STL Finishing

Round the edges of an STL file online

Downloaded an STL with sharp corners, a hole that scrapes, or edges that feel rough in the hand? Upload your model, choose a radius, and download a smoother, slicer-ready file. No CAD install, no mesh-to-solid conversion, and no rebuilding the model from scratch. Just butter-smooth edges.

Comfort Make a print feel smooth in the hand instead of sharp and blocky.
Fit Soften a rim or hole so the part glides into its slot instead of scraping.
Safety Take the sharp corners off before a print goes near hands, pockets, or kids.
Finish Give a downloaded model a clean round-over with no filing, sanding, or Dremel.
Rounded result Sharp input
Drag to compare. The same model with its rims filleted and its corners eased.
Round my STL edges → See how it works

Free to start. A couple of free roundings per day, topped back up daily. No sign-in required. Files auto-delete within 24 hours. Making a print from an image instead? Turn line art into a 3D bookmark →

Why is it so hard to fillet an STL?

STL files are triangle meshes, not native CAD solids. That is why a "quick fillet" on a downloaded model can turn into a long Fusion 360, Onshape, Blender, or FreeCAD detour: convert the mesh, repair what broke, remodel the part, and hope the export survives. If you just need to soften the edges before slicing, ButterySpace is built for exactly that one job.

And because the default Fillet mode rounds the rims in place, embossed lettering and recessed details on the faces survive untouched. The edges melt; the detail stays. The full story is in why STL files are so hard to edit.

How to round an STL with ButterySpace

  1. Upload your STL file (a download from MakerWorld, Thingiverse, Printables, or Cults works fine).
  2. Pick an edge radius. 0.8 mm is a good everyday start.
  3. Choose which edges: leave it on auto for the outer rim and through-holes, or click a specific rim on the 3D preview. You can even paint just a span of one.
  4. Round it, then spin the before-and-after preview to check the result.
  5. Download the rounded STL and open it in Bambu Studio, OrcaSlicer, PrusaSlicer, Cura, or your slicer of choice.

Two ways to round: Fillet rounds the rims in place and keeps embossed detail, and Rebuild flattens a flat part into a clean rounded plate. Fillet is the default and the right pick for almost everything.

Pick the right radius

A small radius like 0.4 mm just breaks a sharp edge. 0.8 mm gives a smoother everyday print. Go to 1.5 mm or 4.0 mm when you want a round-over you can see and feel on a case, handle, holder, or toy. The slider runs the whole range, so you can spread it on as thick as you like.

Fillet, chamfer, bevel, or round-over?

Makers use all four words for the same basic goal: make a sharp edge less sharp. A fillet or round-over curves the edge smoothly; a chamfer or bevel cuts the corner at an angle. ButterySpace produces the curved kind, which feels best in the hand and prints cleanly without supports.

Before you rebuild the model in Fusion 360

Fusion 360, Onshape, FreeCAD, Blender, and Tinkercad are all great tools. But an imported STL usually needs mesh cleanup, conversion, or full remodeling before their fillet tools will touch it, and on a complex mesh the conversion often fails outright. ButterySpace is for the common case: you already have the STL, and you just want the sharp edges softened before printing. If you would rather do it by hand, we wrote up the honest workflows for rounding STL edges without Fusion 360 and without Blender.

Round STL edges, answered

Can you round the edges of an existing STL file?

Yes. That is the whole job here. Upload the STL, pick a radius, and the rims of the model (the outer edge and any through-holes) get a smooth fillet. You download a finished STL, ready to slice.

Do I need to convert the STL to STEP first?

No. The rounding happens directly on the mesh, so there is no mesh-to-solid conversion, no STEP export, and no remodeling. That detour is exactly what this tool exists to skip.

What is the difference between a fillet, a chamfer, a bevel, and a round-over?

They are four words for one goal: make a sharp edge less sharp. A fillet or round-over curves the edge; a chamfer or bevel cuts it at an angle. ButterySpace rounds with a smooth curved fillet, which is the friendliest finish for 3D prints.

Can it round holes and inside edges?

Yes. By default it rounds the outer rim and through-holes automatically. You can also click a specific rim on the 3D preview, or paint just a span of one, and round only that.

Will the rounded STL work in Bambu Studio, OrcaSlicer, PrusaSlicer, or Cura?

Yes. The output is a standard STL, so it drops into mainstream slicers the same way the original did, just smoother.

What edge radius should I use?

Start at 0.8 mm for an everyday print. Use 0.4 mm to lightly break a sharp edge, or go bigger (1.5 mm, even 4.0 mm) for a round-over you can see across the room.

Does this replace Blender or Fusion 360?

For modeling, no. For the single job of softening the edges on a finished STL, it is much faster than either, and you skip the import, conversion, and cleanup steps entirely.

Will it repair a broken or non-manifold STL?

No. The edge rounder rounds existing rims on a sound mesh. If a model is too broken to round safely, the tool tells you clearly instead of handing you a bad file.

Are my uploaded files private?

Yes. Uploads are processed and auto-delete within 24 hours, and they are never sold. If you explicitly opt in to product improvement, we keep that session’s files for up to 30 days and use them to improve the tool.

Still curious? Read how to round STL edges before 3D printing, or smooth your edges now →