Update: 19 Jan 2018

The original page – shown below the line of dashes – talks about STL files, the problems different slicers have with them, and ways to fix the problems. Recently a new web based STL file repair service has become available that seems to be highly effective. Here’s the link to the service: click here for the web page.

Note that even though this  service is provided by Netfabb, it does work differently from previous versions of both Netfabb, the Microsoft online repair service, and the 3D Builder application that is part of Windows 10. “Differently” means it is able to fix STL file the others could not fix.

In particular, this new service is able to fix the difficult problem of overlapping shells. Most slicers will fail if they are given an STL file with overlapping shells because they can’t determine what is the inside and what is the outside. But I have been able to fix several overlapping shell STL files that were previously impossible to print. But after running them through the new Netfabb service they slice and print fine.

I was unable to successfully slice the following STL file with any slicer until after I fixed it with the new Netfabb service:

Loading file

You can download this file here or here.


Before anything can be 3D printed the GCode file that drives the printer must be generated by a slicing program. This means, of course, that the slicer has to be able to process the input STL file successfully. And a crucial issue for this is the basic nature of STL files.

Specifically,  a precise definition of what constitutes a correct STL file has yet to be established. The net result of this is that different slicers can produce different results from the same STL files, and there is no good way to determine what those results might be ahead of time.

Different Slicers 

I have 3 slicers that I use on a regular basis: Craftware, Simplify3D, and the Prusa version fo Slic3r which I call Plic3r. Of these I try to use Craftware whenever I can, but I defer to Plic3r when Craftware produces incorrect results. I find that Simplify3D is the least reliable of the three.

Repairing STL Files 

Be aware that the parts I slice are all produced using the same software: Rhino3D and it’s Grasshopper add-on. Almost all of the parts I design are large and have fairly complex geometry, and I am aware that Rhino has some problems/quirks with it’s STL export process. So I always check for naked edges and non-manifold definitions. I usually run Rhino’s STL files through the 3D Builder application that checks for invalid STL files and then uses the NetFabb algorithms to correct them.

I have often found that a file 3D Builder says is good is found by Plic3r to still have errors. Sometimes Craftware will slice such an STL file properly, but sometimes not. Plic3r has an STL repair facility built in to it, so by running the STL file through that and then re-saving it, Plic3r will slice the result OK. Sometimes Simplify3D will still slice a corrected file incorrectly, even after it has been fixed by both 3D Builder and Plic3r.

As I write this Craftware has just released it’s 1.15 version and is still making updates to it. 1.15 uses a new slicing engine so it’s a bit too early to comment about it’s results, but in general the new version does resolve several problems Ver. 1.14 had. Initial testing shows that 1.15 slices many STL files OK, but does have problems with the more complex ones, even though no slicer complains of errors in the STL files.

Slicing Results 

I’ll use this STL file as an example of these issues: Holeylayers2. Here is what the part looks like:

I printed this part after slicing it with Plic3r. Prior to slicing I ran it through 3D Builder’s repair function and the STL repair function in Plic3r. The results from Plic3r slicing look like this:

This is the complete part; it is a table lamp designed to hold an LED light at the bottom. This image shows how the inside of the lamp looks:

As the Thingiverse page shows, the part printed OK (although like most complex parts it takes a long time.)

But what about the other slicers? The results are not so good. Here’s what Craftware Ver. 1.14 does:

This looks OK, but wait! Here’s what the inside looks like:

See that solid layer that completely covers the inside? That’s wrong, and there are several of them. So even though this version of Craftware slices the part OK, the results are useless.

In Craftware’s defense I should say that there is a newer version of the software that has just been released – Version 1.15. This version still has bugs and the Craftware developers have said they will be releasing updates at a fairly rapid pace. So hopefully a newer version will resolve problems like this.

So now, how about Simplify3D? The most current version, 4.01, loads and slices the STL file OK and the results look like this:

Do you see the problem?  Here’s a close-up view:

Simplify3D puts big gaps between the holey layers that are not there. These gaps would cause the print to fail, so again, these results are useless.


It may be that there is still something wrong with the Holeylayers2 STL file, but 2 different STL correction tools have said it is OK, and one of them slices it OK.  So my sense is that there are major differences between the internal workings of different slicers, and therefore you should switch to a different slicer if you encounter a slicing error with a particular STL file.

Last Update: 21 Dec 2017