> 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.

Post a reply to this message

scott wrote:
>> 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?

Yeah, like that.

Or in fact, just now I was looking at a cheap knife. The blade is a lump 
of metal that's just about sharp enough to cut bread, and the handle is 
a blob of black plastic that looks like it's injection-moulded. (It has 
a fetling line on it.) But then I noticed, the plastic has a rough 
texture to it. (To enhance grip?) How do they do that?

I wonder if they use something like the acid on "frosted" glass...

>> Yeah, I guess 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 still works after you drop it on the floor etc, that 
> sort of thing.

Yeah, well, that's a function of far more than the plastic shell. Gotta 
assemble the whole thing for that! ;-)

>> 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.

Apparently by dad spent some time working in a plast where they do 
"vacuum forming", and each time you do that, you have to cut a bunch of 
wasted plastic off the edges. He says they sent it back to the suppliers 
and they got a discount. (But then, how hard can reprocessing a flat 
sheet of plastic be?)

>> 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 !

Hee... must be expensive! ;-)

>> You might even know this one... What is the total travel on the 
>> buttons of a mobile phone?
> 
> 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.

Right.

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...)

>> 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.

I wouldn't have called a mobile phone "simple", but yeah. I was thinking 
more something like a pen. (They usually have that click-action that 
allows you to retract the tip. And a lid that needs to fit properly. And 
the tip is usually metal, not plastic. And you need to fill it with ink 
somehow...)

It kinda makes you wonder how anything ever gets made in the first place!

>> 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.

Heh, and I bet that's even *more* damed expensive again... not to 
mention the quality hardened steel you need for it to mill...

I wonder... do companies buy all this stuff themselves? Or just 
subcontract it out?

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?!

Dude, HOW DO YOU BOOTSTRAP CIVILISATION?! O_O

Post a reply to this message

Now, see, this is what I love about off-topic... There's so many people 
here who know interesting stuff! :-D

Post a reply to this message

> 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 :-)

> 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.

> Apparently by dad spent some time working in a plast where they do "vacuum 
> forming", and each time you do that, you have to cut a bunch of wasted 
> plastic off the edges. He says they sent it back to the suppliers and they 
> got a discount. (But then, how hard can reprocessing a flat sheet of 
> plastic be?)

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.

> 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.

> It kinda makes you wonder how anything ever gets made in the first place!

Yeh I often wonder that too...

> 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 :-)

> 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.

> 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.

Post a reply to this message

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?

Post a reply to this message

Invisible wrote:

>> 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...

Pff.. That's nothing :) The jigging system I worked on cost about US$1M 
for a decently sized system. ~US$100K per 4 axis table. Our saws ran 
about US$100K-250K

I'm guessing Injection molding machines don't have computer controls. 
I'd imagine the engineering costs are pretty high, though ... getting 
all of the pathways right so the part fills the mold properly, and cures 
properly.

> 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.)
> 

My el-cheapo Casio has a metal chassis. Ask me how I know ... I had to 
pull it apart to fix the MIDI out port ... stupid thing came un-soldiered.


-- 
~Mike

Post a reply to this message

>>> 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...
> 
> Pff.. That's nothing :) The jigging system I worked on cost about US$1M 
> for a decently sized system. ~US$100K per 4 axis table. Our saws ran 
> about US$100K-250K

Jig system?

What are you trying to cut? Kryptonite??

> I'm guessing Injection molding machines don't have computer controls. 
> I'd imagine the engineering costs are pretty high, though ... getting 
> all of the pathways right so the part fills the mold properly, and cures 
> properly.

More to the point, apparently IM machines are rated on the amount of 
pressure they can clamp the mould down with - measured in tonnes. (!) 
Apparently the cheap ones manage 3-4 tonnes, and the best reach 6,000 
tonnes or more. O_O

> My el-cheapo Casio has a metal chassis. Ask me how I know ... I had to 
> pull it apart to fix the MIDI out port ... stupid thing came un-soldiered.

You as well?

(Actually, you should be glad it even *has* a MIDI port in the first 
place! Most cheap keyboards don't.)

We had to take my old ghettoblaster apart after the line in became 
loose. After we soldered it back down and reassembled it, we found one 
small metal part left over. We still don't know what that was!

Ah, that was a *quality* piece of equipment though. The box boasts 200W 
of power, but the actual speakers inside had figures of fractional Watts 
crudely printed on them. (2x speakers at 0.5W, 2x woofers at 0.25W.) And 
the manual described the line-in sockets as having "> 14% THD". :-D

Post a reply to this message

Mmm, tasty...

http://en.wikipedia.org/wiki/Injection_molding
http://en.wikipedia.org/wiki/Electrical_discharge_machining
http://en.wikipedia.org/wiki/Electro_chemical_machining

Post a reply to this message

Invisible wrote:

> 
> Jig system?
> 
> What are you trying to cut? Kryptonite??
> 

Jigging -- A means of holding something together while you work on it. 
Tack on another 10K for the rolling press... btw. (You have to press the 
plates into the truss.)

The saws cut ordinary wood, but they're robotic. Lots of engineering and 
programming time goes into them.


> 
> More to the point, apparently IM machines are rated on the amount of 
> pressure they can clamp the mould down with - measured in tonnes. (!) 
> Apparently the cheap ones manage 3-4 tonnes, and the best reach 6,000 
> tonnes or more. O_O
> 

If you can find it in your country, check out the show "How Its Made" 
Here it appears on the Discovery Science network. They detail many 
industrial processes. It blows my mind how these huge presses seem to 
stamp out such things as screwdrivers with nearly no effort.

The U.S. mint apparently uses 84 tons of pressure to press a coin. All 
applied in an instant! Hundreds of times a minute.


> 
> You as well?
> 
> (Actually, you should be glad it even *has* a MIDI port in the first 
> place! Most cheap keyboards don't.)
> 

Well, I had aspirations of creating music on the computer a long time 
ago, and decided a MIDI keyboard was the appropriate input device. That 
didn't work out... :)



-- 
~Mike

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"Invisible" <voi### [at] devnull> wrote in message 
news:494655da$1@news.povray.org...

> It kinda makes you wonder how anything ever gets made in the first place!

    Yes, you need a lathe to make a lathe.

     ~Steve~

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