My 6" f8 scope
Posted 20 January 2013 - 01:58 PM
I joined the friendly guys at ScopeX this Saturday afternoon. In no time I had a 6" blank and a matching glass tool in my hand!
The disks seems to be cast. 1 inch thick. I searched for one with minimal bubbles and started to level a side of both the tool and the blank on a metal disk and some grit. Also did the edges of both.
I was shown how to do a center over center stroke, about 1 third over, issued with some 80 grit and encouraged to start grinding.
I have brought the lot home, built myself a grinding table and am now hogging out my first mirror. Measured it tonight (after 5 hours of grinding) and I think my Sagitta is just over 0.5 mm. I need 1.1 for a f8 scope, thus still quite a bit of glass to remove! My measurement was with a straight edge and some feeler gauges, thus not very accurate.
I think I found myself some good coaches. They have all the tools neede to measure and figure a good mirror. Johan, the guy who is taking me under his wing is busy with a monster disk. Something like 24"!
Many people are in various stages of telescope making. Some were done, others were polishing and others like me were issued with some glass.
I must say, it has only been the first 5 hours of a very long journey, but I am finding it quite addictive!
Posted 20 January 2013 - 02:40 PM
Posted 22 January 2013 - 04:08 AM
Bwa ha ha, another soul for ATM
Posted 22 January 2013 - 10:11 AM
Posted 22 January 2013 - 10:48 PM
Posted 23 January 2013 - 03:01 AM
Posted 23 January 2013 - 02:11 PM
I am measuring with a straight edge and a vernier. Will go off to ScopeX on Saturday. There I can get a good measurement.
Hope to move on to 120 grit! Progress!!!
Posted 26 January 2013 - 01:00 PM
Posted 26 January 2013 - 02:02 PM
Posted 28 January 2013 - 01:28 PM
Johan had a theory that I went too quick in rough grinding. He recommended a bit more time on 120 to ensure the rest goes quick.
I am really happy with the surface now. Will start 240 tomorrow. Hopefully the hour and a half per grit s true. I have stock all the way down to 400.
I am so excited about this project.
Posted 28 January 2013 - 04:21 PM
Using the right amount of pressure is important. Too little, and it is slow work. Put significant weight on it, and change grit often, reduce pressure towards the end of the grit grade.
If it seems that you're using a lot of grit, scoop it up, wash it, and reuse.
All this will become second nature on your 3rd or 7th mirror.
Posted 28 January 2013 - 07:36 PM
Remember to keep the outside edge beveled. As you grind your edge will sharpen and you can quickly lose the bevel you made in the beginning. It is worth the time you spend keeping your bevel in shape.
A sharp edge will crack, chip or spall. Fixing that takes a long time.