scott wrote:
>> I wonder if they use something like the acid on "frosted" glass...
> 
> There are both mechanical methods and chemical etching methods to make 
> the patterns.  Basically you are just making a pattern on the surface of 
> the metal in the mould.  For one of our plastic products (which is an 
> optical component so is transparent plastic) they make "fine 
> adjustments" to the surface texture by some dude manually "roughening 
> up" the surface in certain positions :-)

Yay for manual roughening up dude! :-D

>> Yeah, well, that's a function of far more than the plastic shell. 
>> Gotta assemble the whole thing for that! ;-)
> 
> Usually you don't do any testing on individual parts, only on the 
> assembled product.

Not even to test that they actually fit together properly? Or is that 
more or less guaranteed before the parts leave the design stage?

(OTOH, I guess that assembling the final item *is* checking that the 
parts fit! :-D )

> Well yeh, if from every single shot you have some waste then it makes 
> sense to work out how to reuse that.  But working out how to reuse 5000 
> samples is a bit pointless if you are planning to make 2 million every 
> month later.

OK, fair enough.

>> And that brings us back to my question about components which are 
>> supposed to "snap together". I guess it depends on how deformable the 
>> plastic is? (And that surely must depend on shape...)
> 
> Yep, or technically "stiffness", which is how much something deforms for 
> a given force (units DISTANCE/FORCE).  You can of course design the 
> shape so that things deform easily for clips, or make springs to hold 
> things in place etc.

IIRC, if you bend plastics they return to their original shape, until 
you bend them past a certain point, at which they deform permanently. 
(They also change colour for no adaquately-explored reason...)

>> Heh, and I bet that's even *more* damed expensive again... not to 
>> mention the quality hardened steel you need for it to mill...
> 
> And then the actual milling bit, which presumably must be harder than 
> the hardened steel :-)

HOW THE HELL DO THEY CUT DIAMONDS?!

>> I wonder... do companies buy all this stuff themselves? Or just 
>> subcontract it out?
> 
> Well you get quite long supply chains sometimes, like take for example 
> car company 1.  They will have supplier 2 that makes some big chunk of 
> the dashboard.  Supplier 2 will have a supplier 3 that provides one part 
> (eg the radio).  Supplier 3 will then use supplier 4 to make the plastic 
> part to go on the front of the radio.  Supplier 4 will own the injection 
> moulding machine, but could well use a supplier 5 to actually 
> manufacturer the tools to go in the injection molding machine.  And of 
> course there will be another supplier 5 that supplies the raw plastic to 
> supplier 4.
> 
> Companies like Nokia and Ford don't actually make much, they just design 
> things and get other people to make them, then assemble bits together 
> :-)  I once saw a Nokia factory, each production line was about 50 
> metres long, they simply screwed some components together, did some 
> electrical and optical testing, clipped the plastic parts on and 
> packaged it into several layers of cardboard boxes.  Very low tech and 
> very simple.

Heh. That explains why if you drive round any small industrial estate, 
you'll find some nobody company that's never been heard of called 
"Lanstead Way Plastics Ltd" or something. They all mould plastics! :-D

>> I also wonder... Today we have machines that make components of 
>> machines that are used to make machines for making machines. Some of 
>> this stuff is made to absurd tolerances - stuff no human could ever 
>> make by hand. So... how the **** did we make it in the first place?!
> 
> Well just because you only have equipment to design and make stuff to 
> tolerance X, it doesn't mean that you can't make a machine that can make 
> stuff to a tolerance lower than X.  eg you could just build a motor and 
> then gear it down a lot so that the movements are very small and 
> accurate, or use optical lens to shrink your design, or use a lever so 
> that a larger tolerance on one end corresponds to a smaller tolerance at 
> the other end.

Yeah, but without precisely machined gears, wouldn't there be too much 
play between the teeth for the position to hold accurately?

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