mirror, which involved weeks of work and more patience than a modern high school student would tolerate). Silicon carbide abrasive may be found at willbell.com (back in the old days, Edmund Scientific was the go-to supplier).

Look up suppliers of scientific float glass that are near you and tell them what size you need. Also ask if they can supply one side ground and, if not, who they might recommend to do it.

Thank you, Bob.

Way back in high school I ground a reflecting telescope mirror. A similar, but way easier, technique may be used to grind one side of a glass plate into a "ground glass" screen. Use a medium or fine silicon carbide abrasive plus water slurry between the glass plate and a smaller and thicker glass plate and, with pressure, push the smaller plate in circular motions around the larger plate. It should take only ten or twenty minutes to grind a suitable "ground glass" (as opposed to grinding and polishing and testing a parabolic telescope mirror, which involved weeks of work and more patience than a modern high school student would tolerate). Silicon carbide abrasive may be found at willbell.com (back in the old days, Edmund Scientific was the go-to supplier).

Thank you, Glenn. I am taking mental notes on everyone's suggestions. I will not be rushing into this project. I probably will be hand grinding my GG. I like the simplicity of the process. I even have some powdered abrasives on hand.

Optical flat grinding using three blanks per making your own telescope instructions seems like overkill. I found this article by Dick Dokas describing grinding an 8x10 view camera glass. The technique with the grits he recommends seems very straight forward.

 

Dokas Photos – How To Ground Your Own Glass

Optical flat grinding using three blanks per making your own telescope instructions seems like overkill. I found this article by Dick Dokas describing grinding an 8x10 view camera glass. The technique with the grits he recommends seems very straight forward.

 

Dokas Photos – How To Ground Your Own Glass

Yes, that is the best method and instructions I have found yet. He said it would take about 2 hours to do the job using 5 micron AL oxide.

Your 16x20 is 4x the surface area, so grinding will take a day. Good luck with your project!