What are flexible curves made of?

eram

eram

Sciengineer
Valued Senior Member
This may sound like a trivial question but i can't find the answer online. I bought this flexible curve some time ago. It's a flexible ruler that allows one to draw curve functions.

It consists of a rubber casing and a strip of malleable metal inside. What is that metal? Is it lead? I hope not.
 
eram said:
This may sound like a trivial question but i can't find the answer online. I bought this flexible curve some time ago. It's a flexible ruler that allows one to draw curve functions.

It consists of a rubber casing and a strip of malleable metal inside. What is that metal? Is it lead? I hope not.
Click to expand...

The ability of metals to retain the shape they are formed in is called "malleability" . Copper is used in several flexible rulers.
http://www.sbsmodel.com/ruler

OTOH , the ability of flexible rulers to return to their original (flat) shape after being distorted is called "elasticity". These usually have a thin steel plate inside a plastic casing.

http://www.americanmachinetools.com/properties_of_metal.htm
 
ok i tried to melt the metal inside the metal ruler, i assume that its melting point is below 1,950C since my stove is fueled by natural gas. the metal is grey and silvery when i left it out for a few days, so rest assured mine is probably not lead.
 
Write4U said:
The ability of metals to retain the shape they are formed in is called "malleability" . Copper is used in several flexible rulers.
http://www.sbsmodel.com/ruler

OTOH , the ability of flexible rulers to return to their original (flat) shape after being distorted is called "elasticity". These usually have a thin steel plate inside a plastic casing.

http://www.americanmachinetools.com/properties_of_metal.htm
Click to expand...
Elasticity has little to do with it. Flexible curves are plastic rather than elastic. Elastic means spontaneously returning to the original dimensions when deforming stress is removed. Like a spring, for example. That is exactly what a flexible curve does not do. It retains the shape it is given. That is plastic behaviour.

I don't know the construction but mine bends only in 2 dimensions, strongly resisting bending "up" or "down", relative to the flat on it designed to rest on the paper. I had always assumed there must be some mechanism a bit like a bicycle chain inside, it to achieve the flexibility in one plane only, plus something like lead to give the plastic deformation. But I'd be interested to know.

By the way, it seems early versions of this device were apparently known as "Lesbian rules". :Dhttps://en.wikipedia.org/wiki/Lesbian_rule
 
Last edited:
exchemist said:
Elasticity has little to do with it. Flexible curves are plastic rather than elastic. Elastic means spontaneously returning to the original dimensions when deforming stress is removed. Like a spring, for example. That is exactly what a flexible curve does not do. It retains the shape it is given. That is plastic behaviour.
Click to expand...
Is it not desirable to have a ruler be as straight and flat as possible? Elasticity ensures a return to its original flat/straight shape.

http://www.americanmachinetools.com/properties_of_metal.htm
 
Write4U said:
Is it not desirable to have a ruler be as straight and flat as possible? Elasticity ensures a return to its original flat/straight shape.

http://www.americanmachinetools.com/properties_of_metal.htm
Click to expand...
Not a flexible curve, though. The purpose of these is to enable a smooth curve to be drawn through a set of points to form a line graph, or to follow a curved shape so that it can be reproduced in a drawing.

For that, you want something that can be moulded by hand to fit a curve and then will retain that shape, to allow it to be traced with a writing instrument. The last thing you want is for it to spring back to its original, straight shape.
 
eram said:
It consists of a rubber casing and a strip of malleable metal inside. What is that metal? Is it lead? I hope not.
Click to expand...
Lead is not dangerous unless you eat it.

Don't eat it. You'll be fine.

The big health scare around lead is about ingesting it - and doing so in toxic quantities. When unconstrained, it can inadvertently get into your system (say, by unsupervised kids eating a lot of lead-impregnated paint chips).

But since the curve is encased in plastic, you're not in direct contact with it. And even if you were, you're still not in any danger, unless you take it to bed and cuddle with it.

(Note: the dose is the toxicity. Every substance has a toxic level - even water. You normally don't concern yourself with whether you've ingested a toxic dose of water. Lead too, has a toxic dose. It's less than water. Lead is not some magical lethal substance.)
 
It seems to me that the main purpose of the plastic coatong would be to protect the user from the toxic lead - and to protect the soft lead from damage.
 
You must log in or register to reply here.
Back
Top