Catia Users

I downloaded a chassis file from online and tried adding to it.

I tried saving the chassis as a part and starting an assembly using it, that didn't work. The part only saved as the base plate of the chassis and not the entire chassis.

Then I tried just editing the chassis in it's file. The issue with that became the chassis seems to be mirroring everything over the z axis. Is there any way to turn off this continuous mirroring? Or any suggestions as to making it work?