That's Amateur Telescope Maker
I guess you can blame Isaac Newton. He is the person that invented the reflecting telescope. There are telescopes built with lenses and a combination of lenses and mirrors too, but most home built instruments are Newtonian reflectors. Scientific American magazine is responsible for spreading the word on how to make your own objective mirror in the 1920's. At that time the Mount Wilson 100" telescope was the world's largest telescope and plans were just beginning to jell for the 200" telescope on Palomar mountain. Amateur astronomers itching for their own telescopes discovered how to build their own in the time of the great depression. Today you can buy a quality telescope at reasonable prices so building your own from scratch isn't mainstream anymore.
If you want a BIG telescope you might still build it yourself, though you'd probably buy the optics ready made. Making your own objective mirror isn't a difficult thing to do, but learning how isn't something you can do on a large mirror. By the time you've mastered the art making several smaller mirrors your cost in materials (and time) will probably exceed the cost of just buying a ready made mirror by enough to also pay for a good chunk of the rest of the telescope. The true MacGyver type would still rather make his or her own optics.
When I was in my late teens I tried to grind my own 6" mirror using a kit from Edmund Scientific. I never finished the mirror as the polishing was so messy that I gave up to keep peace with my mother. I did buy a complete kit of factory made optics from A. Jaegers and built a rather nice 6" Newtonian reflector. The scope was mounted on a 'turn on threads' pipe mount. I sold that scope when I finished college and moved to the Boston area. I'm kinda sorry I got rid of it now.
If you want a BIG telescope you might still build it yourself, though you'd probably buy the optics ready made. Making your own objective mirror isn't a difficult thing to do, but learning how isn't something you can do on a large mirror. By the time you've mastered the art making several smaller mirrors your cost in materials (and time) will probably exceed the cost of just buying a ready made mirror by enough to also pay for a good chunk of the rest of the telescope. The true MacGyver type would still rather make his or her own optics.
When I was in my late teens I tried to grind my own 6" mirror using a kit from Edmund Scientific. I never finished the mirror as the polishing was so messy that I gave up to keep peace with my mother. I did buy a complete kit of factory made optics from A. Jaegers and built a rather nice 6" Newtonian reflector. The scope was mounted on a 'turn on threads' pipe mount. I sold that scope when I finished college and moved to the Boston area. I'm kinda sorry I got rid of it now.
A 7" F7 3/4" thick Plate Glass Mirror
A few years ago a large cache of surplus plate glass became available. The glass was in the form of 2' square sheets piled in stacks on pallets. Most of the stuff was 3/4" thick, though there were some 7/8" thick pieces available too. One ATM type I met on the internet put in an order for several pieces and offered to get one for me. He was going to be in the Keys to go fishing was going to pass though my area on the way. So we met in person and he dropped off a sheet of glass for me. I figured out how to cut a circular piece of glass out of a larger sheet using my drill press. I built a circle cutter out of some plywood and sheet metal. Cut out a circle of plywood using a plunge router with a guide base, wrap a band of sheet metal around the circumference of the plywood disk, drill a hole in the middle of the disk to take a 1/2 carriage bolt, and chuck the bolt in the drill press. The sheet metal band is the cutter using some #80 carbo and water to do the cutting. A playdough dam holds the cutting sludge in place. I put an extension table with leveling feet on the drill press made from plywood and homosote and the glass sits on that. I adjusted the extension table leveling feet so the glass is square with the chuck in the drill press. I ran the drill press at its lowest speed (190 rpm). It took about 1/2 hour to cut each of two 7" disks out of the sheet glass. One disk is the mirror and the other is the tool. Today most ATM's make a tool out of dental plaster and ceramic tiles rather than waste a piece of glass. For a large mirror this makes sense, but for a mirror under 8" you might as well do it the traditional way.
It's a grind
To turn a glass disk into a telescope mirror requires grinding and polishing it to a concave surface and then coating that surface with a reflective metal film. The grinding is done using a tool and a series of abrasives. The rough curve is formed with #80 (or larger) carbo, and then the surface is smoothed with a progression of finer abrasives. Finally the surface is polished using a pitch covered tool (called a lap) using an optical grade polishing agent. During the final polishing the mirror is tested and the figure adjusted to be a perfect(!) parabola. If a full size tool is used the tool is placed face up on a work surface and the mirror is worked on top. This process causes the mirror to become concave and the tool convex. The process involves the use of long off centered strokes with the tool. A sub-diameter tool can also be used with the mirror face up on the work surface. The latter method is prefered for large mirrors, for small mirrors the full size tool is prefered. This is the method I used.
