Start from how the part is built, not how it is drawn
A layer-built part is a stack of extruded, fused cross-sections. Almost every design decision that matters follows from that one fact: the part is strong along a layer and weak between layers, overhangs need support that must be removed and leaves a mark, and the first layer’s contact area decides whether the part survives the build at all.
Walls
Design to the minimum wall for the process, which the FDM process page reads from the live catalogue rather than quoting from memory. Two practical points the figure does not tell you:
- A wall exactly at the minimum is a single extrusion wide, so it has no infill and no redundancy. If the wall does anything structural, go at least fifty per cent above the minimum.
- The thin-wall figure we report for your uploaded mesh is a ray-sampled estimate, not a measurement, and it is labelled as an approximation everywhere it appears. Use it to find the region worth checking in CAD, not as a QA result.
Overhangs and support
Support costs money twice: material that is printed and thrown away, and labour to remove it. It also leaves a mark on the supported face. The part is sliced and priced the way you uploaded it; the quote also scores other orientations on support volume, contact area and height, but only as a recommendation — and it does not know which face you think of as the show face.
So design the cosmetic face so it does not need support: facing up or standing vertical. Self-supporting geometry — chamfers instead of horizontal overhangs, teardrop instead of round horizontal holes — usually removes the problem outright rather than reducing it.
Holes, threads and fits
Vertical holes print undersized and slightly out of round; horizontal holes sag at the top. If a hole is a bearing seat or a dowel fit, the reliable answer is to print it undersize and drill or ream it. Threads under about M6 are more reliable as a heat-set insert than as printed geometry.
A clearance fit that works in a machined part will be tight in a printed one. Start from 0.2–0.3 mm diametral clearance on a sliding fit and adjust from a test part; this is a rule of thumb, not a specification, and it moves with material and layer height.
What actually makes it expensive
Not volume — machine time and plate occupancy. A tall thin part occupies the full height of a plate for hours and leaves the rest of the plate empty. The same part laid down may nest fifteen to a plate. That is why the quantity break table on a quote is real rather than a discount curve: the unit price falls because the plate fills.
If a part is expensive and you do not know why, look at the reported parts-per-plate and plate count before you look at the material.
Before you upload
- Export in millimetres. STL and OBJ carry no unit, so they are read as millimetres; if the size shown looks wrong, change the unit next to it.
- Watertight, manifold, no inverted normals, no stray shells.
- Mesh resolution fine enough that curves are curves, coarse enough that the file is not hundreds of megabytes of triangles describing a flat face.
- One part per file unless the parts are genuinely a single assembly.