How to Modify Imported Parts (*.stl?)

aaron_szumilak

I've commissioned a professional engineer to design some very complicated parts for me and I'd like import them into onshape with the desire to change some dimensions of the parts as needed. Basically my project is going to be trial and error, so I'd like to be able to modify some of the parts provided so that I can 3D print a series of them. Each with slightly different dimensions.
However when I import the *.stl file I've received, it shows up as a complete part (as a series of meshes actually) and I cannot seem to change any dimensions of the imported part.
What file format should I ask my engineer to provide all of the parts in so that I have the ability to modify them as needed in onshape. 
He's using a very specific CAD modelling package called propCAD, however it can export the files as almost anything. dxf, stl, pro eng, igs. 

brucebartlett

I'd ask for a STEP file. Then use the direct modelling tools to edit the shape.

philip_thomas

STL is the CAD equivalent of a pdf, you can print it but you cannot modify it. As Bruce stated, you want a B-rep (boundary representation) model (Parasolid or STEP).