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Hi Cristian,
I hope to make a nice 10" mirror in the next few years so I need lots of practice! A nice cassegrain like what you are going to do would be tops! I think I stick with a newt. Doing the convex secondary would be beyond me and drilling a hole through the primary would be rather scarey. Maybe oneday.
Well I had a go at figuring. Overall about 4 goes at 10-12 min each. After the first 2 goes the shape started going the right way but so did a lump in the middle and a bit of a TDE . Soo I tried something out of Texereau`s book with tool on top working just around the edge. I slipped twice and put a few scratches across the lap but luckily not the mirror. No damage thank goddness!! I had to scratch my head a bit as to the bumo in the middle? After looking at the normal parabolizing stroke, I worked out that the bump was exactly the same size as the distance from the cente of the mirror stopped where the www stroke finished at the edge. Next 2 sessions I took the centre all the way to the edge and it worked. Bump in the middle just about invisible and mirror seems to have smoothed out real well. It looks very close to my printed matched ronchi images I printed the other day. I will have to fix my tester a little more and get it running smoother and do some measurents. Let me know if you think I am close (you can see those defraction rings real easy in this shot). I still have a small TDE so I might bevel it out like you suggest? What is the best way to rebevel? I will post some knife edge pics in the next few days.
Best regards Gary
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