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. Both live on the toolbar's Reference chip: the Axis menu holds four tools, the Point menu five. X is the shortcut for Axis through 2 points, D for Point at a face centre.
Neither draws material. Both are anchors: geometry you make on purpose so the rest of the model has something dependable to hang off.
Axes
| Tool | What it asks for |
|---|---|
| Axis through 2 points | Two vertices or reference points |
| Axis of a cylinder | One cylindrical face |
| Axis where two planes meet | Two planes: model faces, reference planes or world base planes, in any mixture |
| Axis normal to a face | One plane, and a point for it to run through |
Axis through 2 points needs them to be distinct: two picks on the same vertex leave nothing to aim along, and you get Selected points must be distinct.
Axis where two planes meet takes two flat faces of the part just as happily as two reference planes — you no longer have to build a datum on each face first. The one arrangement it cannot use is two parallel planes, which have no line to find: Selected planes are parallel — no intersection axis exists.
Points
| Tool | What it asks for |
|---|---|
| Point at a face centre | One flat face |
| Point at a circle centre | One circular edge |
| Point at a cylinder centre | One cylindrical face |
| Point at an edge midpoint | One edge |
| Point where an axis meets a plane | One axis and one plane |
A round edge means two different things, and only you know which. Point at an edge midpoint lands on the rim; Point at a circle centre lands in the middle, which is what a peg wants to mate to. They are two entries on the same menu precisely because no selection can tell them apart — so the menu asks instead of guessing, and the edge you already clicked is carried straight into whichever one you choose.
Point where an axis meets a plane fails when the axis runs parallel to the plane, which is the one case where they never meet: Axis is parallel to the plane — they do not intersect.
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 Point at a 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, and V does the same from the keyboard with exactly one reference selected — the same key that hides a body. Off means 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.
The References window lists all of them beside the planes, with an eye on every row, and a colour swatch: axes are magenta by default and points amber, and you can give any one of them a colour of its own so two are never mistaken for each other.
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