FreeCAD-studygroup-session2

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Prerequisites

PLEASE NOTE: If you missed the January 17th study group session you will need to complete the prerequisites listed on this page ON YOUR OWN and PRIOR to coming to this session. We will not be covering those topics again and those found to not have these prerequisites completed will be asked to drop from this session.

In addition to either attending the First Session or alternately completing the youtube links from that page, you will need the completed model from our first session. You can obtain a copy from the below link. Please note, you will need to click the download link at the top of the page as this link will display the contents of the fcstd file when clicked on:
freecad-studygroup-session1.fcstd

Below is an Overview of the topics planned to be covered on January 31, 2015:

Continuation of sketching and pocketing on the existing model.  See above if you need the file

  • Go into Part Design
  • Choose menu item: Part Design/Create sketch.  Look at your model and choose the axis onto which to draw design.  Design should be on an axis where a face does not already have a pocket on it
    • Note: Your box may block your ability to see your sketch, go back to model and use space bar to hide the box so you can work with sketch.
  • Create arc anywhere in the upper right quadrant of intersection of the axis
  • Constrain center point of arc horizontally 37.5 and vertically 38 from the intersection of the axis (0,0)
  • Create second arc anywhere in the upper right quadrant of the intersection of the axis, but inside the previous arc
  • Constrain center point of new arc horizontally 25.5 and vertically 33.5 from the intersection of the axis (0,0)
  • Coincident constrain the top two points of the arcs together and then the bottom two points of the arcs.
  • Create a line and coincident constrain the line ends to the two points of the arcs
  • Constrain length of line to 45
  • Drag around so that line angles upper left to lower right and generally fits a nice looking moon inside the box face
  • Constrain bottom point of line horizontally 25 from the intersection of the axis (0,0)
  • Moon should now go green and be fully constrained
  • Toggle line that connects the arc points to be a construction line
  • Close sketch
  • Unhide box if you hid previously
  • Click on one of the faces without a pocket and click Part Design/Map Sketch to face.  Select moon sketch.  Click OK and Close.
  • Pocket through all

Choosing an external line from 3d model to constrain

  • Create new model
  • Create new L-shaped part
    • Go to part design workbench
    • Create new sketch on XZ plane
    • Draw rough L shape around the intersection of the verticies
    • Vertically constrain 3 roughly vertical lines and horizontally constrain 3 roughly horizontal lines
    • Select top two points of top horizontal line and then Z axis (in that order) then constrain equidistant (symbol looks like ><)
    • Select right two points of right vertical line then X axis (in that order) then constrain equidistant (symbol looks like ><)
    • Make top horizontal line 20 in length
    • Make left vertical line 40 in length
    • Make right vertical line 20 in length
    • Make bottom horizontal line 50 in length
    • Sketch should go green and you should be fully constrained now.  Click close.
    • In Model click sketch and choose Task tab
    • Pad sketch to dimension 80 and Click OK – you should now have an L bracket
  • Pocket two screw holes on new L-shaped bracket using external line
    • Click on the lower (wider) inside face of the L and choose Part Design/Create Sketch
    • Create two circles with 7 radius (you can set one to 7 and equality constrain them both)
    • You need to measure from the inside angle of the L – click the icon that looks like a box with a dotted line above it.  When moused over it says “Create an Edge Linked to an External Geometry” then click on the line in the middle of the view.  It should turn green and either end of the line should now have an end point you can map to.
    • Constrain middle of top circle 18.25 vertically from top point of external line
    • Constrain middle of top circle 15 horizontally from top point of external line
    • Constrain middle of bottom circle 18.25 vertically from lower point of external line
    • Constrain middle of bottom circle 15 horizontally from bottom point of external line
    • You should now be fully constrained.  Close and pocket through all.
    • Show how you can’t change radius of holes in pocket, but changing constraints will effect 3dmodel by moving  the circles to 22 vertically from either end.

Fillets & chamfers.  Scenario: the outer edge of the L bracket doesn’t slide nicely into a corner:

  • Select the line of the outer edge by clicking on it.
  • Choose the Fillet icon and put in 20, click OK.  Note how the line gets nicely rounded
  • Undo by selecting the fillet from the combo view and deleting it.
  • Select the same line and this time choose Chamfer and put in 10, click OK.  Note how it angle the object.

Exporting to STLs

  • In order to print on a 3d printer, you’ll need to translate the model from the native FreeCAD format to something understood more universally, in this case, STereoLithographic format or STL.  You can export from FreeCAD by selecting items that are bold in the combo view with ctrl-click and then choose File/Export.
  • Drop down and look for “Mesh Formats” and put in a name.  You can specify the stl extension but FreeCAD will presume STL if you don’t select it.
  • Save your work in native FreeCAD format as well
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