| Comparison steel vs. glass [message #23735] Sat, 12 February 2011 10:22 UTC |
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Wanted to get a better feeling for the materials and ordered these two test prints.
Steel quality is very good, detail reproduction is beyond expectation.
There is significant shrinkage on the glass sample, it also more like a very hard plastic, no real feel of glass.
The glass surface is very bumpy and randomly distorted. Details not very perceivable.
 The digital model has a diameter of 31 mm, the numbers and letters are 0.5 mm thick, the map of Europe +-0.2 mm.
The steel print matches in size, the glass is only 29 mm wide.
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| Re: Comparison steel vs. glass [message #23742 is a reply to message #23738 ] Sat, 12 February 2011 11:27 UTC |
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Yes, it's a good business model. A 1€ coin will only cost about 20$.
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| Re: Comparison steel vs. glass [message #23802 is a reply to message #23742 ] Mon, 14 February 2011 07:26 UTC |
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It's a cool object to include in pictures if you want to make something seem smaller than it is!
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| Re: Comparison steel vs. glass [message #24174 is a reply to message #23802 ] Wed, 23 February 2011 22:29 UTC |
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I like that your coin unites Europe!
It took me until now to realize how Europe is falling apart on real Cent coins!
[Updated on: Wed, 23 February 2011 22:30 UTC]
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| Re: Comparison steel vs. glass [message #24219 is a reply to message #24196 ] Thu, 24 February 2011 20:18 UTC |
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The "shrinkage" is compensated for by printing the green parts 20% larger than the final size. The real shrinkage/ distortion problem is due to the fact that during the sintering process glass, unlike metal, becomes a thick viscous liquid.
Molecular attraction will cause all liquid bodies to pull towards the center of it's own mass. To illustrate; If you heat a tiny chip of glass or metal until it melts, it will always form into a nearly perfect sphere. In zero gravity, like on the Space Shuttle, (go Discovery), a spilled liquid always forms a perfect ball.
So, as a printed glass part begins to fuse and coalesce into a solid mass these forces will come into play. And sometimes in dramatic and unwanted ways. Any angled cross section or cube will shrink asymmetricaly and the result is visually obvious. Faces of a cube will dish in towards the center. A square rod section with become more like a trapezoid. On the other hand, spheres, rounded or curved sections shrink/distort in a more symmetrical manner. Although the same amount of shrinkage is actually occuring, it is just not so noticeable.
Maybe some braniac could create an algorythm to compensate for this phenemona but it's probably simpler to learn and understand how and why materials behave as they do. Then, design good parts within the laws of nature. PUSH THE LIMITS but respect the laws.
-G
"Where the spirit does not work with the hand, there is no art."
Leonardo da Vinci
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| Re: Comparison steel vs. glass [message #24222 is a reply to message #23735 ] Thu, 24 February 2011 20:37 UTC |
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I wish I was smart enough to create that algorithm (not even smart enough to spell algorithm right without spell check). I am currently trying to take advantage of the shrinkage properties of plastic in one of my latest designs (not 3d printed, injection molded).
The Mad Moder
michael@shapeways.com
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| Re: Comparison steel vs. glass [message #24224 is a reply to message #24219 ] Thu, 24 February 2011 21:13 UTC |
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| GlenG wrote on Thu, 24 February 2011 20:18 |
The "shrinkage" is compensated for by printing the green parts 20% larger than the final size. The real shrinkage/ distortion problem is due to the fact that during the sintering process glass, unlike metal, becomes a thick viscous liquid.
Molecular attraction will cause all liquid bodies to pull towards the center of it's own mass. To illustrate; If you heat a tiny chip of glass or metal until it melts, it will always form into a nearly perfect sphere. In zero gravity, like on the Space Shuttle, (go Discovery), a spilled liquid always forms a perfect ball.
So, as a printed glass part begins to fuse and coalesce into a solid mass these forces will come into play. And sometimes in dramatic and unwanted ways. Any angled cross section or cube will shrink asymmetricaly and the result is visually obvious. Faces of a cube will dish in towards the center. A square rod section with become more like a trapezoid. On the other hand, spheres, rounded or curved sections shrink/distort in a more symmetrical manner. Although the same amount of shrinkage is actually occuring, it is just not so noticeable.
