The flaws can be impossible to find without a proper diagnostic software analysis.
The floaters were not the primary flaw- they were the render-able geometry left behind by a boolean or trim/stitch operation that resulted in non-solid geometry.
This might have resulted in duplicate points or polygons or line segments that perfectly coincide with other points, polygons or line segments.
Some of these bits of unconnected geometry or topology might be internal to the model… And most of these kinds of error will occur when you convert the file from a surface model to an STL model on export.
Something as silly as modeling in a space with a resolution of 0.0001 mm - but converting to or importing into a model space with a resolution of 0.001 mm can result in points in the modeling space being “Averaged” to the exact same coordinates… giving you two points in the same location, connected by line segments of zero length- either of which can give printers conniptions trying to figure out the shape of the object.
Just one polygon in a model that has its defining points connected in reverse direction creates a “hole” in a model that renders as a solid, but as far as the printer is concerned is a soap bubble with a wall thickness of zero.
Most of these errors are due to bad procedures or set up of a modeling space by modelers who do not understand solidity in 3D modeling, and therefore do not realize the kinds of things they might do that will violate solidity.
People who model in surface modeling apps like Solidworks, Maya, Rhino, or SubD apps like zBrush and Modo are far more prone to bad modeling technique, because the Apps themselves are designed to represent surfaces only and do not warn you when your model is not a solid. And so there is no pressure to learn what solid modeling is.
I can’t tell you how many jobs I’ve gotten where some really brilliant artist modeled a ZBrush figure with oodles of delicious detail… and the file gets handed to me because the artist did not make a model that could be realized as a solid object. ( a LOT of digital modeling if for CGI animation… or games… and does not NEED to be a solid- it just has to render nicely.)
Apps Like Meshmixer were largely originated as a tool for resolving the many different kinds of meshes produced by the many different types of modeling apps out there.
Preform itself has an import function meant to detect and correct many kinds of non-solid geometry- but it can not handle every possible combination of errors that modeling apps can produce…
And even though I run an app that ONLY can produce a perfect STL solid… Preform often claims that a model I import is broken… even though it is a perfect qualified solid.
The easiest solution is to spend the money to buy an app that models in voxels and can not export an STL that is not perfect… Like Freeform or its less costly cousin Sculpt from 3D Systems.
Failing that, the second best option is to use a modeling app that has solid modeling features, diagnostics and repair features such as Form Z.
And, of course, its better to read up on how Topology differs from Geometry and how the two have to be configured to achieve solid geometry.
For example- Imagine 8 points in space in the configuration of the apexes of a Cube.
That is the geometry of the model.
But HOW are those 8 points connected to each other? If each is connected in straight line segments defining the vertices of a cube- then you have a solid model of a cube.
However, if one of those corner points is connected to the diagonal opposite corner point thru the center of the cube… that can not describe a cube… can it? Those specific order of connections are the Topology of the model, and they must be in a very specific order for the computer to be able to understand the geometry as a solid cube.
In subD modelers you use 4 point geometry- meaning every polygon is supposed to have four points.
However- if One of those 4 points gets moved out of plane to the other three… then that polygon is NOT a flat plane anymore… and it will often render with a triangular ‘hole’ in the polygon. This violates solidity…
and, of course, STL conversion seeks to bisect every 4 point polygon into two triangular polygons because 3 points ALWAYS define a flat plane.
Yet- if one of those triangles is connect in the reverse direction to all the others, then its a hole into the model and it can not be a solid.
Some of these simple things Preform can correct for. Sometimes, in trying to correct bad geometry, Preform itself can create unprintable geometry… without being able to ‘recognize’ that the model its is displaying is a Ghost the Form 2 can not print.
3D modeling has become popularized… lots of folks get into it with no real training or background in how it works- they rely on software engineers to come out with apps that correct their mistakes without their even having to be aware there was one. And so those modelers do not improve in their technique.
There is no substitute for competence. And in the world of 3D printing… for every failed print that is the fault of the printer or its materials… there are 50 that are the fault of bad geometry in the model.