I often need to open a STEP file just to check a few dimensions, and the usual options are either a full CAD package that takes ages to start, or a free viewer that struggles with big assemblies and can barely measure. So I built Dioptra, a small Windows viewer that runs from a folder, no install. - Opens big STEP assemblies fast: large files are split across several OpenCascade kernels in parallel (a 171 MB, 3,092-part assembly opens fine), and a file you've opened once reopens much faster - Measurements come from the exact B-rep geometry: diameters, distances, angles, face-to-face, edge lengths, pinned in the view - Cut planes with filled sections, glass view, and a wall-thickness map - Solo any sub-assembly from the outliner; STEP colours kept - An exploded view that works out how parts come off (screws head first, bolt circles fan out) - Meshes too (STL, OBJ, FBX): flat faces are recognised when their triangles line up, and holes and round faces are fitted as true circles and cylinders, so you can measure a mesh almost like CAD. If a round shape isn't picked up, you can force it in one click. Full disclosure: it's my own project and it's paid (14-day free trial, then a one-time licence). Link in the comments. I'd love feedback from people who open STEP files all day, especially files that open slowly or measure wrong.   submitted by   /u/Grobenn   to   r/cad [link]   [comments]