Grinding of a 6" f/8 Mirror


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To make a telescope mirror, we start with a clear piece of glass and grind a curve into it. Since this mirror was made for the Boston ATM CLub (ATMoB), I had the opportunity to use a cast iron tool with channels cut into it. The tool was an 8" diameter with 3/4" tiles with a radius of curvature of 96" (approximately). Thus a mirror made with this tool will have a focal length of 48".

 

This tool was used by me to make an 8" f/6 before I began this project, and it went so well, I decided to make a 6" f/8.

Below is a photo of the 6" mirror on top of the tool.

 

 

I use plastic spoons to sprink grit on the mirror. For each stage of this project, I used about 1/2 teaspoon per 'charge'. When the grit sound was reduced and it sounded used up, I added another 'charge'. These are called 'wets'. Every 3-4 wets I wash off old grit and pulverized glass from the tool and mirror, to keep the process going fast.

 

The entire mirror was ground out and polished in under 4 hours of time, including taking the photos and washing up.

 

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