10" f/4.7 cellular mirror

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Augustus
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10" f/4.7 cellular mirror

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Post by Augustus »


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.
120grit.jpeg
Zane Landers
Member: ASNH, BMAS, LHAAC, MHAA, RAC, WAA, WAS
Featured in TIME, National Geographic, The Guardian, Sky & Telescope
Scopes: 24" f/3.5 & 14.7" f/2.9 Dobs w/Nova optics, Orion XT6i, Zhumell Z114, Sears 6335
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Makuser United States of America
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Re: 10" f/4.7 cellular mirror

#2

Post by Makuser »


Hello Zane. This looks like a pretty nice project. I remember back in the early 60's, many folks used to go to the Adler Planetarium in Chicago and grind their 6" mirrors every Saturday. Thanks for your report and picture Zane, and keep us posted on your progress.
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NGC 1365 Australia
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Re: 10" f/4.7 cellular mirror

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Post by NGC 1365 »


Looking forward to your progress, thanks for sharing Zane.
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Augustus
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Re: 10" f/4.7 cellular mirror

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Post by Augustus »


Thanks guys!
Zane Landers
Member: ASNH, BMAS, LHAAC, MHAA, RAC, WAA, WAS
Featured in TIME, National Geographic, The Guardian, Sky & Telescope
Scopes: 24" f/3.5 & 14.7" f/2.9 Dobs w/Nova optics, Orion XT6i, Zhumell Z114, Sears 6335
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Re: 10" f/4.7 cellular mirror

#5

Post by Augustus »


So this thing is like butter - #120 and #220 have each taken little more than an hour. I am going to try to get to polishing by tomorrow night. Might throw it in a structure for Stellafane at this rate
Zane Landers
Member: ASNH, BMAS, LHAAC, MHAA, RAC, WAA, WAS
Featured in TIME, National Geographic, The Guardian, Sky & Telescope
Scopes: 24" f/3.5 & 14.7" f/2.9 Dobs w/Nova optics, Orion XT6i, Zhumell Z114, Sears 6335
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