just started pushing the glass

Hi guys.
I just started grinding 203mm f/6 mirror. After over two hours I reached sagita depth of 1.194 mm (target is 2.1 mm)- measured by using feeler gauge and metal ruler.

When I look at the mirror surface I can see 'grinded circle' - it starts around 1 inch from mirror edge. (attached picture) Is it correct? I mean, isn't it too far from the edge? Moreover this 'grinded circle' is moved a little bit towards one edge (it's center is placed correctly though). What I am doing wrong?

thanks

Attached Image:

Marcin, are you working center-over-center or tangentially? This is the pattern one would expect to see if you're working tangentially. If you are, now is probably the time to begin working center-over-center. Use 1/3 - 1/2 diameter strokes until the curve reaches the edge and the sagitta is correct. When that happens, go to 1/3 strokes for a few wets to get the surfaces into decent contact before going to fine grinding. Longer strokes will likely give you a slightly hyperboloidal mirror and oblate spheroidal tool, so you want to get the two disks into reasonable contact before moving to a finer grit size. Once the surfaces are in decent contact (it won't be perfect with #80 grit), use the reflection test as others have described to determine the focal length and get it close before going to #120. Doesn't have to be exact, but it's more and more difficult to adjust the focal length as you go to finer and finer grits.

Keep us posted.

Doug