Sometimes LEGO bricks don't fall into the regular 0.8/1.6mm rule. This will explain how to get "lumpy" 3D surface data from LDraw DAT files and use them to create your own intelligent parts.
*I use the AutoDesk Inventor Pro suite, which includes Inventor Pro and 3D Studio Max. I will discuss using certain file formats, but you need to determine what your software will import/export.
*I've been told that IV 2017+ will let you measure the LDraw data directly in Inventor, removing the whole 3DMax conversions steps.
Step 1: RESOURCES:
Your 3D modeling software.
LDView: http://ldview.sourceforge.net/ - You'll need this at the minimum.
LDraw (optional): http://www.ldraw.org/ - This includes LDView, but includes other programs which may be of interest. LeoCAD (included) will also allow you to accomplish what LDView does, with additional features.
LDraw Parts Tracker: TRACKER - this is where you download the DAT files.
Step 2: USAGE:
Ldraw parts contain a lot of information that you would not otherwise be able to obtain, even with measurement tools. However, some parts may be incomplete or missing features. Sometimes you can apply the 0.8mm rules or you can find an image of the real brick. Else, you have to make a "best guess" and just make the part "presentable". These parts import as "dumb" surfaces. The goal here is to get something you can measure and duplicate. Measurements are taken from the vertices.
Example: 2852 - Technic Engine Connecting Rod
(See images below)
1. Get the DAT from LDraw.org.
2. Open in LDView and export to STL. *STL will open in Inventor, but with no edges or vertices to pick from. YMMV.
3. Import the STL into 3DSMax and export to DXF. Now you have data you can measure. *In my case, I have to flip the X axis. IV and 3DS use different coordinate systems.
4. Import the DXF into Inventor. *You may have to adjust you import settings. I have to change my units to cm to scale correctly (among other settings).
My normal workflow is to place the part off-center in 3DS. When I import it into IV, the surface data will be off of origin a little. I now work in the same file, creating new IV data next to the imported model (see image 4). When completed, I delete the surface data, add iMates, refresh, purge, and save. Done
Step 3: CONCLUSION:
A lot of information can be gleaned from LDraw parts. Even if tagged as "unofficial" or "uncertified", most likely you will be able to open them and use the broken data. It's a lot easier and cheaper than Bricklinking the parts and measuring them.
Step 4: (Get the DAT from LDraw)
Step 5: (Open in LDView)
Step 6: (Import the STL)
Step 7: (Import the DXF)