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Rapid Prototyping Question polygons and nurbs??? calling for experts

ZBrush Usage Questions
#1

O.K This is a question regarding the polygon resolution required for rapid prototyping. I don’t understand how the polygon density will be translated to real model in rapid prototyping.

For easy understanding, if I want to make a 2 x 2 x 2 meter ball, (I do want to make a big thing with lots of details), how can I be sure how many polygons will be enough to guarantee a very smooth surface?

I understand that zbrush works with quads or triangles poly mesh surface, which will result in rough surface if enlarged to a big scale, but in Nurbs surface this will not be an issue.
Should I try to convert mesh to Nurbs? Which software is best in doing this? Geomagic studio?
If I convert a mesh object with the kind of detail common to Zbrush (for instance lots of wrinkles) to Nurbs, will the details be kept?

else where I read, that for rapid prototyping the stl file whould not be bigger than 250mb. Is this true?

#2

  1. Simplest way is to judge it proportionally. In other words, imagine the scale at which you’d want the piece printed & make sure your resolution matches. Typically the machines are unable to replicate the finest details ZB is capable of unless you’re making a huge piece, so if the model look good on the screen you should be fine in the print.

  2. Nurbs will not help anything because the file will need to be converted to an STL (tris) to print so what matters more is the resolution of your STL file. This is an adjustable option in some softwares STL exporters. In ZB it’s closer to the resolution of your model unless you’re decimating.

  3. I used to own 2 Objet printers & their max file size was 250MB. Anything larger would crash the software. This may have changed over the last year or so but I’m not sure. The decimation plugin is great for managing file sizes & is very good at not losing details until you get to more extreme settings.

#3

many many thanks shhark, that answers lots of myquestions.

When you say when things look good on my screen it should be alright in prototyping scale, do you mean if I want to make a 2x2x2meter ball, I should enlarge it to that scale on my screen and see a fine surface?
I wonder how things work in automotive manufacturing. For instance, if I designed a car’s exterior, I want to prototyping it through CNC, that must be a huge stl file, since the car is so big in real size! how do those in automotive industry make sure they get the right number of polygons?

Material
if I want to prototyping in aluminum, is my only choice to be CNC? How about SLA?

Surface finishing
Regarding surface finishing, I saw some pictures on the web, for example Hiroshi’s link (http://www.zbrushcentral.com/showthread.php?t=47708&highlight=Print+toys), the surface of his toy looks very soomth. He seems to be using Dimension BST, is that SLA machine? But in other cases, I notice some models come with lots of unified carving lines on the surface, is that because of SLS?

#4

First thing is I’m unaware (doesn’t mean it doesn’t exist) of any 3D printer large enough to print a 2x2x2 meter ball in one piece. Are you planning on splitting this into smaller pieces? As far as resolution, yes you should try to emulate what the actual scale would be on your screen (you’ll obviously only be able to view a small section) to verify appropriate resolution for you model. If you were sculpting a car exterior & wanted to build it via 3D printers you would also have to make sure the resolution matches the scale just like with anything else.

If you’re looking to have it CNC’d then that could change alot of things but not so much if you’re making the model in ZB. Even though many CNC CAM packages can now read STL files they typically have used more traditional CAD formats (STEP, XT, IGES, etc) which your Nurbs program (ie Rhino) would be perfect for. You will not be able to develop the high level of organic sculptural detail like you can in ZB though. Also, with CNC you are limited in detail by cutter size. While it is possible to get cutters just a few thousandths of an inch in diameter or even with cone tip points it becomes prohibitively time consuming to make all the passes over a large surface with that fine of a cutter.

There are many process & technologies on the market that all build differently as far as resolution, material, speed, etc. Finding the best one for you is typically a balance between the scale of your model (larger requires less printer resolution), budget, & material requirements. Read through my tutorial on 3D printing tutorial to learn more about the different processes & their individual pros & cons.

Depending on what your model is you may want to consider having it machined in aluminum or having it printed in a burnable material that can be used as a pattern for casting (see my thread on my cast bronze tangles ). There are also some process that print in metal. Do a search for 3D metal printing to get you started learning about them.

#5

I found this images, they are prototyped parts.
Are the lines/textured surface on them inevitable to rapid prototyping, or just because it may be the result of SLS?

By the way, your bronze cast is so amazing. It must be a difficult casting process!

[<img src=“http://www.zbrushcentral.com/pixo/atn.gif”>
[url=“http://www.zbrushcentral.com/zbc/faq.php?faq=vb_read_and_post#faq_zbc_display_images”]<img src=“http://www.zbrushcentral.com/pixo/atn.gif”>](http://www.zbrushcentral.com/zbc/faq.php?faq=vb_read_and_post#faq_zbc_display_images)

Attachments

aerospace-4.jpg

#6

I found this images, they are prototyped parts.
Are the lines/textured surface on them inevitable to rapid prototyping, or just because it may be the result of SLS?

By the way, your bronze cast is so amazing. It must be a difficult casting process!

[<img src=“http://www.zbrushcentral.com/pixo/atn.gif”>](http://www.zbrushcentral.com/zbc/faq.php?faq=vb_read_and_post#faq_zbc_display_images)

#7

The process used to build those is most likely DMLS (Direct Metal Laser Sintering). SLS stands for Selective Laser Sintering & is basically the same process but with different materials (nylon & glass instead of metal). The build lines are inherent to the process & inevitable. You could sand & polish the part but you would of course lose detail. Another option would be to get an Objet or SLA printed then have it electroplated. It’s not solid metal but looks like it.