Printing in "Sandstone" - What determines quality of final print?

[RakS]

Hi all,

A question for those who know about printing in gypsum composite/sandstone.
I'm planning to use photogrammetry to create a data-model, which I then intend to print.
Of course, the quality of the photos I take (lighting, focus, megapixels, etc.) is important, and I'm sure that the quality of the data-model I end up with will also have a huge impact.

How much does quality vary from printer to printer, if they are the same model?
i.e. If I print on a 3D systems Projet 660 in "location 1," with the same data set, would I get an identical print in "location 2"

Also, can someone tell me the difference between a prorgam like Photoscan, and one like ZBrush? When printing regular 3D figurines of humans in Sandstone, printed up to 25cm tall, is ZBrush necessary?

Thanks,

Rak.

[awerby]

Photogrammetry has problems of its own which are unrelated to the issues of printing in "sandstone". You're unlikely to get as consistent a model as if you'd constructed it in a program like ZBrush. Your model will probably benefit by a clean-up in a program like that, particularly to even out the color discrepancies introduced by the various different photos, but if your model is "water-tight" (no tiny holes) then it's not absolutely necessary. But if you're doing full-size humans, I think you'll have better luck if you use a 3D scanner like the Sense rather than trying to make solid objects from photographs.

While different machines of the same brand will work somewhat differently, you probably won't notice much difference in the prints from one service bureau to the next. The most variable process will be the infiltration, which is used to give strength to the otherwise very fragile material. The most popular infiltrant is cyanoacrylate (superglue) but other things are sometimes used as well.

Andrew Werby
www.computersculpture.com

[RakS]

Photogrammetry has problems of its own which are unrelated to the issues of printing in "sandstone". You're unlikely to get as consistent a model as if you'd constructed it in a program like ZBrush. Your model will probably benefit by a clean-up in a program like that, particularly to even out the color discrepancies introduced by the various different photos, but if your model is "water-tight" (no tiny holes) then it's not absolutely necessary. But if you're doing full-size humans, I think you'll have better luck if you use a 3D scanner like the Sense rather than trying to make solid objects from photographs.

While different machines of the same brand will work somewhat differently, you probably won't notice much difference in the prints from one service bureau to the next. The most variable process will be the infiltration, which is used to give strength to the otherwise very fragile material. The most popular infiltrant is cyanoacrylate (superglue) but other things are sometimes used as well.

Andrew Werby
www.computersculpture.com

Thanks for your comprehensive answer, Andrew.
In this case, I guess it's possible to outsource the design/cleanup to anyone (globally), and simply print locally?

In terms of infiltration, could you enlighten me as to the alternatives to cyanoacrylate? What are the positives/negatives to these various different infiltrations? Are they ever used to fill the interior of the structure completely, as I believe most are printed hollow?

Thanks again for your time.

[awerby]

Sure, I suppose you could get the design from anywhere in the world and print it where it's most convenient or cheapest.

Infiltration can be done with a range of substances. Originally, when the Z-corp machines printed in a starch-based powder, a clear wax was used; the piece was dipped in a vat of molten wax and wiped clean before cooling. This would probably work with the gypsum-based powders as well, but it doesn't impart a whole lot of strength. There's also an epoxy-based infiltrant, which is mixed before application from two parts, and which sets after being absorbed into the part. But like all epoxies, it tends to go yellowish with time. Personally, I hate working with cyanoacrylates, and don't like epoxies much better, so I use a single-part quick-dry polyurethane varnish as an infiltrant. It takes longer to apply, since several coats are required, and it's not ultimately quite as strong, but the color is neutral and it hasn't caused any health issues for me so far.

Andrew Werby
www.computersculpture.com