Part Modeling > Engineering Features > Hole > Hole Placement References
  
Hole Placement References
You can place a hole in a model by selecting different placement reference combinations:
A placement reference to position the hole, and offset references to constrain the hole position in relation to the selected references.
Two placement references, a datum axis and a surface. The axis does not have to be perpendicular to the surface.
1. Datum axis
2. Surface
Two placement references, a datum point and a surface. The point does not have to be on the surface.
1. Datum point
2. Surface
You can verify and modify the hole placement references at any time as you create your hole.
Placement Reference
The placement reference enables you to position the hole on the model. You can relocate the hole by dragging the placement handle on the hole preview geometry, or by snapping the handle to a reference. You can also click the handle and then select the primary placement reference. The hole preview geometry relocates.
Offset References
Offset references enable you to use additional references to constrain the hole position in relation to selected edges, datum planes, axes, points, or surfaces. You can define the offset references by snapping the secondary placement handles to references. The secondary (offset) reference value appears in the graphics window as shown below:
 
You cannot select an edge that is normal to the placement reference.
Although offset references are needed for coaxial holes, placement handles are not available. Activate the offset reference collector and select the references.
You cannot select an edge to define an internal datum plane. You need to create a new datum plane. You can do this within the Hole tool by clicking Hole > Datum > Plane. The Hole tool pauses and the Datum Plane tool opens.
Selecting the Axis of a Hole as Secondary Reference
You can select the axis of a hole or a datum axis as the offset reference. The selected axis should be normal to the placement reference of the newly created hole. You can also orient the orthogonal offset dimensions to be parallel to the specified direction by selecting an orientation reference.
The offset dimensions are oriented in such a way that the first offset dimension is parallel to the orientation reference as shown in the following illustration. However, the first offset dimension is no longer parallel to the offset dimension of the axis of the hole used as the offset reference.
1. Orientation reference
2. First offset dimension parallel to orientation reference
3. Newly created hole
 
If you select a datum axis created with two offset references or the axis of a linear hole as the offset reference, then a default dimension orientation reference is assigned and the hole is fully constrained.
If you select a datum axis created without any offset references or the axis of a hole other than a linear hole, then you must specify a dimension orientation reference.
Verifying and Modifying Hole Placement References
You can verify your placement references using the preview geometry in the graphics window or by using the Placement tab. This tab contains the primary and secondary reference information. You can also change the placement type in the placement Type box.
While the Hole tool is open, you can select new placement references or modify the offset placement reference values.
 
* If the primary placement reference changes, the existing secondary references are used only if they are valid for the new hole placement.