Preparing a 14" mirror for the polishing stage

[alanlippert]

These are the steps to polish a mirror - the technique is specifically for mirror on top method. The reason for mirror on top is to prevent astigmatism, which is common for thin mirrors. This is a 14.1" quartz mirror that is .8" thick, which is nearly an 18:1 thickness ratio. First step is heating the mirror in preparation for the net press on the polishing tool. The net press creates small channels in the tool for a better polish. The pictures show weights on the mirror to press it to the tool for a period of about 15 minutes. Next a metal plate is fused to the back of the mirror with pitch material. This allows the mirror to be connect to a control arm that can be pushed across the turn-table the tool spins on during polishing. As of today, the mirror is polishing out nicely, but has been slow to polish out on very far edge. The figure is slightly oblate and getting closer to spherical. Once polished out and spherical then the real fun of figuring can begin. I could be as close to a week away from figuring baring any surprises.

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[Dragan]

Great post Alan!

Keep us posted on the 14" progress!

You should start a thread telling everyone about the trials and tribulations making your 16" mirror in that shop.

And then the story behind first light with that telescope!

[alanlippert]

As a follow-up, I wanted to mention Dan Joyce, who I have ground 4 mirrors with over the past couple of years. A 6" f/5.3, 16" f/5, 8" f/4.6, and now the 14" f/4.6. Dan is a legend in the art of mirror making and often brings photos to the optical shop from Don Parker, who images with a telescope featuring a Joyce mirror - specifically a 16" f/6 specimen. My favorite set of pictures are a direct comparison between Parker's images of Mars in 2003 with the Hubble Space Telescope. The detail seen in the Parker Photos is startling and true testament to what Quality Newtonian Optics can do.

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