A chain whip is a bike tool. Here's how to make one.
Step 1: Find the Parts
- You need a sturdy round bar or flat bar. I used a smooth round bar a got from the rails of an old printer. The longer you use the more leverage you'll get. About 12" will work fine.
- Some old bike chain. 12" or so will work fine. I find that the farther you wrap around the gear the better the chain holds.
- A welder or POSSIBLY you could put a hose clamp around the end and the middle to secure it. If using a flat bar, drill and bolt it.
Step 2: Assembly
Pictured below is a commercially made chain whip. I find that my method works fine too. But 5-10 chain lengths over 3"-4" should work fine for the "secured" portion. Simply leave the rest unattached.
http://bicycletutor.com/replace-cassette-cluster/ shows a chain whip in action.