Large Prints and Multi-Part Assemblies

Whole or in pieces

The first question is whether the model fits the build volume at the size you want. The build fit calculator at the end of this page checks a model's dimensions against your printer's, including turned on its side. Leave room for a brim, and use the build volume your printer maker publishes Maker spec.

Even when it fits, splitting is often the better plan:

• Better orientation per piece. Prusa's design guide points out that splitting lets each part be oriented for better results and fewer supports.
• Strength. Each piece can be laid so its layers follow its own load; see Orienting Parts for Strength.
• Risk. A failure late in a very long print loses all of it. Several shorter prints put less at stake each time.
• Warping. A smaller footprint is easier to keep flat, as below.

The cost of splitting is a seam and assembly time. Prusa notes that seams are more visible on small models, so splitting pays off most on big ones.

Where to cut

• Along a natural line: a panel edge, a change of shape, the underside of a ledge, or anywhere the seam will be hidden or painted over.
• So each piece has a flat face to sit on the bed. Prusa's cut tool can place each new piece cut face down on the print surface, which turns the cut itself into the flat base.
• Away from the highest stress. A glued seam in the middle of a bending load is the first place it will break.
• Into pieces of sensible size for your printer, not just barely under the limit.

Model-level splitting, registration pins and keys are covered in Splitting Oversized Models and Registration Pins.

Cutting in the slicer

PrusaSlicer's Cut tool, as Prusa documents it, offers these options:

Option	What it makes
Planar cut	A straight cut at a height you type in, rotatable to any angle
Plug connector	A peg on one side and a matching hole subtracted from the other
Dowel connector	Holes in both sides and a separate pin printed as its own object
Snap connector	A snap-fit on one side and the space for it on the other
Dovetail	A trapezoid pin and tail across the cut

You can set the connector style, shape, depth and size. Prusa's article gives no fit tolerance for the connectors, so do not assume they will fit on the first try. Cut a small test section with one connector, print it, and adjust before printing the full pieces Measure it. How much gap a peg needs in your material is covered in Designing Fits and Clearances. Other slicers have similar cut tools; check their documentation for the options.

Stopping big parts from warping

Prusa's warping article says that with large objects the corners can lift from the bed, mostly with high-temperature materials such as PC Blend, ASA or ABS. Its advice, which applies most to big footprints:

• Use a brim to increase adhesion to the print surface. See Brims, Rafts and Skirts.
• Add small helper shapes, such as a thin cylinder, at the corner that lifts if a brim is not enough.
• Use a draft shield (a printed wall around the part) to hold heat around it.
• Orient the problem areas toward the center of the heatbed.
• Enclosure for hot materials. Prusa suggests an enclosure if you print ABS, ASA or PC Blend most of the time, but warns that printing PLA or PETG in an enclosure might not be a good idea, since those need a lot of cooling.
• Check cooling. Prusa's advice to check that the print fan is on and try a higher fan speed is for PLA and PETG, which need a lot of cooling. For ABS or PC Blend it suggests trying the fan only at low speeds, and it warns that too much fan speed may warp and lift the whole object and weaken layer bonding. Follow the filament maker's cooling guidance.

If corners still lift, work through Warping in order. Splitting a long flat part into shorter pieces is also a valid fix.

Before you start a long print

1. Watch the first few layers. A first layer that is not right will not get better over a long print; see First Layer Fundamentals.
2. Check the slicer's filament estimate against what is left on the spool, plus a margin.
3. Make sure nothing on or around the printer can snag the moving parts over many hours, and follow your printer maker's guidance on unattended printing.
4. Print a small section of the riskiest feature first, such as a large overhang, if you are unsure.

Joining the pieces

Prusa's guide gives a few assembly points: glued seams should be clean and free of grease or dirt, light sanding can help adhesion, alignment pegs add strength and help line parts up, and superglue can be very viscous, so it may not suit rough surfaces, and it can leave traces. Adhesive choice, clamping and the ventilation each glue's label calls for are in Gluing and Joining Parts.