Blender wall width problem

So I uploaded my first file to Shapeways recently as an STL exported from Blender. The object has a 0.7mm wall width which is the print minimum but a day later I got an e-mail from SW saying the file could not be printed because the wall width was 0.55mm. I had defined the width in Blender using the solidify modifier and was careful to set my units to metric. I went back and compared the dimensions for the whole object in Blender against the dimensions SW gave me when I uploaded the file and they differed by no more than 1/100th of a mm. Very confused as to why SW thinks my wall is 0.15mm thinner than I designed it.

If anyone else has had a similar issue or could offer some insight I'd be very appreciative!

Check your STL file with netfabb studio basic - first see if you get the warning triangle on import (showing that there is something amiss
that needs repairing - an action that shapeways' software tries to do automatically on upload but which might change your model slightly),
secondly use the measuring tool to repeat the measurements as shown on the rejection image. The upload checks may have removed an overlapping face, making the wall thinner, or the shapeways employee doing the checking may inadvertently have picked a small object
on the wall instead of measuring wall thickness.

The solidify option in Blender actually messes up in this manner quite often. In particular, it doesn't handle sharp or angled corners well.
There is an option on the Solidify modifier to set the "Crease Angle" - that is supposed to help prevent the situation you are describing, but I have yet to figure out the exact settings to make it work right. I tend to add about 10% to the desired thickness to help reduce the issue.

If you don't already have it, grab a copy of Netfabb Basic from www.netfabb.com
With that tool, you can go around the model measuring the wall thicknesses the say way that the Shapeways checker does.

Thanks guys! Stonysmith, I'll definitely experiment with the crease angle though from the rejection image it appeared they weren't measuring it at a corner. May just have to add some padding as you suggested.

I did get Netfabb but when I open the STL in there it seems to think the entire object is 1/100th the size it is in Blender. Maybe it's reading meters as mm? Not sure how to fix this.

In Netfabb, click on Part/Scale, and you can scale it up to any size you wish.

Thanks!

When you said "metric units" did you mean "metres"? Or maybe Blender shows mm but works with "computer number 1.0" = 1 metre, thus 1 mm is stored a 0.001 internally? Formats & programs assuming such approach is good but ignoring the concept of precission are not rare (yes, .wrl, you are guilty as charged, but not alone).

STL files are 'agnostic' (or is that ignorant?) of units. In Blender 1 Blender Unit = 1 unit in stl - that's why when you upload an STL to SW you have to specify which units to use.

It seems it also can be a problem if the absolute size of your model is too small. This is definitely a problem in Sketchup and seems also to cause issues in Blender (I discovered today). Perhaps this thread is also interesting? https://www.shapeways.com/forum/index.php?t=msg&&th= 17035&goto=80396#msg_80396

Here is how i use solidify with precision and without too much problem:

1. apply scale for object
2. consider thickness in mm
3. activate EVEN THICKNESS and high quality normals in modifier.

This way if i set 1 mm thickness i have 1mm everywhere. Only problem is that it sometimes does not work as you would imagine. In that case i work more manually...