Re: how does a can opener work

I am going to describe the hand can opener.  An electric can opener works 
in much the same way, except it is driven by an electric motor.

Can openers work because cans have been somewhat standardized as far as the 
height of the lip at the edge, etc.  If you want to see how long it took to 
invent a good can opener, visit the web site below.

Inventor of can opener
 http://sciencenet.oit.net/database/Technology/9810/t00276d.html


The opening process starts by applying a pressure to close the jaws of the 
opener around the top and bottom lip of the can.  The serrated wheel grips 
the lower edge of the can lip and the upper jaw pierces the can lid just 
inside the lip.  You can think of the opener as a large pair of pliers at 
this point, with a sharp point on one edge of the pliers.  Once pierced, 
the handle of the opener is turned to drive the serrated wheel.  As long as 
you hold the handle tight enough to overcome the force of the metal cutting 
action, the serrated wheel moves the cutter blade through the can top.  
This is not unlike a plow being pulled through a field.  It takes a lot of 
force to hold the cutter down and pull it through the metal.  A metal 
cutting lathe cuts metal in the same manner, dragging a sharp tool through 
the metal while it spins by at high speed.  The cutting blade has to be 
stronger than the metal it is cutting so as to not wear out too fast.  
Metal cans are actually pretty thin and weak.  You can practically cut them 
with a pair of scissors when they are just thin sheet metal laid out flat.

There is usually enough leverage between the handle of the can opener and 
the cutting blade that hand pressure is enough to keep the blade in contact 
with the can and the serrated wheel moving.  Sometimes, if the lip of the 
can is slightly higher than normal or the blade is dull, you have to really 
clamp down with your hands to keep the blade cutting.  If the serrated 
wheel is worn, it might slip and not have enough frictional grip to drive 
the cutting blade forward.

Electric can openers have the same piercing action and a motor to drive the 
wheel.  The clamping action is released when a switch senses the top of the 
can falling away from the cutter.