Reference Axes and Points
Use a reference axis to give a revolve, a sweep or a pattern a line to work around. Use a reference point to name a spot the model does not have a vertex at. Select what each is built from, then press X for an axis or D for a point.
Neither draws material. Both are anchors: geometry you make on purpose so the rest of the model has something dependable to hang off.
Axes
| Kind | Select first |
|---|---|
| Two points | Two vertices or reference points |
| Cylinder axis | One cylindrical face |
| Normal to face | One face and one point |
| Plane intersection | Two reference planes |
Two points needs them to be distinct: two picks on the same vertex leave nothing to aim along.
Plane intersection wants two reference planes, not two faces of the model.
Points
| Kind | Select first |
|---|---|
| Face centre | One face |
| Edge midpoint | One edge |
| Axis ∩ plane | One axis and one plane |
| Circle centre | — |
| Cylinder centre | — |
The first three come straight from a selection. Circle centre and cylinder centre do not: pick an edge and you get its midpoint, pick a face and you get its centre. To reach either, make any point, then change the Variant row at the top of its panel and pick again.
Axis ∩ plane fails when the axis runs parallel to the plane, which is the one case where they never meet.
Why you would bother
A reference point is the way to give a step a spot that is not a vertex. The Point to point step in a Transform accepts vertices and reference points and nothing else, so a hole centre is out of reach until you make a reference point at it. Use Circle centre on the hole's edge, and the step can then mate a peg into it.
An axis is the same story for anything that turns. A revolve, a helical sweep, a circular pattern and a clearance cut all want a line, and a reference axis is a line that survives edits which would move a model edge.
Hiding them
Both have a Visible switch in their panel. Turn it off and the axis or point stops being drawn, and stops being clickable, while everything built on it keeps working. Turn it back on to pick it again.
See also
- Reference Planes: the third kind, and the one you will make most
- Using References: what they feed, and what breaks when you delete one
- Working with Several Bodies: mating parts is where most axes end up