I wrote a bit about WSFP in Greg's Micro Master Pentultimate thread here:http://twistypuzzles.com/forum/viewtopic.php?p=287292#p287292
There's no way they could tumble it.
As for extra parts, for really tiny parts there seems to be a higher chance that Shapeways loses a few but the chances are still rather low.
Shapeways does sometimes lose big parts and sometimes there is a print flaw in just one or two parts (a bubble or the parts gets truncated or various other issues).
If I had my way, I'd like to see 1 extra part for each piece type for any piece type with 8 or more pieces. If I really got my way I'd like to see 1 extra piece for every 20 or so (and round up if it's close to .5).
So that would be:
6 pieces: no extras
8 pieces: 1 extra
12 pieces: 1 extra
20 pieces: 1 extra
24 pieces: 1 or 2 extra depending on size
30 pieces: 2 extra
60 pieces: 3 extra
And if it's a really small piece, include 2-3 more on top of that.
Yes this does increase the cost by between 5% and 10% but it's worth it (at least to me). I'm also okay with the designer passing this extra cost onto me rather than taking it out of the markup.
There are multiple reasons to include extras including:
- Shapeways loses the pieces
- The piece has a print flaw
- You break the piece during assembly
- You lose the piece in the sorting / counting / tumbling / dying process
In all fairness though, Shapeways doesn't screw up that often and when they do, they're always willing to make it right, even if it takes a while.