A bike's moving parts will need tender loving care. For years I've used single speed bikes to avoid extra upkeep and simplify my toolkit. I've changed over to gears and have needed extra cleaning, parts and tools. If you ever remove the gears on the rear wheel (AKA cassette more generally known as a cogset) you will need a Chain Whip/Sprocket Remover.

If you don't know why you would want a chain whip you can watch a 3 minute YouTube on its use. There are also great instructables on the subject.

Step 1: Why Would I Make One?

You can buy them at any bike store for about $20. I have a tight budget ... actually I'm cheap. Either way I like used tools. A 'real' chain whip is tricky to come by as there aren't many uses for one. There are legit DIY solutions out there but I'm too lazy (they also ask for other tools I don't have). I've written the cheapest/fastest/easiest solution I know of.

Step 2: You Will Need: Screws/Driver

These were all items around my garage. Your resources may vary. Clearly this won't need to be too particular but you want to make sure the screws can fit between the chain. Acquire a:

Screwdriver
Screws - 1" to 1.5" long

Step 3: You Will Need: Wood

Any board will do. The longer the plank the better the leverage you will have. The thinner boards are easier to work with. If I had to get specific I'd suggest:

1" x 3" x 8" seemed

Step 4: You Will Need: Bike Chain

This might be less available but easy to get. You might have one in the garage, find one on the road or buy a wrecked $5 bike for parts. I would recommend:

6" of bike chain

My house has many bikes, projects and wrecks so I am well stocked. I found the perfect length on the side of the road. It was super rusty but instructables has many rust removal solutions. If you need to unlink or break the chain you can:

Get an official 'chain tool' to remove a pin
Use a hammer, nail (or pin) and pliers to remove a pin
Cut it with a hack saw?

Step 5: Attach Chain to Board

Screw the chain onto the board so the links hangs over the corner 3 to 4 inches. I secured the chain in three locations. If you're on a budget you could get away with one or two screws I guess? Buck up and go with three to make life easier down the road.