Print Orientation

What orientation decides

The same model can be printed standing up, lying down or tilted, and each choice gives a different part. Orientation decides:

• Strength. On FDM, where the layer lines run relative to the load.
• Supports. Which surfaces hang over air and need support underneath.
• Surface finish. Which face touches the bed, which faces show stair-stepping and which carry support marks.
• Print time. On FDM, time mostly follows how much path the nozzle has to draw, not just the number of layers, so compare the slicer's time estimate for each orientation.

You rarely get the best of all four at once, so decide which one the part needs most, then set the rest as well as you can.

FDM: strength first for working parts

FDM parts are weaker across their layers than along them. Formlabs notes the layers are not bonded together as strongly as the extruded lines, and Prusa's design guide says structural parts should be printed in the orientation that best serves their strength. The background is in The Three Axes and Layer-by-Layer Printing.

To use that:

1. Work out how the part will be loaded: pulled, bent, twisted or pressed.
2. Picture where it would snap. That line should cross many continuous strands, not run along a single layer boundary.
3. Rotate the part so the layers run along the direction of the load.

Examples: a hook printed standing up, with its layers stacked through the curve, puts the weak layer bonds right where it bends. The same hook printed on its side has the curve drawn in each layer. A peg or pin that must not snap is usually better lying down than standing up. A bracket that will be bent should have its bend inside the layers, not across them.

FDM: the face on the bed

Prusa notes that a surface printed directly on the print bed is perfectly flat and smooth, while surfaces printed over supports do not get the same finish. So:

• Put the largest flat face down, where it gets the flat bed finish and needs no support.
• If one face must look good, consider putting it on the bed, or facing up as a top surface, rather than over supports.
• Rounded bottom edges are steep overhangs right at the bed. Prusa's guide recommends a chamfer instead of a fillet on edges facing the bed when finish matters.

First layer setup is covered in First Layer Fundamentals.

FDM: fewer supports

Every overhang that is too steep needs support, and support costs time, material and surface quality. Prusa's design guide shows the simple case: a flat, fence-like part designed to print upright is better printed lying down. When an orientation still needs a lot of support, Prusa suggests splitting the model into pieces that each print well, then gluing them, with pegs for alignment. Rotate the part in the slicer and watch how the support preview changes. See Supports and Overhangs.

FDM: surface and time

For FDM, check the slicer's time estimate for each orientation rather than assuming fewer layers is faster. How visible the layers are on curved and sloped faces depends on layer height as well as orientation; see Choosing a Layer Height.

Resin: a different set of rules

Formlabs reports that its SLA resin parts are close to equally strong in every direction, so on those resins strength rarely decides orientation; check your own resin's data sheet. Prusa's guide for its SL1 and SL1S printers says orientation is crucial for print quality and gives the main reasons:

• Peel force. Large flat horizontal surfaces need a lot of force to separate from the bottom of the tank after each layer. Tilting the part reduces the area cured in any one layer.
• Supports. A tilted part covers a larger area, so its supports spread out more evenly. Rotate it to minimize the points where a layer would start in mid-air.
• Anti-aliasing. Prusa lists better anti-aliasing among the benefits of tilting.
• Time. Prusa gives the print time as below, and notes that a tall object prints faster laid flat. The number of parts on the platform does not change the time.

Prusa notes that resin prints are often placed at about a 45 degree angle Rule of thumb, and that some objects do better directly on the platform. Its slicer's automatic orientation offers three goals: best surface quality, reduced overhang slopes (fewest supports), or lowest Z height (shortest print). Pick the goal the part needs, then check the result yourself. Resin orientation and support placement go deeper in Resin Orientation and Supports.

A quick routine

1. Decide what matters most: strength, appearance or speed.
2. FDM: find the load direction and lay the layers along it. Resin: tilt the part and keep detailed faces away from where supports will touch.
3. Put a flat face on the bed if there is one (FDM).
4. Check the support preview and the time estimate in the slicer, and try a second orientation for comparison.
5. If no orientation works, split the model.