Centerlines and construction geometry in SolidWorks

In AutoCAD there was such a thing as a Construction Line. In a sketch that is in a SolidWorks part file, a sketch entity (lines and circles are the most common ones) with a centerline linetype are always considered construction geometry. So you may see or hear some reference to a centerline as a construction line, or as construction geometry.

From the SolidWorks help file:
“You can convert sketch entities in a sketch or drawing to construction geometry. Construction geometry is used only to assist in creating the sketch entities and geometry that are ultimately incorporated into the part. Construction geometry is ignored when the sketch is used to create a feature. Construction geometry uses the same line style as centerlines.”

When you want a new construction line to use as construction geometry, it can be drawn as a construction line right off the bat because there is a separate command for a construction line. That command is simply called Centerline.

When you want a new piece of construction geometry that is a circle (this is not nearly as common as wanting a new construction line), this is not quite as simple as drawing a new construction line because there is no separate command for drawing a construction circle as there is for drawing a construction line. The new circle needs to be drawn on the screen first and then there is a check box in the property manager to change the circle to construction geometry.

If you have regular lines or circles (or other sketch entities) that you wish to turn into construction geometry, you can select the entity with a normal left click (or select multiple entities by holding the Shift or Ctrl keys as you select) and then on the shortcut menu that pops up you can select the icon to change to construction geometry. But it is quicker in the case of lines and circles to just draw this geometry right off the bat as construction geometry.

• It is common to draw straight construction lines right off the bat as opposed to drawing a line first and then checking the “For construction” option in the property manager.
• It is common to be working in a new sketch and convert entities from another sketch into the current sketch. (This produces an on-edge relation.) These newly converted entities could be “regular” geometry or if you wish they could also be converted into construction geometry.
• It is common to be working in a new sketch and convert an edge or edges from a solid body edge (including tangent edges in the case of dimensioning a form punch for example) into the current sketch. (This also produces an on-edge relation.)