On 1-5-2014 19:41, Orchid Win7 v1 wrote:
> Does anybody really use 3D printers much?

My dentist.

>
> Also: I was given to believe that 3D printed objects have approximately
> the structural rigidity of jellybaby. It's strong enough to see if
> various printed parts will fit together right, but if you stare at it
> too hard you're gonna break it. But hey, it's only a *prototype*, right?
> It's not like the finished item will be made of the same gel...

My dentist makes bridges and crowns with a 3D printer, and the products 
are no jellybabies, thank God. :-)

Thomas

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> I was under the impression that 3M's main business is *manufacturing*
> plastics, not designing new ones.

It's both - if they didn't do the latter they would be no different to 
the other 10 million plastic manufacturing plants. If you've ever dealt 
with 3M (as a supplier for volume manufacturing) you would know they are 
not the cheapest, but they often have materials and technologies that 
nobody else has. This is their business model, it is not making 
bog-standard plastics cheaper than everyone else (they would never win 
this).

> (Actually, I was under the impression
> that 3M manufactures finished products that have plastic _in_ them, but
> I guess they probably sell raw plastic to other people...)

I don't think they do much of that, maybe for some specialised areas but 
I've never heard or seen anyone sourcing raw plastic from 3M.

> 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. I've seen prototypes of this 
and it really does look invisible (you can stick a patch of it on glass 
and it looks like someone cut a hole in the glass). The obvious problem 
with this is the tips of the cones wear off quite easily which starts to 
reduce the effect. Again, it's all about developing new materials and 
processes to achieve this kind of product.

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).

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On 1-5-2014 22:38, Doctor John wrote:
> On 01/05/14 18:41, Orchid Win7 v1 wrote:
>> Granted I don't work in the manufacturing industry. But I would have
>> expected that the market for rapid prototyping is utterly *tiny*
>> compared to the market for actual finished goods.
>>
>> 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?
>>
>> Also: I was given to believe that 3D printed objects have approximately
>> the structural rigidity of jellybaby. It's strong enough to see if
>> various printed parts will fit together right, but if you stare at it
>> too hard you're gonna break it. But hey, it's only a *prototype*, right?
>> It's not like the finished item will be made of the same gel...
>
> 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.

Anyway, we use our 3D printers a lot in the hospital, e.g. to plan 
operations. Also, have a look at shapeways.com . Do you want plastic 
(several varieties) , sandstone, metals, or ceramic?


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> That's a pretty sharp cuttoff. OTOH, from this scale you can't tell
> whether the filter still passes, say, 1% of the UV. 1% UV is presumably
> still easily enough to utterly destroy whatever is underneith. (E.g., a
> plastic coated in this stuff will get ruined in a few months rather than
> a few days.)

I don't think many dyes fade within a few days of sunlight exposure. A 
few months maybe, but then a 1% UV filter will allow them to last a few 
decades, which is actually useful for something like a car or a photo.

> So... essentially you're saying the only real change is that plastic is
> cheaper now?

Not really, what I'm saying is that the development of plastics and the 
processes that use them have allowed *products* to become cheaper. But 
that's pretty much the entire purpose of engineering, to make a product 
that meets all the requirements for as low a cost as possible. If you 
can come up with a new material (or a variant on an existing one) that 
allows an existing product to be made cheaper you will be collecting the 
$$$.

> I knew there were at least 6 main plastic types.

Correct, there are at least 6 :-) Here's a list of the common categories:

http://www.efunda.com/materials/polymers/history/history.cfm?list_order=name

There are about 40 there. If you click on each one it will give you a 
list of common grades, about 20 for each of the ones I clicked on. 
That's already 800 different grades without even considering various 
combinations of other additives to aid manufacturing or specific 
properties needed. My point is that if you plot all of these on a 
timeline you'll see that most have been developed fairly recently, it's 
not like there's no development in plastics.

> (Also, if this plastic as such a high melting point, how do you mould it
> in the first place??)

Make your manufacturing machinery from something with a higher melting 
point, say steel? How do they make the steel in the first place? :-)

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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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