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On 02/05/2014 11:53, andrel wrote:
>> YABAMBA
>
> not sure what that acronym means but if it means something like GIYF or
> 'why don't you just think before you post' or 'have you heard of the
> concept of newspapers and magazines', I agree.
Yet Another Bogus Assumption Made By Andy
:-)
John
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On 2-5-2014 15:49, Doctor John wrote:
> On 02/05/2014 11:53, andrel wrote:
>>> YABAMBA
>>
>> not sure what that acronym means but if it means something like GIYF or
>> 'why don't you just think before you post' or 'have you heard of the
>> concept of newspapers and magazines', I agree.
>
> Yet Another Bogus Assumption Made By Andy
>
yep, that sort of covers it.
I fear that this could become an often used acronym in this group.
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> Does anybody really use 3D printers much? I mean, I can imagine there
> are products for which this might be really useful, but if you're just
> making (for example) plastic sandwich boxes, do you really need to
> prototype that?
So you'd be confident enough that the sandwich box hinge and latching
mechanism was going to work properly and not snap off, and that it would
feel right, and the MD is not going to complain the box feels too
flimsy, just by looking at CAD data on your screen and perhaps some
simulations that tell you the stiffness is X N/mm at certain points and
you need X N of force to open the latch? Confident enough to sign off
$100000 for the tooling to be made? For the sake of $500 to get a few
prototypes made up it's not worth it. FWIW I've *never* seen tooling get
made exactly right first time, there is *always* something that needs to
be fixed or changed, using prototypes just reduces the risk of any big
(=expensive) errors.
> Also: I was given to believe that 3D printed objects have approximately
> the structural rigidity of jellybaby.
Did you miss the story a while back of the guy who made a functional
*gun* from 3D printed parts? The whole point of professional 3D printed
parts is that they match the performance of the real moulded plastic.
FWIW here we put butanone at 6 bar into 3D printed parts without issue.
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On 02/05/2014 03:34 PM, scott wrote:
>> Does anybody really use 3D printers much? I mean, I can imagine there
>> are products for which this might be really useful, but if you're just
>> making (for example) plastic sandwich boxes, do you really need to
>> prototype that?
>
> So you'd be confident enough that the sandwich box hinge and latching
> mechanism was going to work properly and not snap off, and that it would
> feel right, and the MD is not going to complain the box feels too
> flimsy, just by looking at CAD data on your screen and perhaps some
> simulations that tell you the stiffness is X N/mm at certain points and
> you need X N of force to open the latch?
Given that a 3D prototype will be made of a totally different material
with totally different properties, I'm not sure how having a prototype
lets you check this.
> FWIW I've *never* seen tooling get
> made exactly right first time, there is *always* something that needs to
> be fixed or changed
Really? I find that quite surprising. (Then again, I don't work in this
industry.) I had assumed that by now, making something trivial like a
cube-shaped box would be easy. Of course, if you're making something
complicated like the casing for a camera or something, that seems much
harder to get right...
>> Also: I was given to believe that 3D printed objects have approximately
>> the structural rigidity of jellybaby.
>
> Did you miss the story a while back of the guy who made a functional
> *gun* from 3D printed parts? The whole point of professional 3D printed
> parts is that they match the performance of the real moulded plastic.
> FWIW here we put butanone at 6 bar into 3D printed parts without issue.
That's impressive, given that even "real moulded plastic" isn't strong
enough to make a gun... They're made out of metal for a reason, after all.
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>> Really? I thought *all* transparent materials have an IOR different than
>> air. As in, it's impossible to *avoid* this (e.g., if you wanted to make
>> a kind of "invisible glass", you can't do it.)
>
> You can create a cone structure on the surface of the material (with the
> points upwards so it's pointy to touch). Now so long as the size of the
> cones is smaller than the wavelength of light then you get a continuous
> smooth variation of IOR from the air to the solid. This prevents any
> reflections, so the glass looks invisible.
That sounds absolutely trippy - and really expensive to manufacture. ;-)
> There are other anti-reflection coatings already in use, with varying
> degrees of performance. One of them works by destructive interference
> and is used on glasses, outdoor displays etc, you can tell by the
> characteristic purple tint of the remaining reflection (it blocks green
> reflection mainly).
Yeah, interference is wavelength-specific, so you can only make stuff
non-reflective at one wavelength. I've seen Falstad. ;-)
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Le 02/05/2014 19:26, Orchid Win7 v1 nous fit lire :
>
> That's impressive, given that even "real moulded plastic" isn't strong
> enough to make a gun... They're made out of metal for a reason, after all.
Only if you need to fire more than a few time. The bullet should be
metal, the percussing pin too, and maybe container of powder.
Everything else can be "consumable".
In our modern society, making things that last is so 19th century!
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>> That's impressive, given that even "real moulded plastic" isn't strong
>> enough to make a gun... They're made out of metal for a reason, after all.
>
> Only if you need to fire more than a few time.
I was going to say something about the heat melting the plastic. But
really, the biggest problem is surely going to be that the charge will
smash the plastic to shrapnel, killing whoever fires the gun...
> In our modern society, making things that last is so 19th century!
This makes me sad.
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On 03/05/2014 11:09 AM, Orchid Win7 v1 wrote:
>> In our modern society, making things that last is so 19th century!
>
> This makes me sad.
http://www.bbc.co.uk/news/business-27253103
--
Regards
Stephen
I solemnly promise to kick the next angle, I see.
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On 03/05/2014 11:31 AM, Stephen wrote:
> On 03/05/2014 11:09 AM, Orchid Win7 v1 wrote:
>>> In our modern society, making things that last is so 19th century!
>>
>> This makes me sad.
>
> http://www.bbc.co.uk/news/business-27253103
So many people seem to think that when you buy something, getting the
lowest possible price is the *only* thing that matters. Which is
frustrating, because I'd actually prefer to pay more money for a quality
product. But since that's currently unfashionable, nobody makes those
anymore. (Or if they do, because so few people buy them, they're
*severely* expensive. Manufacturing costs have to be split between a
fewer number of buyers, and all that.) It's not even like buying a more
expensive model even guarantees better quality anymore; anybody can take
an inferior item and just slap a bigger price tag on it...
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> I knew there were at least 6 main plastic types.
No, there are two. Thermosoftening and thermosetting plastics. Each
type has thousands of different molecules.
> But 10,000? Really?
> I can imagine you could have 10,000 different compounds, with different
> additives in them to adjust how springy or brittle they are, etc. But
> 10,000 fundamentally different molecules? Really?
Not necessarily. Take the simplest plastics, such polyethylene, which
is just chains (called polymers) of ethylene molecules (called
monomers). Depending on the length of the chains, you will have
different properties, hence different commercial applications. LDPE and
HDPE behave quite differently.
Also, if you alternate monomers in your chain, you will have different
properties as well. Nylon-4,6 behaves differently than Nylon-6,6 or
Nylon-6,9.
Etc.
> most plastics melt if you pour boiling water on them, never mind
> heating them to *hundreds* of degrees...
>
YABAMBA.
to Google, don't you?
> (Also, if this plastic as such a high melting point, how do you mould it
> in the first place??)
You realize the technology to melt metals - which have higher melting
points than plastics - has existed for millennia.
Also, look into "creep". You don't need to melt it to be able to shape
it. Just like a blacksmith doesn't have to melt iron into a liquid to
make horseshoes or a sword.
Finally, you *must* have come across pots and pans that have plastic
handles. I'm sure these don't melt everytime you boil water.
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