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Querry on grinding a 12.5" mirror

Started by BABOafrica, 06/24/2012 11:13PM
Posted 06/24/2012 11:13PM Opening Post
Update on progress:

I have almost reached the sagitta of 3mm using #100 grit. There is no noticeable astigmatism, at least not by rough measure. I say this because I can slide a series of drill bits in various directions under a straight edge and each size pushes out the same distance no matter which direction I choose. So, I feel that things are going pretty well.

BTW, I made a new tool using small pieces of 4mm glass. This works quite well. The grinding proceeds very smoothly.

The one thing that I'm not sure of this: there's still a 5mm ring all around the edge where no grinding (or at least very little) has taken place and so the edge is still flat. Otherwise, there seems to be a nice smooth curve from center out towards the edge.

Is this the normal thing?

Clears,
Joe

In lumine tuo videbimus lumen.

8O Home-made 10” Dob / Home-made 4” refractor

EPs: Konig 32mm (1.25") / Zhumell WF 30mm (2") / Nagler 13mm T1 / Orion Sirius Plossls 25 & 10mm / Zhumell Plossl 9 mm / Meade MA 9mm
Posted 06/25/2012 12:36PM #1
Sounds like reasonable progress so far. It takes a long time to push the curve right out to the edge because at this point you have to remove a layer of glass from the whole surface. As long as the resistance of the tool is smooth, I wouldn't be concerned with problems at this stage.

dan
Posted 06/27/2012 01:17AM #2
Here's some pictures of the mirror blank and the tool.

Clears,
Joe

Attached Image:

BABOafrica's attachment for post 144593

In lumine tuo videbimus lumen.

8O Home-made 10” Dob / Home-made 4” refractor

EPs: Konig 32mm (1.25") / Zhumell WF 30mm (2") / Nagler 13mm T1 / Orion Sirius Plossls 25 & 10mm / Zhumell Plossl 9 mm / Meade MA 9mm