Originally Posted by
FBinNY
If learning is your objective, buying new bikes is an expensive way to go about it. See if there's a local bike Co-op, or a charity that collects and refurbishes bikes for poor kids. Or buy garage sale bikes, fix them up, and give them away or save them for a Christmas toy drive. I can think of no better way to celebrate the spirit of Christmas than to give a bike to a child who otherwise wouldn't have one.
You can also do your own thing by buying used bikes, fixing them up and selling them at low cost to people who can use them for basic transit. In many cities, you can find locations where these people gather for day work every morning.
I would heartily second the recommendation to look for a bike co-op or other source of in-person support, but seek out someone who will help you understand the
why of what you are doing rather than just how to make an adjustment. You
must understand how a component works and interacts with other parts, the rider and the environment if you are going to "learn a lot more about bikes."
In my experience putting together a bike is a costly way to learn, and not primarily in terms of money. It takes a lot of time to acquire, disassemble, cull out parts and put together bikes, and you can do so without ever finding the most efficient or even the proper way to do procedures. I would also caution you against giving away bikes until you are sure you know how to prepare one safely. Trial and error is mostly error, and "if I make a mistake at least I learned form it" is one of the most illogical concepts I have heard. If one makes a mistake that covers only know one of innumerable ways to be wrong. One learns from a mistake
only when the correct solution is the next step, whether presented by someone else or by seeking out accurate information.
What bike you work on next is irrelevent. What's important is that you develop your knowledge, observation and problem-solving skills. To start on your own, try learning everything you can about one component, such as a derailleur. Start by moving it in every direction, with your hand, pulling on the cable and using the lever, what it looks like as it moves, seeing how it accomplishes what it does, what allows it to move and what confines its movement. Then look at books, videos, online tutorials, and technical information about the part, installation and repair procedures. Think about why the procedures work in light of what you observed earlier. Extend that to the things the derailleur interacts with - the chain, freewheel/cassette and cable/levers. Think about how the interaction between parts in a system affects each one.
The reason I suggest the above is that once you do so with a few components (which in this case are part of the drive train
system) it should be more natural to approach your task as a careful, knowledgable observer, rather than a simple turner-of-screws. Most "repairs" - that is, working on something that is not Park Tool new and clean, depend mostly on analysis, knowledge and observation, with perhaps 10% comprising action. As the old plumber joke goes: "It's $10 for tapping the pipe to fix it and $200 for knowing where to tap."