So does the user sprinkle the powder after each slice, or does the machine somehow do it? How would the machine make an even layer of powder?
I can't make it up from the pictures, but most printers just trow a pile of powder on top of the last layer and flatten this with an arm. But I think this video will show it much more clear: http://www.youtube.com/watch?v=wD9-QEo-qDk (take a look from 1:50).
Why doesn't the powder stick to the print head, or get pushed around unevenly by the print head?
Because the print head never touches the powder. Just like it doesn't touch the paper in your inkjet printer.
Well, you've covered pretty much all questions, but here is a reply from the builder :)
So does the user sprinkle the powder after each slice, or does the machine somehow do it? How would the machine make an even layer of powder?
The storage bin moves up a little and the build bin down, and then a counter-rotating roller (mounted on the XY-carriage) deposites the powder from one to the other bin.
Why doesn't the powder stick to the print head, or get pushed around unevenly by the print head?
Indeed, the printer head is mounted ±4mm above the powder bed and can never touch the powder. See the printer head moving across the powder bed in this video: http://www.youtube.com/watch?v=bzX5x1A1AMg
Why doesn't the powder fall out during printing?
Because the pistons form a seal and don't let the powder fall through.
So does the user sprinkle the powder after each slice, or does the machine somehow do it? How would the machine make an even layer of powder?
Why doesn't the powder stick to the print head, or get pushed around unevenly by the print head?
Why doesn't the powder fall out during printing?