3d Design/Printing Q&A

In response to some questions from Andrew:

• Do you make your tanks solid or hollow?
  — Hollow. Shapeways charges by material volume as well as machine space, so the less material I can use, the cheaper. Especially in their high-rez FUD/FED resin.
• If hollow, do you put in a honeycomb to add strength?
  — No, in these scales the walls are strong enough at the thickness I use, and honeycombing and using thinner walls wouldn't save me any material volume in the end.
• And how do you decide to how thick to make the walls?
  — The minimum unsupported wall printing thickness is 0.6 – 0.7mm; I usually make the shell walls at least twice that.
• When making a tube (like an exhaust pipe or gun barrel) do you go for hollow or not?
  — Always solid. It's less problematical. I'll maybe add a dimple in the end of large-bore guns. It's really only worth while for models printed in FUD/FED though.
• I'm sure there are design decisions as to whether you build from the bottom-up, or lay it down upside-down, or even end on, or on its side. I guess you find this out through trial and error?
  — The application I primarily use, Blender, defaults to Z-up. Shapeways uses Y-up for display renders. However, when exporting to .OBJ from Blender, you can set the up/down and forward/back axes.
  There seems to be little point in trying to design for a specific printing orientation though. Shapeways crams as many jobs into the machines as possible, which means rotating things to make them fit in any available gaps. They'll even print one job inside another, if there's sufficient clearance.
• Does Shapeways take the OBJ "as is", or do they "pre-process" it, and do things like build in struts to protect hanging bits, or put a cage around to protect sticky-out bits, or even put a honeycomb for large internal hollows? Or do they just "print and be damned", leaving it to the maker to fix his 3D source if it breaks during printing?
  — They print in a self-supporting resin powder matrix, so support struts aren't necessary.
  They do offer the capability to create a sinter-shell around your model to protect delicate projections and keep separate bits together in transit; it hasn't been an issue for me.
  I know they've been known to fiddle with separate component placement though; I read a complaint from a guy who had a bell printed outside his belltower instead of hanging inside. That sort of complaint is pretty rare though, in fact it's the only one I'm aware of.