Union Command

[1964joe]

Can anyone tell me why I would not be able to use the UNION command to join some 3D Solids? I am working in a large 3D model and I'm trying to create some new sub-objects that are 3D solids. When doing so, I am usually able to UNION a bunch of 3D solids to create one, but in some instances it doesn''t work. I get no prompt for the reason why - the command line looks as though the command finished properly, but it doesn't work at all.

[bcgatti]

I don' t know if this fits your problem or not, but I have found that sometimes if the resulting solid is too complex for AutoCAD to calculate that it doesn't complete a Union or a Subtract.

[jaberwok]

Changing the order in which you select the objects can make a difference.
Also, if you are selecting several objects at once, try selecting only two at a time - reduces the calculation complexity.

[1964joe]

I am relatively new to 3D AutoCAD, but I think I've solved the problem. I am creating a solid model of a hotel and I think that the 2D drawings that I'm using to create the model were exported from Revit. Somehow the exported drawings are not 100% accurate.

For example, where 3 lines meet to form one intersection sometimes do not. The endpoints of the line may be a little different (miniscule differences - <.001"). That creates a gap between the solids, so when I try to UNION them it doesn't work.

I despise inaccurate drawings. . . .

[jaberwok]

If you need the effect of stretching an object, make a copy of it slightly displaced (.001" in your example), union Last and Previous, then do the union that you wanted.