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Getting Rid of Excessive Materials from a Family
Before I get into the topic matter, let me clear up some issues concerning face based families. As you may know by now, I've contributed a few classic furniture at RevitCity. However, I forgot to mention that those families are face based families. I had assumed that users will quickly find that out after they load the families in a project. Apparently, a few users are not familiar with how face based families work, judging from a few comments I've read. I'll use the Mart Stam chair as an example:(
Here is is my reply to user luismendez (this is also applicable to the rest of the classic furniture I've uploaded at RevitCity):
The Mart Stam family is a face-based family that will attach to ANY surface. If you've loaded it to a project without a floor, the cursor will show a circle with a slash symbol and clicking will not place the family. If there is no floor or surface to attach to, it can still be placed by clicking the Place on Work Plane button from the Placement panel of the contextual tab. The family will then be placed at the default level which is Level 1. To pick a new host, simply click the Pick New button from the Work Plane panel of the contextual tab. You then have the option to either place it by Face or Work Plane by clicking the appropriate buttons from the Placement panel. In an existing project, face based families attaches to any surface (walls, floors, ceilings, soffits, etc. or even the top or side of an existing component).
Excessive Materials
I must apologize to RevitCity user pchan. In my haste to contribute this family to RevitCity, I simply forgot to purge the hundreds of materials that were on the MR Chaise lounge family:
Back in 2009, I was using a custom face based template that contained hundreds of materials. it was the template I used to experiment on complex family modeling.
Anyway, the good thing about this inadvertent mistake is the chance for me to explain how to get rid of excessive materials from a family. I know a lot of users have come across this dilemma. Well here's a fix for the MR Chaise family that shouldn't take more than five minutes (as opposed to deleting each material one at a time):
1. Open the MR Chaise family. Switch to the default 3D View. Select the MR Chaise family with the selection cursor (window selection method).
2. In the Create panel of the Modify | Multi-Select contextual tab, click the Create Group button. Type a name for the group. Keep this file open for the next step.
3. Open a new Generic Model face based template (Application>New>Family>Generic Model face based.rft). Save this file as MR Chaise_New (Application>Save As). Leave the view as is (Ref. Level view).
4. Switch to the MR Chaise family window (click the Switch Windows icon from the QAT). Select the group and click the Copy to Clipboard button from the Clipboard panel (or press Ctrl + C).
5. Switch to the MR Chaise_New window. Click the Paste drop-down button from the clipboard panel and select Aligned to Current view. The Properties palette shows the Origin Level as -0' 0 77/128". Change this to zero.
6. Switch to the default 3D view. Select the pasted group and click the Ungroup button from the Group panel. The family is now free from all those excessive materials from the Mr Chaise family. The material parameter is also transferred.
7. However, when families with voids are copied and pasted to another template, the voids become unjoined (see fig. 1).

Figure 1
In this family, voids were used to smooth the edges of the cushion's edges. There are fifteen voids on each side. Select the Cut geometry tool (Modify>Geometry). Click a void then click the leather cushion. Do this for the rest of the voids.
That's it! To those who downloaded this family, I apologize for the inconvenience.