OneTaskBy Tim King · Updated
OBJ to STL
Binary or ASCII STL With Up-Axis and Millimetre Scaling for Your Slicer
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How the OBJ To STL works
This OBJ to STL converter prepares a modelling file for 3D printing. Drop a Wavefront .obj, check its orientation in the viewport, scale it to millimetres if it was modelled in metres, centimetres or inches, and download a binary or ASCII .stl that any slicer will open. The model stays in your browser; nothing is uploaded.
OBJ to STL: from modelling to printing
OBJ is the common export from modelling and sculpting programs, and many model libraries offer it as the default download. Slicers such as Cura, PrusaSlicer and Bambu Studio prefer STL. The converter reads every object and group in the OBJ, bakes their transforms, merges them into one body and writes the triangles. Quads and larger polygons are split into triangles on the way, and materials and textures are dropped because STL cannot hold them.
Getting the size right
STL has no units, and slicers assume millimetres. An OBJ made in a program set to metres arrives 1,000 times too small, often as a speck on the build plate. Choose m to mm, cm to mm or inches to mm to scale the model on export. The size stat in the rail shows the source dimensions, so a figure about 0.2 tall is almost certainly in metres.
Up axis
Most OBJ files are Y up, while printers build along Z. The default turns a Y up model so it stands on the build plate. If the preview shows it lying down, the OBJ was saved Z up; switch the menu so the rotation is skipped.
Binary or ASCII
Binary STL is compact and read by every slicer, so it is the right choice nearly every time. ASCII STL is a text file several times larger, useful only for old tools or for reading the triangles by eye.
FAQ
Why is my model tiny in the slicer?
The OBJ was modelled in metres or centimetres, and the slicer reads the numbers as millimetres. Convert again with m to mm or cm to mm, or scale it in the slicer by 1,000 or 10.
Does the converter repair the mesh?
No. Holes, flipped faces and zero-thickness surfaces carry straight through. Check the result with the STL dimensions checker, which reports open edges, and fix problems in a modelling program before printing.
Are separate objects kept apart?
No. STL has no parts, so everything in the OBJ becomes one body. Objects that overlap will be printed as one piece; objects that sit apart can still be separated with your slicer's split to objects command.
See also: all Images tools, Units, Audio & Video, Documents, Data & Code.
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