Note: following these guidelines won't guarantee printability of all models, but 95% of models should pass with these rules applied. Of the 5% of models that still may fail, we will try to reprint once. If that fails, we will notify the customer that their model is unprintable. We will also add that model's reason for failure to our list of design rule changes to review.
Wall thickness should be 3 mm or over
No movable parts are allowed anymore. Movable parts are interconnecting pieces (think: chainmail) or piece(s) freely moving within a piece (think: a baby rattle, the beads inside are freely moving in the rattle)
Parts are accurate within 2 mm of the design. Depending on how much binder is deposited, parts may shrink or grow slightly during the printing process. Binder deposits should vary depending on the geometry of the Shape in a build. Since Shapeways prints a variety of shapes in one batch, some parts might come out inaccurate.
Clearance between near touching sections should be at least 3 mm(think money belt). This distance will help achieve consistent gaps with duplicate prints
Self Support! Designs that are thin need to be supported structural so they can support themselves.
When you design, ask yourself this question: if I made this out of wet sand or brittle clay, can I lift the design without it breaking? If the answer is "no," then your design will likely get rejected.
The Problem Bird inside cage is too heavy, it would fall and crumble.
The Fix Bird could be hollowed out which could help. (Also the wire cage cross-section needs to be 3mm.)
Here are a few more theoretical examples...
The Problem The stem is too thin to support the round structure at the end, which will break off. The Fix The stem would need to be 3mm thick, though in reality this also depends on how big and heavy the ball is at the end of the structure.
The Problem Imagine if this was a web structure somebody wanted to make into a 3d model that curved in all 3 dimensions. This model is fragile and would crumble.
Think of it this way, imagine a spider web--if you tried to move a spider web, it would break. The same with this piece.
Why will it break? What's the green state?
Stainless Steel powder is deposited layer by layer. A printing head also deposits a binding material. This binder solidifies what will become your product. After your product has been built up it is gently lifted out and put into an oven. At this stage your product is still very delicate brittle and porous (this is the Green State). See the clip below for an idea on how brittle this green state is.
The product is then infused with bronze. The bronze permeates your entire product and solidifies it. Next, your product is 'fired' in an oven. At very high temperatures, the metal particles fuse together into a solid object.
After firing, the object is cured. Later the outside of the product is sanded and polished mechanically by tumbling. See here for a video on the process: