Two identical STL files can produce wildly different parts depending on how they are oriented in the printer. Here is what every buyer and maker should know.
Strength is directional on FDM and SLA
Layer-line parts are up to 40% weaker across layers than along them. If your part has a known load direction, print it so that the load runs along the layers, not across them.
Example: A hook that will hold a 5 kg weight should be printed lying flat, so layers stack across the hook's width, not along its length.
Surface quality is best on top and worst on overhangs
- Top surfaces (facing up) print cleanest on FDM.
- Bottom surfaces touching the build plate are flat and shiny on SLA but can show bed texture on FDM.
- Overhangs past 45° need support material, which leaves scars when removed.
If a face is going to be visible in the final product, orient the part so that face is either on top or vertical — never sitting on supports.
Cost scales with support volume
Support material is the #1 hidden cost on SLA and resin prints. A 50 mm cube printed corner-up on SLA can use more support than actual part. The same cube printed flat uses almost none. Smart orientation cuts cost by 20–50%.
Layer lines follow the XY plane
Round holes printed vertically (axis aligned with Z) come out as "staircase" approximations. If you need a precision hole:
- Print small holes vertically and ream them afterwards, or
- Orient the part so the hole axis is horizontal (XY plane), where the slicer uses arcs instead of steps.
Let the maker choose — usually
Experienced makers know their machines and will orient your part for the best tradeoff between strength, surface, and cost. Unless you have a specific requirement ("hide layer lines on this face" or "this needs to be strongest in Y"), let them decide and save money.
When to specify
- The part has a critical visible face
- The part has a known load direction
- A hole or mating feature needs specific tolerance
- The part has thin walls that must stay dimensionally accurate
In any of these cases, add a note to the quote request describing the requirement — makers will orient accordingly.