Advanced Post Processing of STLs for 3D Printing

Looking to get the most out of your 3D prints? Here’s our guide to optimizing STLs before they’re sent to the build chamber.

A few weeks back I wrote about the process of exporting CAD geometry to an STL file that will be processed by a 3D printer. While exporting is a critical step in bringing your project to life, there’s a lot more that can be done to ensure your design emerges from your 3D printer in pristine condition.

In this article I’ll review some of the most common problems with .STLs and suggest a few ways to optimize your model and deliver the best print results.

It’s Got to Be Watertight

3D printing, like other manufacturing techniques, is made for building solid objects. While that might seem obvious, there can be a disconnect when it comes to .STLs.

When you go to export an STL file your CAD package actually captures your solid model and translates it into a series of non-uniform triangles. In its triangulated form your model can then be processed by a printer and rendered into g-code—the language used to lay down the material that eventually becomes your object.

The problem with the translation from solid object to triangulated representation is that sometimes your CAD package will miss some of these triangles, leaving holes in your model. Where there are holes in your model the 3D printing process can go haywire, ruining your job and wasting expensive material.

That’s no good.

It’s Good to Be Normal In 3D Printing

Another thing to worry about after your model has been triangulated is whether the orientation of the normal vectors in your triangles is correct. If your triangle has misaligned normal vectors then your printer won’t be able to distinguish between the inside and outside of your model’s surface. This can lead to strange anomalies in a print, such as surface abnormalities, holes and generally undesirable results.

Strong Walls = Strong Prints

As was mentioned earlier, 3D printers are in the business of building solid objects. That means that every built object has to have a wall thickness. Depending on what printer you’re using, there will be a minimum wall thickness that is required for an object to be built. In most instances this minimum thickness requires a few millimeters of materials to form a solid object.

If your print has walls thinner than your printer’s minimum thickness, your printer won’t recognize them as printable. This type of error can be catastrophic for a build.

Units, Units, Units

Lastly, before you ship your model off to the printer make sure you know what type of units you used to design your model. There’s nothing worse than receiving a model that’s been printed either too small or too big. Always remember to check your units.

How to Fix Common STL Errors and Achieve Perfect 3D Prints

Now that we’ve reviewed the most common errors (and they are very common) when working with .STLs, it’s time to learn about the fixes.

In the end, many issues that face .STLs are imperceptible to users. To find them and fix them you’ll have to use software to perform an audit. While there are a number of software options that have incredible tools for fixing .STLs, they’re probably overkill for most applications.

Luckily, there are number of free, cloud based services that can perform a thorough audit of your .STL and repair it if necessary.

For my part, I’ve found that netfabb and willit3dprint are excellent options for people that occasionally prototype. If your prints are being built with an eye to critical design reviews or end-use applications, however, a more sophisticated, hands-on software like Materialise’s Magics or 3D Systems’ Geomagic Design X might be right for you.