I am a beginner. I want to export a blender object to be cut on a CNC machine, the workshop ask me for a .stp file or a .igs file. My blender object has 250,000 tris, when I export to .stl the file size is 9mb but if I convert this file to .stp it becomes a huge 500mb file. Is there anything I can do within Blender before exporting the object to make this file size more reasonable?
This is a good question, and the answer unfortunately is mostly "no". IGES and STEP files are (mostly) CAD/CAM files, and are not point- or polygonal-based. The file format itself is ASCII, and dates back into the 70s. It is great for driving CNC machines, since that's its history.
Some modeling programs (Rhino) can get you there from nurbs-based modeling. I am not aware of any option in Blender (or ZBrush, Maya) allowing you to get a clean IGES. You can get STL files, which are great for 3D printing and which some routers will accept.
There are a number of programs that will go back and forth between Nurbs, STEP and IGES... and some higher-end products (SolidWorks) will bring in an stl and generate an IGES or STEP.
If you finda better answer -- post here. We use Blender for a lot of 3D output, but when we need tooling, typically we need to have IGES... and this is the best info I have at the moment!
You could also potentially just convert your model to STL and then have your part 3D printed in PLA. There are some good videoes on youtube of people using 3D printed PLA parts over wax for casting. Check on 3D hubs for an affordable printer near your location. Also check out fusion 360. It is a free CAD program. You can export from blender to obj, and then import into fusion and convert the mesh into a BREP which you can export to step. Converting from mesh to BRep can be tricky if you don't have a clean mesh. You may need to use netfabb or meshlab to repair it.