Cut with Voids When Loaded - 'Cuts Geometry' Postscript

Following my earlier blog post on Cut with Void When Loaded in Revit, I have discovered another subtle exception to the rule:

It does not work properly with the new Revit 2021 feature "Void Cuts in Family Geometry" that allows you to turn the 'cutting capability' voids on/off in a family.  NB. This is sometimes referred to as turning off Void visibility, which is misleading.

Void in Family Editor

Here is a workflow that demonstrates the confusing behaviour:

• In the family editor, create a new Generic Model family
• Tick the 'Cuts with Void When loaded' family property

• Create a solid with two more intersecting solids
• Change the two outside solids to voids 
• The voids will not cut the solid - this is a deliberate technique to carefully control what cuts what
  

• Use the 'Cut' command to cut one of the voids from the solid (only one)

• Select the visible void and link its 'Cut Geometry' property to a parameter - say "Cut Rect"
  

• Select the invisible void (that is cutting the solid)
• link its 'Cut Geometry' property to another parameter - say "Cut Cylinder"
  

• In theory, this should allow you to turn off 'cutting capability' of each void independently, once in the project - and hence whether they cut or not.

Test this in the Family Editor

• With both voids 'cuttable', the cylinder cuts but the rectangular void does not (as expected) - this is because the rectangular void was never told to cut the solid, so it has no effect in the family
  

• Turn off the 'cutting capability' of the cylinder - it no longer cuts the solid;  it actually becomes visible, which may seem contradictory - but that is typical Revit behaviour (voids not cutting anything show orange;  voids already cutting a solid disappear)
  

Switch the cutting properties around so the cylinder can cut but the rectangular cannot - visually it looks the same as having both properties ticked.

 Voids in the Project

From my earlier blog post on Cut with Void When Loaded in Revit, we know that in order for it to work in a project, the cutting void must be set to not actually cut anything in the family - as the rectangular void is set up.

 

• Load the family into a project

• Place the family onto an element that it intersect with
• Both 'Cut Geometry' checkboxes ticked
  

• Untick both checkboxes, so the cylinder void is no longer cutting the family solid (rectangular void does not cut it regardless)
• Both voids are ghosted when the family is selected, or in pre-selection
  

• Use the project 'Cut geometry' command with the host element and family

• Both voids will cut the host element (neither void is cutting the family solid)
  

• Tick the 'Cut Rect' checkbox -
• The cylinder is not cutting the family solid, so it cuts the host element in the project (this may not be what you want, but it cannot be avoided!)
• the rectangular void is not cutting the family void, so it cuts the host
  

• Tick both boxes - only the rectangular void cuts the host (as it is not cutting the family solid)
• The cylinder now cuts the family solid but not the host (and is no longer visibly ghosted)
  

Conclusion

• If the void cuts a solid in the family, it cannot cut an element in the project using the 'Cuts with Void When loaded' family property
• If the void cuts a solid in the family,the new (in v2021) 'Cut Geometry' property has the potential to work in a project
• If the void does not cut a solid in the family, it can cut an element in the project using the 'Cuts with Void When loaded' family property - but only when you use the 'Cut' command in the project
  
• If the void does not cut a solid in the family,the new (in v2021) 'Cut Geometry' property has absolutely no effect in the project

This probably makes sense if you think really hard about decisions the programmers had to make about what is possible and how it might work.

However, it is mighty confusing for the end user.

To make matters worse, we now have two entirely different 'Cut Geometry' functions in Revit:

• 'Cut Geometry' property in the family - a checkbox
• 'Cut Geometry' command:
• in the family- where you actively select which elements cut each other
• in the project - where you actively select which family cuts which element but the results depend on all kinds of things in the family (as described above).

All clear now?  Or still confused?

Cut with Voids when Loaded in Revit

When this new feature appeared in Revit about 10 years ago (v2012?), it was always a bit mysterious - it had many confusing restrictions about how and when you could use it

So, what is this family property that shows up in the Family Editor in Revit?

Autodesk Help in v2021:

Autodesk Help

"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),
• Ceilings, 
• Floors, 
• Furniture (not listed in the help file or tooltip),
  
• Generic models, 
• Roofs,
• Specialty Equipment (not listed in the help file or tooltip),
  
• Structural columns, 
• Structural foundations, 
• Structural framing,
• Walls

• 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.