STL files are the most common file type for models designed for 3D printing. If you’re trying to work with STL files within SketchUp, you’ll find it challenging because all of the faces are subdivided and there are a ton of extra edges throughout. In this article, I share my tips for working with and modifying STL files so you can 3D print them.
But what if you want to make some changes to the model? If you open it in SketchUp, you’ll probably notice a lot of problems with the STL file that make it really difficult to edit. Things like subdivided faces, (Edges that divide a face into multiple faces, even though they are on the same plane), make it impossible to use the Push/Pull tool on a surface. Many times they are missing faces altogether, or extraneous edges acting as prison bars over any holes or cutouts in the model.
I built a MendelMax 1.5 3D printer, which is an open source 3D printer. (UPDATE: 4/13/15 – I’ve now upgraded to a MendelMax 3. Check out my review video here.) That means all the plans and instructions on assembling one are available for free online so you can build your own. While my printer works, I still only consider it 80% complete. There are improvements I am continually making to it in order to turn it into what I consider to be the ideal printer.
One of the things I wanted to add is a filament spool holder. Filament is the plastic that gets fed through the heated extruder nozzle and prints the objects layer by layer. As you’re printing something, the filament needs to unreel from a spool, so most people use some sort or spool holder. I found a really cool filament spool bracket on Thingiverse that I liked, so I downloaded it and printed out a pair.
While I really liked the design, I didn’t like that I would have to disassemble part of my printer in order to bolt the brackets on. Also, with different width spools, I would have to adjust the bolts every time I wanted to put a different spool on. So, being lazy, I resorted to using spring clamps to hold the brackets on. How elegant!
I then discovered this other model of a clip designed specifically to clip onto the aluminum extrusion I used to build my printer. So I thought, why not combine the clip with the bracket, so I can ditch the spring clamps and easily slide the brackets to match the width of different spools?
Importing STL files
The first step to working with STL files in SketchUp is to download the STL plugin from the extension warehouse. If you don’t have the STL plugin yet, open SketchUp, and go to Window -> Extension Warehouse, and search for “STL”. It’s the one made by SketchUp Team named “SketchUp STL”.
You won’t be able to open STL files directly, rather, you have to import them into an existing file. So just create a new model, go to File -> Import, then be sure to change the file type to “STereo Lithography Files (.STL)”, or else you won’t be able to see the file you’re looking for.
Cleaning Up STL Files
If you read my article on the Best Plugins for 3D printing, you’ll know that I like using the “Solid Inspector” plugin by ThomThom. He makes another great plugin called “Cleanup³” that does a good job at getting rid of extra edges and attempting to repair missing faces automatically. You can find this plugin on the Extension Warehouse as well.
Once the plugin is installed, you just go to Plugins -> CleanUp³ -> Merge Faces. That will attempt to get rid of any subdivided faces and make them whole again. Another task you can run from the plugin is Plugins -> CleanUp³ -> Erase Stray Edges, and that will attempt to get rid of any extra edges in your model.
UPDATE: 3/24/14 Thanks to Marcus Ritland, he pointed out that you can merge coplanar faces directly inside SketchUp. While in the Import window, click Options, and check the box “Merge Coplanar Faces.” Thanks Marcus!
You’ll notice that I say the plugin will attempt to fix the model. I say that because your results will vary depending upon how bad the STL file is. STL files are created differently depending upon the software it originated from. Sometimes, if the model is really bad, I’ll just model it from scratch, using the STL for dimension references in SketchUp or by copying specific profiles from the model.
I imported the clip STL that I’m going to combine with this one, and processed it with the CleanUp³ plugin as well.
Editing the Model
In this model, I wanted to take an existing filament spool holder, and combine it with a clip that would allow me to clip the spool holder in place instead of bolting it in as originally designed. So essentially, I’m combining two models into one.
The CleanUp³ plugin worked really well on the main face of the bracket, but there were still some subdivided faces that weren’t repaired so I chose to redraw the bracket. This is actually really easy when you have a model that consists mainly of extruded profiles, such as this one.
- I copied the face of the main profile by selecting it, then using the Move tool with the CTRL key to make a copy of it. I tapped the left arrow key on my keyboard in order to lock the copy along the green axis as I moved it.
- I then did the same thing to the clip, copying the main profile of the clip in order to combine it with the bracket. Instead of aligning the copy with the original, I just copied it out into a temporary location, and then turned it into a group. The reason I turned it into a group is because I know it’s going to take a little bit of maneuvering to get the clip profile positioned just right on my bracket, and I don’t want the edges sticking to one another while I’m adjusting things.
- Using the Move tool and Rotate tool, I adjusted the clip profile to the position I wanted it. I then made a copy of it for the other side and made a few changes to it in order for the bracket to work once it’s printed out.
- At this point, I’ve got the clips positioned where I want them, so I’ll right click each group, and select Explode. This will remove the group and merge the entities with the bracket profile. I’ll then finish cleaning things up by deleting some of the dividing edges so I am left with one complete face.
- Using the Push/Pull tool, I extruded the new profile, referencing a point on the original model to match the thickness. (This is why I made sure I locked the green axis when I created the copy, so I knew it would be aligned with the original and I could reference it for different dimensions.)
- I then completed the model by copying the profile from the flange of the bracket, and extruding that as well. I noticed the original brackets that I had printed out were a little flimsy so I added some gussets as well to provide greater strength.
Checking and Finalizing the Model
Before trying to export the model, I recommend using the Solid Inspector plugin to check for any missing or extra faces/edges. I’ve set up a custom shortcut in SketchUp so I just press SHIFT S for the Solid Inspector.
Your model needs to be considered a “solid” in order to export an accurate STL file. One of the common problems is having extra faces on the “inside” of your model. The Solid Inspector can find these for you, but it’s a little tricky to delete them since they are on the inside of the model. One trick I use is (once again) using custom keyboard shortcuts to make the process much easier. I assign the letter N to Hide, (can also be found in Edit -> Hide). Then, I have the letter J assigned to Unhide Last (can also be found in Edit -> Unhide -> Last).
So what I do is select a face, tap N to temporarily hide it, and that lets me view the inside of the model and delete the extra faces and edges. Then, I just tap J and the hidden face reappears.
Exporting the STL
Finally, we are done editing and checking the model, the last step is to export it as an STL in order to print it out. I like to orient the model before exporting it so I know it will print out properly, even though most 3D printing software has the ability to rotate objects.
To export, go to File -> Export STL…, select the appropriate unit of measurement, and click Ok. (I honestly don’t know the difference between ASCII and binary, I just leave it on ASCII and it works for me.) When you save the file, make sure you add the .stl file extension at the end of the filename. I’ve had some trouble with the extension not appearing, and Cura can’t find it when I try to load it.
Then, go ahead and print it out and see how it works!
Once you’ve printed out your part, help the community and upload it to thingiverse and share it with other people.