These will not only give you a much shorter radius, but you can build any configuration you desire by soldering pieces of pipe between them. If you are REALLY intent on building your own cooler, might I suggest a trip to your local heating and air conditioning supply store.(No you won't find these at Home Depot) There you can purchase 180 degree bends. Not to mention the fact that this tool is quite expensive.

You could also acquire a 'Rigid' tubing bender that will allow you to make some professional looking bends but, the bending radius will be quite large and the scrap you will make trying to learn how to use the thing seems hardly worth it to me.

Sure you could get a 'bending spring' and bend it but, it will still look kind of cheesy when you are through. Unless you have some really radical radiator design in mind, bending copper really isn't worth the effort.