The work surface is usually the the top of a barrel or a drum that is weighted down with sand or water. This allows the worker to walk around the work while rotating the mirror (or tool). This rotation process helps produce a perfect figure of rotation (sphere). I built a stand out of wood that resembles a barrel. Eight pieces of 1x2 wood strips form a 'truss' tube that are attached to a plywood base and a plywood top work surface. The base is a 2' square piece of plywood, the top is an 18" circle of plywood. The top is varnished and covered with oil cloth (an old table cloth actually) to water proof it. The bottom is weighted down with heavy objects. Most people would use concrete blocks or bricks. I used about a dozen large transformers from some scrap UPS systems that were thrown out where I worked. (I was saving the transformers for use in low voltage power supplies).
At this point my mirror has been ground to an F7 (47" Focal Length) and I've fine ground it with #120 and #220 carbo. I'm just starting the #320 carbo now. After that it's on to 25, 15 and 9 micron AlOx abrasives. THEN we polish it.
UPDATE:
I finished grinding with #320 carbo. In the middle of this I cut some 'channels' into the glass of the tool to help break up suction during the fine grinding. I'm now working on the 25 micron AlOx. With this stuff it's better to mix the abrasive powder with water in a squeeze bottle rather than apply the powder dry to the mirror. In fact, this method would well with the #320 too as at that size the abrasive is almost a powder rather than a sand. The 25 micron and smaller stuff IS a powder, no resembence to sand at all. I've been alternating mirror on top with tool on top grinding, but at this point I'll be sticking with tool on top. The focal length is around 46-47" at this point and grinding TOT should increase it slightly. My goal was around 49" but a few inches either way won't matter.
The work surface is usually the the top of a barrel or a drum that is weighted down with sand or water. This allows the worker to walk around the work while rotating the mirror (or tool). This rotation process helps produce a perfect figure of rotation (sphere). I built a stand out of wood that resembles a barrel. Eight pieces of 1x2 wood strips form a 'truss' tube that are attached to a plywood base and a plywood top work surface. The base is a 2' square piece of plywood, the top is an 18" circle of plywood. The top is varnished and covered with oil cloth (an old table cloth actually) to water proof it. The bottom is weighted down with heavy objects. Most people would use concrete blocks or bricks. I used about a dozen large transformers from some scrap UPS systems that were thrown out where I worked. (I was saving the transformers for use in low voltage power supplies).
At this point my mirror has been ground to an F7 (47" Focal Length) and I've fine ground it with #120 and #220 carbo. I'm just starting the #320 carbo now. After that it's on to 25, 15 and 9 micron AlOx abrasives. THEN we polish it.
UPDATE:
I finished grinding with #320 carbo. In the middle of this I cut some 'channels' into the glass of the tool to help break up suction during the fine grinding. I'm now working on the 25 micron AlOx. With this stuff it's better to mix the abrasive powder with water in a squeeze bottle rather than apply the powder dry to the mirror. In fact, this method would well with the #320 too as at that size the abrasive is almost a powder rather than a sand. The 25 micron and smaller stuff IS a powder, no resembence to sand at all. I've been alternating mirror on top with tool on top grinding, but at this point I'll be sticking with tool on top. The focal length is around 46-47" at this point and grinding TOT should increase it slightly. My goal was around 49" but a few inches either way won't matter.
The Dobsonian
The telescope will be a 'Dobsonian' mount type, so called because it was invented by John Dobson. The Dobsonian design makes it easy to build a large telescope at reasonable cost. Instruments of this type have been constructed in sizes of 42" and larger by ATMs. I haven't decided whether to us a solid tube such as a 'sonotube' or use a truss tube construction. The former makes more sense in an urban environment as it shields the eyepiece and main mirror from stray light, but a truss tube will balance closer to the bottom of the scope and make for a more portable instrument as it can be broken down for transport. I'd also like to put some stepping motors in the mount so the scope can track objects with computer control.