Preform 1.5.2: slicer fill display question/mystery


I’m still getting my bearings understanding how Preform represents holes vs fill vs empty space when viewing slices.

I’m working on a model that Preform says it successfully fixed on load (I knew it had some isolated issues, but I thought I’d see if Preform’s integrity checks would handle them).

In an area unrelated to the ‘bad geometry’ that was fixed on load, I am seeing some strange (wrong?) representation when previewing slices. Basically it seems like the slicer gets confused about what is inside and outside of a piston. The piston itself is solid, but the slicer seems to think the outside of the piston is the solid part.

Since I’m not sure how to read the visual cues in the slicer, I could be wrong. But if you look at the attached pic you should see cross hatching surrounding the circular piston slice at mid screen. This section is ‘open air’ in the model and so should not get filled… if that is what Preform is indicating will happen.

As I progress through the slices, it is clear that the interior area of the circular piston is empty. Other pistons on this ‘leg’ are shown solid (similar to the surrounding walls you can see in this picture). Based on that, I assume some is amiss, even though the geometry is clean and solid for the piston. (verified in meshlab).

Any insights would be appreciated. Lacking any thing else I may delete the piston and redo a test to see how that will work, but after putting in all the supports, it would be a shame to start all over again.

NOTE to self: inspect slices thoroughly before building in supports! :smile:

Thanks all,


It definitely looks like PreForm slicer is not interpreting your geometry as intended.

What software did you use to export the models? I have seen this kind of behavior emerge for multiple bodies intersecting with zero-thickness spacing or with features < 0.1 mm. Exporting your model to STL/OBJ in a different manner could help.

Thanks Craig,

I am cleaning up (and breaking apart) the part a bit to see if I can isolate the problem to something more simple.

My export process is pretty basic - coming right out of blender to STL - checked in meshlab and my own software. I did find a two faces flipped so I am retesting and will let you know what I find.

One quick question - I DID scale up the stl quite a bit in Preform - 25.0 in xyz, as the units in blender were probably meters or something. Given that I did that INSIDE preform, is there any chance that the slicer is still operating on the non-scaled version of the geometry (seems unlikely, but I figured I would ask). I could scale it up in Blender, but I did not figure that should make a difference.

And a wish… I do see that Preform is offering to do some fixing for me on load. I would love to see some basic diagnostics in a console printout or something just to indicate what it did. (filled holes, flipped faces, etc). I’ll put this on the preform wish list.

Thank you!


Yes; the slider works on the manipulated (scaled, oriented, etc) version of the geometry.

Any better results with a differently exported model?

Maybe try manually stepping through the original and look for something like zero-thickness geometry. That would probably cause confusion and maybe what you are seeing.

Still not able to diagnose the problem definitively. I have cleaned up the geometry and removed self intersecting parts and I have isolated the problem to a single part. It is ‘manifold’ but also pretty thin (but hard to tell how thin is too thin - would love to have a way to visualize that a bit. ) still the slice gets confused at the same location (even with the piston removed). I will do a bot more checking including in netfabb as suggested to see if I am missing something.

The information displayed by the slicer is what is used to actually print the part. If it doesn’t look right, don’t print it, and check for possible issues in the original STL. Usually, these issues are related to non-manifold geometry. It could also be related to multiple adjacent meshes (aligned right next to each other (with an infinitely small gap). In these cases, try to merge them into one mesh in your original CAD software, or make them overlap slightly.

Thanks All. It looks pretty clearly like I have some hosed geometry that I somehow missed prior to loading in Preform. Will verify fix in Netfabb and report back if problems persist, but I expect they will not.