Most quote rejections are not about your design — they are about small file issues that could have been fixed in 30 seconds. Run this checklist before you upload anything.
1. Is the mesh closed (watertight)?
Every face has to connect to exactly two edges. Holes in the mesh confuse the slicer and result in incorrectly filled parts. Most CAD tools have a "Check for holes" or "Close mesh" command. In Blender, use 3D Print Toolbox. In Meshmixer, Analysis → Inspector.
2. Are the normals pointing outward?
Flipped normals mean the slicer thinks the inside is the outside and will try to print your part inside-out. In most tools, run Recalculate normals or check the "all outside" option before export.
3. Is your unit set to millimeters?
STL files don't store units — they are just numbers. If you exported in inches, a 2-inch part becomes a 2-millimeter part. Always verify scale after export by checking the bounding box.
4. Are wall thicknesses above the minimum?
Rule of thumb minimums:
- FDM: 1.2 mm
- SLA: 0.8 mm
- SLS: 0.8 mm
Thinner walls will either not print at all or break during post-processing.
5. Are holes and slots larger than 2 mm?
Small holes collapse. If you need smaller precision features, note in the quote that you want them drilled or reamed post-print.
6. Are text features at least 1 mm deep and bold?
Engraved text under 1 mm depth reads as mush. Bold sans-serif fonts at 8pt+ work best; script and thin fonts do not translate to 3D prints well.
7. Did you triangulate appropriately?
Too few triangles and curves look faceted. Too many and file uploads take forever and crash slicers. Aim for chord tolerance of 0.05 mm and angle tolerance of 5° when exporting from CAD.
8. Is the file under 100 MB?
Bigger files work but slow everything down. If your file is over 100 MB, you probably over-triangulated — re-export with looser tolerance.
Quick fix tools
- Meshmixer (free) — auto-repair holes, reduce poly count
- Netfabb Basic (free tier) — one-click mesh repair
- PrusaSlicer — slice and preview before sending
- Microsoft 3D Builder — simple repair for Windows users