If you've ever done any wood working you know that you start with the larger tools like saws and then work towards scrapers and finer tools like sand paper with the end result being a beautiful smooth finished product. Grinding telescope mirrors follows much the same process.
You'll start with a course grit that is used to remove enough glass from the mirror to produce the desired concave shape. The course grit gets left behind and finer and finer grit is used to remove the pits and polish the mirror to a high gloss.
You need to start with a mirror blank which is just a thick slab of glass. Consider buying a high quality Pyrex blank. You can get this from one of the many online telescope suppliers. You can use other types of glass but it can be hard to work with because the temperature changes cause it to expand and contract. Pyrex gives you a quality mirror without the trickiness of scavenged glass.
There aren't a lot of tools needed to make your mirror. In fact it's more like a tool rather than tools that you will need. Your grinding tool can be as simple as another glass blank although this is a rather expensive tool.
Instead you can purchase a cement or plaster tool that is covered with tile. The tiles are very inexpensive, the grind effective, and the lens produced quality. There are many sites online that will lead you through the grinding steps. There are several different methods so choose the one that best suits you.
The instructions may seem a bit overwhelming at first but the process isn't really that bad. The biggest requirement is patience. You need to take your time. Remember with a telescope lens you get what you put into it.
The best place to do your grinding is in a room that has a nice constant temperature, and 200 pounds of sand in a huge drum. But not everyone has the perfect scenario. Not to worry you can get away with just a simple grinding board.
A grinding board is just a piece of wood that has cleats screwed into it. These cleats hold the mirror so it doesn't' slide around. It's not that difficult to make.
Now to be fair you might consider purchasing your telescope mirror. There are all kinds of quality mirrors made by manufacturers like Meade, Celestial, Celestron, Vixon, Skywatchers, and Quester. So before you decide to take the time to grind your own telescope mirror do some searching online and discover what's available and the prices.
One great place to buy telescope mirrors at a terrific price is eBay. Often you'll find some great deals! But use a bit of caution. A mirror needs professional packaging if it's going to be shipped and you want to make sure that the seller has the necessary skills.
The larger the mirror you are planning to grind the more risk of error. And of course the larger the mirror the larger the piece of Pyrex you need to buy and the more it costs. So a good way to start is like with any other skill. Start small and then move up. So start by grinding a 4" or 6" mirror. That will give you the hang of it.
Grinding telescope mirrors is certainly a skill that's worth having. What you need to decide is whether it's easier to buy or grind your mirror. Do your research!