10" f/4.7 cellular mirror
Posted: Sat Jul 24, 2021 7:26 pm
I came up with the idea of buying a cellular 10" blank from BVCTek and making it into a mirror/travel scope. I probably need to get better at making mirrors if there is any hope of me going above a 30", and it's cheaper than paying an optician, so I will be grinding this blank into a mirror. My shop is also finally clean and organized enough that with some precautions I feel it's actually possible to make a mirror in there. This will be my third mirror I've done, after a 6" f/ 8 and my 6" f/ 4.3 (which still needs to go back into a scope).
I've come up with a fairly reasonable (I think) design for the scope, which I calculate will result in a total weight of a bit under 15 pounds. It's more or less a shameless copy of Adam Long's excellent build but I plan on a smaller secondary, smaller focuser (1.25" only), carbon fiber poles and of course the cellular BVC mirror (which weighs only 3 pounds) shaves off quite a bit of weight. The idea is that I could keep this scope fully assembled and walk outside carrying it in one hand, or stick it in a backpack and fly with it with little in the way of hassle. Theoretically this could probably be scaled up to a 12-incher if it all works out, and I suppose if I found myself travelling frequently enough I would do so, but I think 10" is better as a scope that's more of a grab n' go - and it's a little cheaper and easier anyway.
Yesterday I finally made a tile tool and started rough grinding. I had to start with #80 due to some problematic low areas on the mirror. These seem to be an artifact of the molding process. One particularly bad pencil-eraser sized spot near the edge will not grind out and from the side is visibly "dented". It will go under a clip in the cell, so I'm not really concerned. I've been using normal strokes and got the tool in good contact after about 2 hours with #80. After an hour today with #120 I'm ready to move on to #220.
I'm working the whole thing on a folding square Kreg workbench in my garage covered with tissue paper that I can dispose of between grits. Crude but gets the job done.
I've come up with a fairly reasonable (I think) design for the scope, which I calculate will result in a total weight of a bit under 15 pounds. It's more or less a shameless copy of Adam Long's excellent build but I plan on a smaller secondary, smaller focuser (1.25" only), carbon fiber poles and of course the cellular BVC mirror (which weighs only 3 pounds) shaves off quite a bit of weight. The idea is that I could keep this scope fully assembled and walk outside carrying it in one hand, or stick it in a backpack and fly with it with little in the way of hassle. Theoretically this could probably be scaled up to a 12-incher if it all works out, and I suppose if I found myself travelling frequently enough I would do so, but I think 10" is better as a scope that's more of a grab n' go - and it's a little cheaper and easier anyway.
Yesterday I finally made a tile tool and started rough grinding. I had to start with #80 due to some problematic low areas on the mirror. These seem to be an artifact of the molding process. One particularly bad pencil-eraser sized spot near the edge will not grind out and from the side is visibly "dented". It will go under a clip in the cell, so I'm not really concerned. I've been using normal strokes and got the tool in good contact after about 2 hours with #80. After an hour today with #120 I'm ready to move on to #220.
I'm working the whole thing on a folding square Kreg workbench in my garage covered with tissue paper that I can dispose of between grits. Crude but gets the job done.