Defining a use case (surface selection)

A use case is a group of anchor and load surfaces.

A use case should be thought of as how the part will be constrained and loaded when put into service in a real-world scenario. Anchor surfaces are where the part is constrained from moving and load surfaces are where loads are applied to the part. 

Tip: Not sure what a button does? Hover over the button and a tooltip will appear.

Contents

Defining anchor surfaces

Anchor surfaces are surfaces that are fixed and cannot move. The anchor surface selection tool is shown below. Important features are:

  • To add another anchor surface, click the "Add" button. 
  • To remove an anchor surface, click the delete icon ("") next to the anchor.
  • Type is currently set to Fixed. This means the surface is fixed and is not allowed to move in any direction.
  • There are 3 Selection options. The left-most is for flat surfaces, the middle is for concave surfaces, and the right-most is for convex surfaces. 
  • To apply an anchor to a curved surface that is not cylindrical, select Custom. Click here for a description of the Custom surface selection tool.

use_case_anchor_21p0

Defining load surfaces

Load surfaces are surfaces where forces are applied to the part. The load surface selection tool is shown below. Important features are:

  • To add another load surface, click the "Add" button. 
  • To remove a load surface, click the delete icon ("") next to the load.
  • Type is currently set to Push / Pull. This means the load is either pushing or pulling on the surface. 
  • There are 3 Selection options. The left-most is for flat surfaces, the middle is for concave surfaces, and the right-most is for convex surfaces. 
  • There are 3 Direction options: Perpendicular (normal) to the surface, parallel to the surface, and the option to switch the direction of the load. 
  • The load Magnitude has units of Newtons (N). Enter a specific magnitude or adjust the magnitude using the slider. The load is evenly distributed among the selected surface.
  • A load arrow manipulator wheel appears for certain combinations of selection settings. To use the wheel, click and hold anywhere on the perimeter of the wheel and drag your mouse to orient the arrow.
  • To apply an load to a curved surface that is not cylindrical, select Custom. Click here for a description of the Custom surface selection tool.

Defining a load is simple. Just select a surface, define a load magnitude, and adjust the arrow so that it points in the intended direction. 

 use_case_load_21p0

An example of a load definition is shown below. The half-cylinder region of the lever is selected with Selection = Concave and Direction = Normal. The load magnitude = 200 N and the load arrow manipulator wheel has been adjusted so that the load arrow is orientated in the intended direction. Given these settings, the 200 N load will be evenly distributed across the surface in the direction of the arrow. 

use_case_loadExample_21p0

Custom curved surface selection

The standard surface selection tools are intended to be used on basic surfaces like planar or cylindrical surfaces. For surfaces with more complex curvature, or to select part of a cylindrical surface, we recommend using the Custom surface selection tool. To view the Custom selection tools, click the Custom button under Loads or Anchors. The Custom selection tools for loads are shown below.

  • The Selection Criteria are either Selection or Neighbors and these determine how angles are measured between facets (triangular surfaces) on the STL mesh. 
    • The Selection method will measure surface angles between the facet that you select and other facets in the STL mesh. This method usually selects fewer surfaces and allows for greater control.
    • The Neighbors method measures angles between neighboring facets, starting with the facet you initially select. This method usually selects more surfaces and allows for less control.
  • The Selection Angle defines the upper angle limit between facets. Smaller angles will typically select fewer facets compared to larger angles. 
  • For loads, the Load Direction is defined by manipulating 2 arrow manipulator wheels. The resulting unit load direction is shown in Cartesian coordinates and the values are relative to the coordinate system displayed in Cura. The Load Direction X, Y, and Z values are for display only and cannot be edited.
  • The load Magnitude has units of Newtons (N). Enter a specific magnitude or adjust the magnitude using the slider. The load is evenly distributed among the selected surface.

use_case_custom-1

Surface selection video

surface_selection_video

Selecting specific regions of a flat surface

In some situations, you may want to select a specific region of a surface instead of the entire surface. In such cases, there are some additional steps that that will allow you to select this "target" surface. These steps assume that a CAD representation of the part exists and you have access to a CAD software program.

  1. Open the part CAD file (STEP, IGES, native format, etc.) in your CAD program.
  2. Use the surface editing toolset to split/partition/divide the target surface from the larger surface.
  3. Use the extrude tools to push/pull the target surface. The depth of extrusion should be small - 0.5mm or less is recommended. The goal is to offset the target surface so that the SmartSlice surface selection algorithms can distinguish it from the larger surface while not extruding the surface so much that is affects the structural performance of the part.
  4. Export the part as an STL. Use a refined mesh instead of a coarse mesh if your CAD program has this option.
  5. Import the new STL into Cura, switch to the SmartSlice stage, and use the selection tools to select the new surface.

An example is shown below. With no partitioning, SmartSlice will select the full, flat surface as shown on the left. After following the steps listed above, a target surface was created and extruded. This new face can be selected in SmartSlice as shown on the right.

surface_offset

Notes:

  • A minimum of 1 anchor surface and 1 load surface must be defined to have a valid use case.
  • Cura uses STL files and as such, the SmartSlice surface selection tools have been designed to work with this file type. However, there are limitations inherent in STL files that make selecting certain types of surfaces challenging. This means that you may encounter scenarios where the surface selection tool is unable to select the surface you intended. We are always working to improve our selection tool and welcome your feedback.