Comparison steel vs. glass

Discussion in 'My Shapeways Order Arrived' started by kontor_apart, Feb 12, 2011.

  1. kontor_apart
    kontor_apart New Member
    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.

    DSC00079 (Large).JPG 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.
     
  2. Kaetemi
    Kaetemi New Member
    You're printing money? xD
    Interesting comparison picture, though.
    Useful to know about the glass shrinkage. :)
     
  3. kontor_apart
    kontor_apart New Member
    Yes, it's a good business model. A 1€ coin will only cost about 20$.
     
  4. B1lancer
    B1lancer New Member
    It's a cool object to include in pictures if you want to make something seem smaller than it is!
     
  5. Schmiegel
    Schmiegel New Member
    I like that your coin unites Europe!

    It took me until now to realize how Europe is falling apart on real Cent coins!
     
    Last edited: Feb 23, 2011
  6. Magic
    Magic Well-Known Member
    /* slightly-off topic
    Actually Europe falling apart is the old design. It has been replaced by a new one where Europe is only one for two reasons:
    - the continuous elargment of Europe (or more exactly of Euroland) that made the design obsolete
    - a problem of copyright, if I remeber well
    http://en.wikipedia.org/wiki/Euro_coins
    slightly off-topic */
    :)
     
  7. Youknowwho4eva
    Youknowwho4eva Shapeways Employee Community Team
    If they changed the name of Europe to Euroland, I would be more likely to visit. As long as y'all build some cool water slides and roller coasters. :p I wonder if the glass shrinkage can be compensated for?
     
  8. GlenG
    GlenG New Member
    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
     
  9. Youknowwho4eva
    Youknowwho4eva Shapeways Employee Community Team
    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).
     
  10. stop4stuff
    stop4stuff Well-Known Member
    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!)

     
  11. GlenG
    GlenG New Member
    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
     
  12. lensman
    lensman Well-Known Member
    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
     
  13. kontor_apart
    kontor_apart New Member
    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 ...

     
  14. samdekok
    samdekok New Member
    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.....
     
    Last edited: Feb 28, 2011
  15. lensman
    lensman Well-Known Member
    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
     
  16. Youknowwho4eva
    Youknowwho4eva Shapeways Employee Community Team
    Glenn,

    I can tell you consistency is in the works. Probably right around top priority (somewhere up there with silver)
     
  17. gkaste
    gkaste New Member
  18. Youknowwho4eva
    Youknowwho4eva Shapeways Employee Community Team
  19. gkaste
    gkaste New Member
    Thanks