FreeCAD: Involute Gears

[last updated: 2020-06-08]
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jump to: add gear to spline
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• The tool to draw involute gears is in the Part Design workbench.
• Fumbling through the learning curve. No clue what I'm doing. Some of what's below doesn't work all the time ...
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• Create a free-floating gear:
• Open a new drawing
  Select Part Design workbench
  Create a new Body
  Under Part Design tab, select Involute Gear
  On my system this is confusing, because there is a line ("Involute gear...") in the drop-down that is (sometimes) greyed-out ie. inactive. Below that however, is a line ("Migrate"), and below that is a line ("Involute gear...") that is indeed active and is the command I've executed for all these procedures.

  Enter number of teeth desired,
  Enter module desired (this is approx. 1/2 the width of a gear tooth at its base):

  • The size of the teeth determines the resulting OD for a given number of teeth.
  • eg. for a 10-tooth gear:
    module = 0.8 gives a gear OD = 9.56mm
    module = 2.5 gives a gear OD = 29.9mm
  • In order to mesh, two gears must have the same module.

  Enter Pressure Angle desired:
        This determines the shape of the teeth
  Apply, OK

• Select 'InvoluteGear' in the model tree
  Click Pad icon, enter desired dimension, OK
• This creates a gear.

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• Add a gear to a cylinder:
  (This works, however in the end, unless there's some need to do it this way, it's easier to do it the other way around, ie. add the cylinder to a gear that you've drawn with above procedure).
• Open a new drawing
  Select Part Design workbench
  Create a new Body
• Create a cylinder:
  • Create a new sketch
    Select XY plane, OK
  • Select create circle icon
    Select origin, drag, click to place, escape to clear selection
    Click perimeter, click constrain radius icon, enter desired value, OK
    Close sketch edit
  • With Sketch selected in model tree, click Pad icon, enter desired dimension (suppose 5mm), OK
    A cylinder will be created
  • In model tree, 'Sketch' will change to 'Pad'. hover over 'Pad', right-click, select Rename, and rename 'Pad' to 'cylinder'
• Create the gear:
• Make sure Body is active (double-click Body in model tree if necessary)
  Part Design tab, select Involute Gear (see note [to be] elsewhere about which line in menu to select...)
  Enter eg. 10 teeth and Module 1.5mm (or whatever parameters desired), Apply, OK
  InvoluteGear will be created in drawing, centered at the origin
  New line 'InvoluteGear' will be created in the model tree
• Select 'InvoluteGear' in model tree, click Pad icon, select thickness dimension, click OK
  'InvoluteGear' will be changed to 'Pad001'. Rename it to 'gearDummy'
  The gear will be created superimposed, ie. in the same space, as the cylinder
  If the gear thickness is greater than the cylinder thickness, the gear will protrude out the "top" of the cylinder. Therefore, make the gear thinner than the cylinder.
• Click in drawing in center of gear space. It will highlight.
  Click Pad icon, enter dimensions, click OK
  A gear will be created, protruding out the face of the "bottom" of the cylinder
  Rename 'Pad00x' to 'gear'

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• Adding gear onto spline drawing:
  No clue why I have to do it this way, but this is what worked...
• Open spline template (.../25-t spline 4.8-6.7 + gearBase/splineTemplate-01_DO-NOT-EDIT.FCStd)
  Save-as to a new name.
  Select Part Design workbench.
  The spline in this drawing is not yet extruded.
  If necessary, edit Sketch002 (under splineHub) for optimum ID/OD of spline
  (currently 4.8 / 6.7 = 2.4 / 3.35 rad)
• Select gearBase in model tree (? not necessary ?)
  Select bottom face of gearBase cylinder in drawing
  Part Design tab, InvoluteGear
  (make sure it's co-planar with the bottom face of the gearBase)
  Enter 10 teeth, modulus 1.5mm, Pressure Angle 20deg
  Apply, OK
• Select InvoluteGear in model tree
  Drag it into Body (copy icon shows in cursor)
  InvoluteGear listing in model tree will now be indented
• Select InvoluteGear in model tree
  (... and this is the weirdness I had to do ...)
  Select Pad (or Pocket) icon, 1mm thickness (anything less than thickness of gearBase)
  Involute gear will change to Pad00x (or Pocket00x)
  Hover, right-click, rename to "gearTemp"
• Select gearTemp in model tree (actually doesn't seem to be necessary...)
  Click in drawing in center of gear
  Click Pad icon, enter desired thickness, click OK
  Hover, right-click, rename to "gear"
• Gear will be created on top of gearBase cylinder
• Select sketch002 in model tree (spline sketch)
  click Pocket icon, select desired depth (5mm?), click OK
  hover over Pocket in model tree, right-click, rename to "spline"

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