So, what is this family property that shows up in the Family Editor in Revit?
Autodesk Help in v2021:
"Cut with Voids When Loaded: When selected, voids created in the family will cut through solids. The following categories can be cut by voids: ceilings, floors, generic models, roofs, structural columns, structural foundations, structural framing, and walls."
That's it - all the help you will get from Autodesk on this one! It hardly explains much about how to use it. If you dig deep you might find more information - but there is no link to it.
It is inaccurate in that it says "voids . . . will cut through solids". It should say "may cut. . . "
It is also not up to date with its category list.
In Revit the tool-tip is pretty much the same, although it does at least have a diagram that shows why you might want to use it:
This is a classic example of inconsistency in help and tooltips. I remember during beta testing that we asked for the ability to cut holes in worktops using this new feature - worktops are usually in the "Casework" category, which was not included in the list of cuttable categories. Luckily it was added as a further enhancement a year or two later - but Casework does not appear in any lists from Autodesk, even though it was used in this illustration.
[Edit] If you dig deeper in the Autodesk Help files under 'Cut Geometry' , it does have an updated list of categories that can be cut by this method:
"You can cut objects in a project when a family with unattached voids is loaded.
Objects that can be cut include: Walls, Floors, Roofs, Ceilings, and Structural Framing, Structural Columns, Structural Foundations, Casework, Furniture, Specialty Equipment, and Generic Models."
I recently had a requirement to use this "new" feature in a Revit family - but I could not get it to work. So I decided to revisit exactly how to make it work:
How does it work?
- A void form has to be created in a Revit family
- Tick the "Cut with Voids When Loaded" checkbox in the family parameters
- The category of the family is not relevant to this feature
- Load the family into a project
- Place the family in the project in a location where the void intersects with an element in the model
- The element will not be automatically cut
- Use the "Cut Geometry" command
- Select the element to be cut, then the family with the void in it
- The element may or may not be cut, depending on the following rules:
Rules and Exceptions
- The element to be cut must be of one of the following categories:
- Casework (not listed in the help file or tooltip),
- Furniture (not listed in the help file or tooltip),
- Generic models,
- Specialty Equipment (not listed in the help file or tooltip),
- Structural columns,
- Structural foundations,
- Structural framing,
- The void in the family must not be cutting anything in the family - this is the rule that caught me out recently. To get around it I had to create two voids:
- The first one to cut elements in the family
- The second one to cut elements in the project
- [Edit]There are two ways to prevent the void from cutting elements in the family:
- 1. You have to create the void in a location where it does not intersect any geometry,
- then move it to the correct location - it will not cut any intersecting geometry;
- 2. Or create a solid where you want it, and change it to a void - it won't cut unless you tell it to [Thanks to Simon Weel for reminding me of this method]
- [Edit] I have had problems with saving families that only contain a void element that is not cutting anything - but I think that only happens for in-place families.
- Cutting only happens in a project
- This capability does not work in the family editor - when one (cutting) family is nested into another family. This is a very frustrating restriction - it means that you have to build additional voids into the parent family, which is a pain if you have complex angled geometry.
Once you understand those rules and limitations, you can use this capability to get families to selectively cut elements in a project. It does have some advantages over 'Face-Based' families that also allow you to cut into a host element:
- You can decide whether you want individual elements to be cut or not
- It does not need to be hosted - it can be placed directly in the model with its own parametric controls (height etc)
- It can be moved away from or to an element to be cut (it remembers the cutting status if moved away and back)
- This can be added to existing families (converting to face-based requires recreating families)
- The void can be anywhere in the family - it does not have to be related to a host face in the family (as face-based families do)
I hope this saves time for anyone who cannot get this feature to work properly.
In this example I have carefully made the void slightly bigger than the basin for clarity in the illustrations - and to make sure that water runs down the side of the basin into the casework and rots the timber. I suggest that you make it a closer fit or use lots of silicon to seal it.