Shapeways seems to want to blame it on your sprues. I sent an inquiry and told them about the issues some of them had and asked if I could pay the difference and just get them individually, instead of on the sprues. Here was their response:
APR 22, 2013 | 10:54AM CEST
Mitchell Jetten replied:
Dear Joshua,
Thank you for reaching out to us.
Unfortunately the loss of detail and roughness is caused by the technique used for 3d printing Frosted Ultra Detail.
One of the sides will have support material stick to the model which is used to print your model.
Unfortunately we cannot change the design of the Biker pack as we are not the designer of the model.
Shapeways only 3D prints the models which have been uploaded by independent designers.
I would like to ask you to go to the model on the website and click on the Contact Designer button.
This way you will be able to contact the designer directly and ask him if he is able to upload the model without the sprues.
Again my apologies for the inconvenience.
Best,
Mitchell
Kind regards,
Mitchell Jetten
Customer Service Agent
www.Shapeways.com
Mind you, Mitchell didn't even answer my question, but he wasted no time in blaming the problem on your sprues. I believe you when you say that you've had good results from some of them on the sprue, and am not trying to say that you're mistaken. Just letting you know what Shapeways is telling people.
Funny, Mitch never had the balls to tell me that when I dealt with an issue illustrated in the casting 411 thread. He's taking advantage of the fact you haven't ordered them singularly and got similar shitty results. I have.
Honestly, Mitchell doesn't know a damn thing and is only really good at picking apart a small detail in an email. When they actually take the time and file an inquiry with the production team, different answers do arise.
I only do the sprues because its the only way I can make it somewhat affordable. I can't magically make Shapeways make their FUD affordable, much less actually care about it like they do with their damn color sandstone. My hands are pretty much tied on the matter.