> I'm presuming a mould with a fake-leather texture to it has gotta be 
> pretty expensive to make...

You mean like the one you have on the dashboard in your car?  The texture on 
the plastics on your car dashboard is both to give it a "quality" feel but 
also to avoid specular reflections from sunlight etc.

> Yeah, I guess if you want to check the bits fit together, a 3D model is 
> fine, but if you want to see how strong it is, you need to use the real 
> material that the final product will use.

Or if you want to check it will last OK continually in temperatures of -30 
degrees or +40 degrees (other countries outside of England have much more 
extreme temperatures, and things must still work ok).  Or if you want to 
check it still works after you drop it on the floor etc, that sort of thing.

> Reading Wikipedia, it appears that "most" plastic items are thermoplastics 
> rather than thermosetting. Is that true? Does that mean there's a 
> possibility of reusing your prototypes once you're done with them?

I don't think so, the cost of reprocessing the parts into something the 
plastics maker could use would be too high.

>> +/- 0.1 mm is pretty easy to achieve in a single shot plastic injection, 
>> that sounds about right for a CD hinge to work.
>
> That sounds really damned tiny! o_O

But think about it, if the hinge on one side was just 1mm off, it's not 
going to work at all.

>> A quick google reveals that chapter 6 of the USB spec specifies that :-) 
>> The outline dimensions of the plug are +/-0.1mm, but some of the pin 
>> spacings and inner dimensions are down to +/- 0.05
>
> Wow. OK, that's pretty small...

But again, think about what your USB plug would feel like if it was just 
0.5mm too wide, it wouldn't feel like it should and the plug would come off 
too easily.  That's why a smaller tolerance is necessary for some parts.

> Suddenly I'm wondering what the tolerances are for those *tiny* little 
> screws they have on things like spectacles. ;-) Man, the thread on those 
> is tiny!

Yeh, imagine the tolerance on the thread pitch of those :-)  Something 
insane like 0.02 +/- 0.005 mm !

> You might even know this one... What is the total travel on the buttons of 
> a mobile phone? I mean, you can "feel" them click, but visibly they hardly 
> seem to move at all! (But then, I hypothesize that the inside of a mobile 
> phone is a very cramped place.)

Don't know, but usually there are just tiny rubber "poppers" underneath, a 
bit like those toys you used to have as a kid that were like a thick 
hemisphere shell of rubber, you turned them inside out and set them down, 
then after a few seconds they jumped up in the air.  The click you feel on 
the keys is when the rubber "snaps" in and out of shape.

> Damn. So after some guy designs what the final thing is even meant to look 
> like, some other dude has to figure out what seperate bits to make and how 
> to slot them together, and then yet another guy has to figure out how the 
> **** to build something to make stuff that shape! o_O

Exactly - and you begin to realise how expensive, how many people, and how 
much time it takes to design something apparently simple like a mobile 
phone.  Then imagine designing something like a car, or a plane! It's just 
not possible to imagine how much work goes into such a product.

> Heh. Damn... I wonder how they cut the mould to exactly the right shape?

You can get milling machines that are controlled by very accurate stepper 
motors, a computer sends a list of commands to the machine and it moves the 
cutting bit around.

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