# Electric tin openers

First of all, I’ve checked on Google and Ask Jeeves and howstuffworks.com, but can’t seem to find the answer to this puzzling situation…

After losing the use of my dominant hand (for the most part) I’ve had to switch from hand-held tin openers to electric tin openers. They are rather fun and handy really.

But… how the bl@@dy heck do they know when to stop opening the tin? No matter what size the tin is it does a complete circuit and stops just after opening.

I’ve even had the hubby open it partly then put it in the electric opener… and it still goes around and opens it completely…

How dey do dat???

They have micro-chips that figure out C = pd (p=3.14 d=diameter).

It may help if you explained to everyone that a tin opener is also known in the colonies as a can opener.

I don’t follow the sense in this: They have micro-chips that figure out C = pd (p=3.14 d=diameter). It simply shifts the question to how has the can opener determined the diameter of the can?

My guess is that there is a microswitch connected to the cutting wheel. The electric openers I’ve seen have spring-loaded cutting wheels. They can rise in their housings a few millimeters, and they are automatically pushed up when the can is loaded. When the wheel comes around to the beginning of the cut, it falls back down into the gap there and turns the microswitch off.

I’d have to agree with the last post; there’s most likely a circuit made/broken by pressure on the cutting wheel. We’ve had an electric can openeer since before I was born, and it’s nowhere’s near sophisticated enough to know how to calculate the circumference of a can and quit cutting .

And since they also happily open cuboid tins (e.g. corned beef), that pi business wouldn’t be much use.

I’m the hubby mentioned in the OP and I thought the same as Gary T and mmmiiikkkeee, but I’ve experimented by using a normal can opener to go half-way around the can then putting it in the electric one. It still goes all the way around.

Perhaps your hand-operated opener leaves a less clean edge, thus still giving the electric one something to push against. Try putting the same can through twice.

Hey, it didn’t go through!

I still think magic is involved somehow, though.