scott wrote:
>> OK, so now I'm wondering. How much does it cost to buy 1 Kg of plastic?
> 
> The cost of the plastic itself is almost zero compared to the other 
> costs involved (like the tooling cost, cost of running the machine, 
> paying workers to keep an eye on the machine, shipping the product etc).

So the plastic itself is pretty cheap?

This leaves me wondering why so many pastical items seem to be 
specifically shaped to be hollow so they use less plastic. I mean, if 
plastic is so cheap, why bother with more elaborate designs to try to 
conserve it?

Is this stuff priced in pounds of Kg or per tonne?

> A typical hard-tool for a simple plastic part (eg the front cover of 
> your CD drive or half of a simple keyboard shell) will cost of the order 
> of 10-40k pounds.

o_O

Ouch...

Now, is that just the mould, or the entire machine? (I would have 
expected the mould itself to be a replacable component, while the rest 
of the machine isn't...)

> That tool will last for perhaps 200k uses until the 
> metal is worn away enough that any further parts produced are considered 
> not good enough.

Really? I hadn't realised they wear so fast.

> So a supplier would give you a price of like 10p per 
> part if you were ordering large enough quantities.

By "large enough" we're presumably talking about tens of millions of units?

> The exact cost of the tooling usually depends on how many details there 
> are in the design, someone has to design and make the tool, so the more 
> details there are the more expensive.

Yeah, figures. So a plastic cup is going to be pretty cheap, but a 
complicated jig for holding a structure together isn't.

>> Also... I have a keyboard sat next to me. It seems very heavy. Is the 
>> *entire* thing plastic? Or is there a metal chasis inside?
> 
> Not sure, maybe in the old days if you had a big heavy keyboard it would 
> have one, but I guess with recent cheaper designs they realised that 
> actually there is no reason to put a metal chassis in there (it's not 
> like a keyboard needs to be that strong in normal use!).

Perhaps I should clarify: I'm talking about a "keyboard" of the musical 
kind. Somebody might attempt to put it on a stand that only supports the 
ends of the unit, and it's over a meter wide. (Even so, all it contains 
inside is a circuit board. No batteries or power supply or anything 
heavy, just the key action.)

> Tools to make metal parts are usually more expensive, because they are 
> more complex.  They often need to bend and cut the sheet metal in 
> several steps to quite accurate tolerances.

Have you ever noticed that cheap PC cases always have jagid edges on 

beautifully smooth? (And the steel seems about 4x thicker, BTW.)

I have no idea what steel costs per Kg, but presumably a lot more than 
plastic! Also, presumably thick steel takes more effort to bend and cut...

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