how does a retractable ink pen work?

Answer 1

If you're talking about the typically cheap pen with a button on the top that you click to make the pen come out and click again to make it retract, then I say they're pretty cool mechanically. I recommend you find one and take it apart. Alot of this sort of pen are given away as promotional items, so they're shouldn't be any cost associated with the pen. Inside, you'll find a spring which keeps the pen cartridge retracted, and at the other end, a set of concentric cogs. One of the cogs has sets of teeth at two different levels -- one for pen retracted and one for pen extended. There are also some bits in the barrel of the pen that you can't easily see, if I'm not mistaken.

But seriously, it shouldn't be hard to find this type of pen in just about anyone's junk drawer, so I strongly suggest you take one apart. They're typically pretty easy to put back together.

Answer 2

The only retractable ink pens i know are antique ones. The nib retracts by turning the 'knob' at the end of the barrel. You fill them using an eyedropper. They invariably leak and are fairly difficult to repair.

Answer 3

Gee, why don't you take a couple of bucks down to your local office depot and get one, then unscrew the thing and look at it yourself.