How to Fill Holes in STL Files for 3D Printing


If you find yourself with an STL file that has some holes you want to close up, and you don’t know what to do, I wrote this article to help solve this problem.

Keep reading for more info.

How to Fill Holes in STL Files for 3D Printing

If you have an STL file with a hole that you want to fill before 3D printing, it can be done using Meshmixer.

Meshmixer is a free to use 3D modeling software, which is available for download online.

These are the two main methods we will be detailing in this article, which you can use to fill holes in STL files:

  • Auto Repair Method
  • Make Solid Method

Auto Repair Method

Check out the steps to fill holes in STL files using the Auto Repair Method:

  • Load STL file in Meshmixer
  • Select the Inside of the Hole
  • Delete the Hole
  • Use Auto Repair Function

Load STL File in Meshmixer

First off, you’ll need to load the desired STL file in Meshmixer. It is a 3D modeling software that allows you to modify the file.

This is a great software that can help you not only filling holes in STL files but modifying all sorts of things you may need with great ease and an intuitive approach.

Select the Inside of the Hole

After loading the file you want to fix into Meshmixer, the next step is selecting the inside of the hole.

How to Fill Holes in STL Files for 3D Printing - Interior of the Hole Selected - 3D Printerly

To do it, select the entire inside of the hole. You’ll do that by clicking on the parts you want to select.

If you inadvertently select other parts, don’t worry, hold the shift key down and deselect them. Before moving to the next step, make sure that you only have the hole selected, so orbit around your object to be sure nothing else got accidentally selected.

If you’re trying to select a hole on a curved object, then turning on the transparent shader option might make it easier for you to select only the right parts.

That way, your model will be transparent, and you will be able to see it from every side, helping you select the interior of the hole.

Delete the Hole

With the entire hole selected, you will now delete it by simply hitting the delete key.

How to Fill Holes in STL Files for 3D Printing - Deleted Hole - 3D Printerly

If you accidentally delete the wrong part, you can press undo to solve it.

If for some reason that control does not work, load your model back up and make sure to only select the interior of the hole, if any other part is selected as well that can lead to problems on your prints.

Use Auto Repair Function

The next and final step of this method consists in using the “Auto Repair” function on Meshmixer.

How to Fill Holes in STL Files for 3D Printing - InspectorAnalysis - 3D Printerly

To find that function, go to “Analysis” on the left side toolbar and then choose the first option, “Inspector”, and you’ll find the auto repair function.

How to Fill Holes in STL Files for 3D Printing - Auto Repair Function Location - 3D Printerly

Click the “Auto Repair All” and wait for the hole to be filled. You can even check with the transparent shader, to make sure the hole was filled on the inside as well.

How to Fill Holes in STL Files for 3D Printing - Auto Repair Filled Hole- 3D Printerly

A lot of users recommend this method and think it works wonders to fill in holes of STL files. One user prefers this method over the “Make Solid” one as this method won’t reduce the quality of the objects.

Check out the video below to learn more about filling holes in STL files using the Auto Repair method.

Make Solid Method

Check out the steps to fill holes in STL files using the Make Solid Method:

  • Select/Delete the Hole
  • Make Solid
  • Change Mesh Density
  • Delete Older Version

Select/Delete the Hole

With the STL file that you want to fix loaded into Meshmixer, you’ll need to select the interior of the hole you want to fill.

How to Fill Holes in STL Files for 3D Printing - Interior of the Hole Selected - 3D Printerly

To do that, click on the interior of the hole from the model and leave it selected. Then delete the hole like in the previous method.

For that, hit that delete key with the entire hole selected. If you select anything that should not be deleted, hit the undo to go back.

How to Fill Holes in STL Files for 3D Printing - Deleted Hole - 3D Printerly

Make Solid

Now, with the hole you want to fill deleted, you’ll need to use the “Make Solid” function.

How to Fill Holes in STL Files for 3D Printing -Make Solid Function - 3D Printerly

For that, go into the “Edit” section of the left toolbar and then click on the “Make Solid” function.

Meshmixer will check for any errors, then it will lead you into a menu where you can change different settings, including mesh density, which will be our next step.

Change Mesh Density

After deleting the hole and going into the “Make Solid” function, your object should be filled. You’ll now change mesh density of the model.

How to Fill Holes in STL Files for 3D Printing -Mesh Density - 3D Printerly

This allows you to preserve or to lose detail. If you bring the mesh density down and hit update, it will leave your print with a lower quality.

If you bring the slider up, it will make it smoother. Once you are pleased with the mesh density of the model, click accept.

Delete Older Version

After accepting the “Make Solid” function and changing the mesh density over at the previous step, your model should be ready.

On the object browser, on the bottom right of the screen, you’ll see now there are two separate objects.

How to Fill Holes in STL Files for 3D Printing - Object Browser - 3D Printerly

One of them will say “solid” and the other one will not. You can delete the older version, so you won’t get mixed up, so you’ll just keep the solid one.

The “Make Solid” function is useful to remove any weird geometry you may have added along when modifying your STL file, so it has a lot of uses besides filling holes.

A lot of users suggest this method to fill holes in STL files as it is very quick and is done in a few clicks.

Check out the video below to learn more about filling holes in STL files using the Make Solid method.

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