Change Infill Density in a Specific Section on a 3D Model for 3D Printing.




Introduction: Change Infill Density in a Specific Section on a 3D Model for 3D Printing.

About: Madeira Island Civil Engineer 1983

This is a simple tutorial where I will compare a powerfully functionality that two available slicers have.

A slicer is a tool you will need to convert a digital 3D model into printing instructions for your 3D printer.

The first one is a free, open-source software - Slic3r (S3r), and the other one is Simplify3D (S3D), a commercial/professional solution for 3D printing.

I intend to demonstrate the utilization of an advanced feature in order to give more strength/rigidity in a specific region in your 3D model. Doing this I will avoid to increase the thickness of the 3D model and will guarantee that the model will resist to the applied loads.

Basically the final 3D printed model will have different infill densities depending on the region of the model.

The workflow was based in the following processes:

  1. 3D Modeling - create the 3D model
  2. 3D Simulation - understand the regions the are more fragile in the 3D model
  3. Split 3D Model - subdivide the 3D model into that specific regions
  4. Slicing - generate S3r and S3D toolpaths
  5. 3D Print - materialize the digital 3D model

The software for 3D modeling/simulation was the easy to use Fusion360 (Autodesk), and the 3D printer was the versatile BEETHEFIRST from BEEVERYCREATIVE.

Step 1: 3D Modeling

The purpose of this 3D model was to create a filament holder for 750gr filaments spools, that will be fixed in the back of the 3D printer - BEETHEFIRST.

In this step I will only show some pictures of the final 3D model.

Step 2: 3D Simulation

After the 3D modeling a study simulation (Finite Element Analysis - FEA) was conducted in order to analyse the 3D model and understanding the sections of the model that must be reinforced.

(1) In Fusion 360 we need to change from the MODEL to the SIMULATION workspace.

(2) Create a new simulation STUDY.

(3) Choose Static Stress, and check:

  • Settings
    • Mesh
      • Create Curved Mesh Elements
      • Use Part Based Measure for Assembly Mesh

To proceed with a FEA simulation we need to define three main attributes in our study:

(4)Structural Constraint - in this case will be the chamfers in holes

  • Type: Fixed
  • Axis: Ux Uy Uz

(5)Structural Load - 10N (1Kg - since the filament spool has 0.75kg)

Select the section where the force will be applied

  • Type: Force
  • Targets: 1 face
  • Magnitude: 10N


  • automatic contacts

(7) To confirm if everything is okay, see the color of the traffic icon, if it's green light means there is no issues found, now you will be able to run the simulation based on settings that you selected, just click in the traffic icon.

(8) The default view of the simulation is the Safety Factor, let's change to Stress and analyze the regions that are more affected by the applied force.

(9) As we can see there are three main regions that are more stressed, these will be the regions that must be reinforced.

Step 3: Split 3D Model

In this step, I will show how to prepare the 3D model in Fusion 360 to be sliced in S3r and S3D in order to allow those specific regions to have more strength.

After identifying those specific regions, we need to split the final 3D model in various parts.

(10) Create a Box that intersects the stressed region.

(11)Combine the Box with the main part.

  • Target Body: main part
  • Tool Bodies: new Box
  • Operation: Intersect
  • New Component: check
  • Keep Tools: uncheck

(12)Combine again the new body with the main part, this time we will make a cut operation.

  • Target Body: main part
  • Tool Bodies: new Box
  • Operation: Intersect
  • New Component: uncheck
  • Keep Tools: check

Repeat (10)(11)(12) for the other regions.

(13) Final 3D model with the split parts.

(14)(15) Save each parts separately from the main bodies, in the end you will have 3 split parts and the main bodies (or what's left of it).

Step 4: Slicing - Slic3r

With the 3 split parts and the main body now we can proceed to the slicing process. I will demonstrate first with the Slic3r, the free-open source software.


Main print settings:

  • Layer height: 0.2 mm
  • Vertical shells
    • Perimeters: 2
  • Horizontal shells
    • Solid layers: Top 5 - Bottom 5
  • Infill
    • Fill density: 5%

(16) Add the main part from the 3D model.


  • Load Part - select the three slip parts

(18) Now you have all the parts and the main bodies, choose one part and click in the green cross.

  • Green cross
    • infill -> Fill density

(19) Change the Fill density to the desired one, in this case it will be 30%.

Repeat (18)(19) for the other parts.

(20) If you change to the Preview you can now see the variation of the infill, as we desired.

Step 5: Slicing - Simplify3D


(21) Import the 3 split parts and the main bodies at the same time.

(22) Select the four parts - let's align them, group and put them on the bed on the best position to be 3D printed

  • Edit
    • Align Select Models Origin
    • Group Selection
    • Place Surface on Bed - choose the surface in the model that will be in contact with the bed.
  • Center and Arrange

In S3r we select the part and then choose the settings to change, in this case it was the fill density. In S3D it's a little bit different, we need to create Processes and then apply them to the desired parts, so let's create the Processes.

(23) Create the Processes

  • Processes
    • Add
    • Select Models - choose the main part

(24)FFF Settings - Insert the main settings as the S3r, and change the fill density, named in S3D with Interior Fill Percentage.

  • Infill
    • Interior Fill Percentage: 5%

Repeat (23)(24), for the other parts, in (23) you could select the 3 split parts at the same time for only one Process. With the two Processes now we can generate de toolpath.

(25) Generate de toolpath

  • Prepare to Print!
    • Process Selection - choose the 2 processes
  • Printing Mode
    • Continuous printing: layer-by-layer

(26) Preview Mode and save the toolpath as a g-code

Step 6: 3D Printing

As mentioned before, the 3D printer used was a BEETHEFIRST by BEEVERYCREATIVE. In this step, I will show some photos of the printing process, and the final 3D prints.

The 3D parts were 3D printed without the tops and bottoms for a better visualization of the different infill densities.

(27)(28) 3D Printing process.

(29) Final 3D parts - Slic3r vs Simplify3D.

(30)(31) S3r 3D print details.

(32)(33) S3D 3D print details.

The final S3D print was a little bit different from the S3r. As we can see in (32)(33), S3D generates perimeters for each split part of the model. This could be better internally by giving a strong area of bond between fill densities, but externally the finish of the entire 3D model is compromised.

The ideal solution will be the exterior result of the S3r and the interior of S3D (maybe the issue of S3D could be resolved).

Step 7: Result

The purpose of this project, besides the demonstration of the advanced functionality in S3r and S3D, was to develop a 3D model that would be used with the 750 gr filament spools.

(34)(35) The default filament spool (330 gr) that comes with the BEETHEFIRST was placed inside the 3D printer, but due to the size (exterior diameter) of the 750 gr spool, we cannot put this spool in the same place of the 330 gr filament spool.

(36)(37)(38) The solution was to keep the spool's default location, in order to not decharacterize the BEETHEFIRST. In the end I think the goal was achieved.

Step 8: Final Considerations

In this instructables I aim to demonstrate, in a simple way, how to reinforce a specific region in a 3D printer part, by changing the part's infill density. By doing so, we avoid the necessity of big densities of infill in the entire model, and so we can reduce the filament used and speed up the 3D print.

P.S.: I'm not a Fusion 360 simulation expert (I saw some tutorials in the YouTube Autodesk Fusion 360 channel), but for simple and individual parts it's easier do this type of static stress simulation. And I started to use Simplify3D just a few days ago, so maybe the issue with the perimeters of the 3D model's split parts could be solved.

Enjoy!. ;)

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    3 years ago

    Excellent tutorial, I fought modifying infill inside a model was a feature found only in slicers like simplify3D. Thanks a lot