Progess on the SLS front!
Via @Nils_Hitze
Originally shared by Andreas Bastian
https://www.youtube.com/watch?v=-qbLxL3KBKE&feature=autoshare
It is interesting seeing them use a honeycomb fill on a powder-bed print, though - if they use solid fill on the ends, they have solid metal containing powder that is trapped within, so they’ve saved time in printing, perhaps, but not weight. Then again, maybe they aren’t solid filling on the ends.
@Howard_C_Shaw_III I had the same problem when printing with my DLP resin printer - if the model was a closed but hollow then resin would be trapped. I never progressed beyond test prints, but I suspect some draining holes would have sufficed, or designing parts with open sides, etc.
I believe the professional printing services ensure there are entry and exit holes and use compressed air to eject the spare material.
Even if you don’t drain out the loose powder, cross bracing across the interior is still important because loose powder can move and settle, leaving the sidewalls with little support.
What’s the material in this video? Powdered nylon? Sugar?
It’s apparently wax - @Andreas_Bastian mentions it in the description of his other videos: https://www.youtube.com/channel/UCM8-DF_04jx3tAk_ob5OxYA?feature=watch
When a new layer get pushed over the top of the part it looks like it doesn’t need to be very smooth to still work.
Smoothness never hurts. 
The “tracks” in the loose powder will show as irregularities in the surface. If the tracks are repeated in several layers (like something stuck to the spreader), it can lead to structural failure.