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Thread: Building a dob

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    Default Building a dob



    is it conceivable to build a large Dobson-style telescope (20"-25" range) for far less than buying one would cost? To me it seems the only major price factor is the mirror, and rest can be made of inexpensive wood and aluminum or other lightweight materials.

    How expensive are mirrors of that size? Is it possible to piece small hexagonal mirrors together, or does that only work for very large scales? Can one, with some practice on smaller mirrors, accurately make a 25" mirror by hand?

    I'm not necessarily planning on trying to make my own telescope, but it's been something I've thought about for a long time. With 20" dobs costing $8000+ online, it seems like you should be able to make your own at a fraction of the cost, if you have the tool and the patience.

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    Default

    The first DOB were all homemade, including the mirror ... surplus ship port hole glass was used as mirror blanks. A good book on the subject ... the bible so to speak... is "The Dobsonian Telescope, A practical Manual for Building Large Aperture Telescopes" by Kriege and Berry.

    The mirror is the big cost item. A 20 inch (510 mm) mirror cost around $4000.

    Some people do make large mirrors but I suspect that they had plenty of practice on smaller ones first.
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    Default

    Quote Originally Posted by sxinias View Post
    The first DOB were all homemade, including the mirror ... surplus ship port hole glass was used as mirror blanks. A good book on the subject ... the bible so to speak... is "The Dobsonian Telescope, A practical Manual for Building Large Aperture Telescopes" by Kriege and Berry.

    The mirror is the big cost item. A 20 inch (510 mm) mirror cost around $4000.

    Some people do make large mirrors but I suspect that they had plenty of practice on smaller ones first.
    Why is the mirror so expensive? Are the raw materials expensive or the time it takes to grind one?

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    Default

    if you grind your own mirror, it will only cost you about $2k. look up "telescope mirror blanks" and buy yourself a pyrex kit, take some classes, and boom- 20" telescope mirror with optics 2-6x as good as you can buy.
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    Default

    Actually you can grind your own 20 inch mirror for less than 300-500 us dollars.
    you can make it out of either 1 inch or 1.5 inch float plate glass, get your grinding grits from willmann bell or gotgrit, you can ask other amateur mirror makers how much grit you will need and you can grind out the curve also knowen as "hogging the mirror" with diamond cutting blades, see my post on the diamond trail also my youtube videos under zi6film, using diamond cutting blades is more cost effective than using grit for the first stage, i could go strait to 220 grit after hogging out ....anyway enough talk from me this forum has some of the brightest minds of the 21 century so you will have all there expertise on hand so go find that slab of inch float plate cut it into a circle and make a 20 inch mirror !!

    PS my first mirror was 14 inches and it turned out good !!

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