The printing techs reorient models in order to get the best "yield" per print job. They gang many different orders for the same material into a single print job and they reorient the various models to optimize the use of the material in the print volume. So even if you submit a model of say a gear that has the gear profile in the XY plane (generally considered to be the print plane) it may be reoriented into the XZ or YZ plane in order to achieve better job utilization. The Z axis or layer step axis is in my experience less accurate because it is not as fine as the XY laser scan layer. As a result features that you want to be round such as holes can come out oval.a voxel is a three dimensional pixel
Shapeways keeps hinting that user-selectable print orientation is coming, but it's still not here yet. I'd gladly pay extra for that option, but I don't know how much they would have to charge to make it feasible.http://www.fireballmodels.info
I have requested and would gladly pay a reasonable surcharge for an orientation selection option.
I suspect that either Shapeways and/or the printer vendors are working on software to automate optimization of print volume utilization. As the volume of printed parts climbs this should get easier as the optimization can span several print volumes. It would be both an interesting and challenging problem to work on.a voxel is a three dimensional pixel