Maybe some braniac could create an algorythm to compensate for this phenemona but it's probably simpler to learn and understand how and why materials behave as they do. Then, design good parts within the laws of nature. PUSH THE LIMITS but respect the laws.
-G
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Not a lot to do with molecular gravitation - more like air pressure, a constant all encompasing force makes a liquid try to re-form with the smallest possible surface area, i.e. a sphere... take an ocean and put it into a zero gravity, but pressurized environment and it will become a huge ball of water, let it loose in space (zero gravity, zero pressure) and after some time there will be nothing left.
I know someone who needs his brain exersicing, creating an algorithm to take into account gravity and air pressure might be just the thing to help him get his life back on track... I'll call my Dad in the morning. (seriously, this kind of problem is right up his street!)
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| Re: Comparison steel vs. glass [message #24332 is a reply to message #24224 ] Mon, 28 February 2011 18:41 UTC |
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Right,
Gravity is only a problem if a glass print is not properly supported during the firing cycle. Improperly supported parts will sag during firing due to gravity. This is only a problem for the technicians though.
The "molecular attraction" I referred to, as a cause of distortion, has nothing to do with gravity. More properly, I should have said that it is surface tension that causes angular forms and sections to distort and contract unevenly. And yes ambient (air) pressure contributes to this as well. I believe the only way to compensate for this effect would be to distort the computer model. For instance; if you want to print a perfect cube you would need to model it with bulged faces that would contract just enough during firing so that the final part would turn out square and true. Some pretty complicated math would be involved.
-G
"Where the spirit does not work with the hand, there is no art."
Leonardo da Vinci
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| Re: Comparison steel vs. glass [message #24334 is a reply to message #23735 ] Mon, 28 February 2011 19:30 UTC |
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| trompevenlo wrote on Sat, 12 February 2011 10:22 |
The digital model has a diameter of 31 mm, the numbers and letters are 0.5 mm thick, the map of Europe +-0.2 mm.
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Good info, but what is the overall thickness of the metal one and when was it printed? The reason I ask is the current problems with Shapeways metal printing where some models at 1mm thickness are printed while others any less than 3mm won't be...
Glenn
Glenn ------ My Website Third Dimension Jewellery
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| Re: Comparison steel vs. glass [message #24343 is a reply to message #24334 ] Mon, 28 February 2011 21:55 UTC |
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| lensman wrote on Mon, 28 February 2011 19:30 |
... the current problems with Shapeways metal printing where some models at 1mm thickness are printed while others any less than 3mm won't be...
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These coins were not done as a thickness test and do not count for that purpose.
As far as I can tell, there is no strict 3mm rule. It very much depends on the operator who inspects your model. You may get a generous operator one day, a more strict one may reject the same thing next day. (not limited to metal printing, BTW)
Keep in mind that neither Shapeways nor their contractors have an incentive to allow extra-thin models. It has very little effect on their efficiency, and the price structure is more than clear: The thicker, the better ...
Yes, it's frustrating at times, but the bottom line is: Don't take a rejection as the definitive answer, don't commit yourself to tight deadlines, keep trying and trying and ...
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| Re: Comparison steel vs. glass [message #24344 is a reply to message #24343 ] Mon, 28 February 2011 23:02 UTC |
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I recently got rejected on some very small thin 3D letter "A" items, but I was surprised when they turned up in the mail some time later.....
[Updated on: Mon, 28 February 2011 23:32 UTC]
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| Re: Comparison steel vs. glass [message #24348 is a reply to message #23735 ] Tue, 01 March 2011 00:58 UTC |
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Exactly. Consistency is needed when trying to run a business (or at least give the appearance of being professional when offering items to the public).
Glenn
Glenn ------ My Website Third Dimension Jewellery
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| Re: Comparison steel vs. glass [message #24364 is a reply to message #23735 ] Tue, 01 March 2011 18:01 UTC |
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Glenn,
I can tell you consistency is in the works. Probably right around top priority (somewhere up there with silver)
The Mad Moder
michael@shapeways.com
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I wonder if the glass shrinkage can be compensated for?
