Open a new sketch.
Our shape will be rotated by 14.24 deg. It is result of specified valves timing. Lets draw two connected lines: one horizontal, second rotated by 14.24 deg. Set second line length to 21.5. Next set they construction mode.
I need harmonic cam working with flat-faced follower. It can be constructed from four tangent arcs.
Take look at 21.5 mm line: left end will be bigger arc centre, right is for smaller arc centre. Draw arcs as in the above picture.
Now I should connect those arcs with two next, tangent arcs... but current (4928 SVN) FreCAD have not arc-arc tangency support. I drew two short, tangent for arcs, construction lines.
Next I connected arcs with second two (big radius ~100) ones. One of them I made tangent to two short construction lines. Additionally I set up first two arcs radius to 14 and 1.5 mm respectively. Connecting arcs should be exactly the same - use equality constraint for them and next set two points (one end of each one) symmetrical for 21.5 mm line.
Note: also radius of connecting arcs should be specified but I have problems with this in 4928 SVN FreeCAD. I'll return to this issue in the future...
Now you can make 12 mm pad. If shape isn't solid, check construction lines in the sketch.
Next I made second cam. This time shape is rotated by 167 deg from vertical line.
Now we have two cams: exhaust (first one) and inlet.
Select second cam and set Placement in Property view - Data. Set Z translation to -40.
For your convenience set names for Pads - click on it and press [F2]. Different colors also are useful - set they in Property view - View - Shape Color.
Now you can add next 6 cams: simply use Copy-Paste and Placement options.
| Cam | Z translation [mm] | Rotation around Z axis [deg] |
| Exhaust | 0 | 0 |
| Inlet | 40 | 0 |
| I | 88 | 90 |
| E | 128 | 90 |
| E | 176 | 270 |
| I | 216 | 270 |
| I | 264 | 180 |
| E | 304 | 180 |
And the final result:
Download model file.
FreeCAD 0.12 4928 SVN
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