In drawing your parts you will encounter challenges:

  • How can I make a Popsicle stick shape so the end arcs meet the straight lines perfectly?
  • How can I place mounting holes equidistant from each corner of a rectangle?
  • How can I place two holes evenly spaced between two other holes?
  • How can I move a circle so it’s tangent to two other circles?

Those new to CAD software often try painstakingly over and over to carefully position lines with the mouse, zooming in and out to check their results. And they use other ad-hoc methods such as nudging lines by very small steps to home in on a desired position. These methods get them close to the desired result but are not exact and are time consuming. 

There is a better way, one that’s fast and gives perfect results, called geometric construction. Geometric construction is a technique of combining commands to solve drawing problems. For example, to draw a Popsicle stick using geometric construction you might combine the rectangle, circle, snap and intersect commands to get a perfect result in seconds.

This page provides diagrams of many geometric construction examples. The diagrams assume you have learned how to draw, select, move, delete, stretch, rotate and snap basic lines. The techniques assume snap is on and grid is off.

Common Drawing Situations 

The techniques summarized below show several common situations encountered in drawings. For example, look at the “Draw a square” diagram to the right. Menu and keyboard commands are shown in blue. Changes are shown in red. 

Read it this way:

  • Hold down the Ctrl key on the keyboard.
  • Draw a diagonal line.
  • Draw a rectangle snapped to the diagonal line.

 Note: Correction for Polygon – Edit Preferences; 2D; Rotation Snap Angle; 360/5; OK; Edit Co/py; Edit Paste; Press R key; Edit Copy; Edit Paste; Moves lines into position.

Combining_Commands_1.gif (38684 bytes)

Positioning

The techniques below show a variety of methods of accurate positioning.     

Combining_Commands_2.gif (37906 bytes)

The videos below will show you several 2D tricks.

Position a Circle/Arc to create one shape:                                   Draw a circle/arc through points:                                   Move a circle to be tangent to another circle:

https://www.youtube.com/watch?v=5VBNxgI0BxU

https://www.youtube.com/watch?v=Tx8upmzdiU0

https://www.youtube.com/watch?v=VARLz86kZFU

Triangles

The techniques summarized in the drawing below relate to drawing situations involving triangles.Combining_Commands_3.gif (29540 bytes)

More 2D Shapes

To make a polygon with equal sides (e.g. equilateral triangle, pentagon, etc.):

  1. Draw a circle
  2. Select Line | Divide | enter 3 for a triangle, 5 for pentagon, etc.
  3. Draw straight lines between arc snap points.
  4. Delete the arcs.

To make an arced (banana shape) slot with round ends:

  1. Draw two concentric circles.
  2. Draw two straight lines from center at different angles thru both circles.
  3. Select all 4 lines and click Intersect.
  4. Delete extraneous line segments.
  5. Select the 4 lines of the slot and click Group.
  6. Click the round corner button and enter half of the width of the slot. 

https://www.youtube.com/watch?v=VEtNLxiCp0E

 

To make a spiral:

  1. Draw a 1″ circle.
  2. Click the Repeat button.
  3. Set the diameter to 1.1″
  4. Click the Repeat button.
  5. Set the diameter to 1.2″
  6. Continue as above up to the desired outer size.
  7. Move the 1.0″ circle away from the others.
  8. Snap the North snap point of the 1.1″ circle to the North snap point on the 1.0″ circle.
  9. Snap the East snap point of the 1.2″ circle to the East snap point on the 1.1″ circle.
  10. Snap the South snap point of the 1.3″ circle to the South snap point on the 1.2″ circle.
  11. Snap the West snap point of the 1.4″ circle to the West snap point on the 1.3″ circle.
  12. Repeat in the above pattern for the remaining circles. Be careful – one mistake can create trouble below.
  13. Select all.
  14. Intersect.
  15. File | Save
  16. Delete the line segments that are not part of the spiral.
  17. File | Save.

Note: This method is not technically a true mathematical spiral.

https://www.youtube.com/watch?v=uRcMgUyklhs