How to print an object bigger than your printer

Scale it down or split it?

First, does the object need to be this big? Scaling down is one click in any slicer and keeps the model in one piece: the right call for a display piece, as long as thin walls and small details stay printable.

Split when size matters: a helmet that must fit a head, a part that mates with something real, a full-size prop. Splitting keeps every detail and the true dimensions, at the cost of some assembly. On a 180 mm printer such as the A1 mini or MINI+, or a resin printer like the Saturn 4 Ultra, this comes up all the time. Load the file in our free STL viewer first: it shows the real dimensions and which printers it fits on. A model a few millimetres too tall often fits diagonally or lying down.

Choosing where to cut

Where the seams go decides how the finished piece looks. Good places to cut:

• Natural joints: neck, wrists, waist, the line between a figure and its base, a change of colour. A seam there looks intended.
• Flat or simple areas: a flat surface is easy to fill and sand, while a seam through fine texture, a face or lettering is hard to hide.
• Hidden sides: the back, the underside, the inside of a helmet.
• Thinner cross-sections: a smaller cut face means a shorter seam to finish, as long as it leaves room for connectors and glue.

Use as few cuts as the build volume allows and keep them parallel to the main axes where you can: parts align and print more easily. In SplitSTL, smart cuts move planes toward thinner sections automatically, and the Pro mode cuts at natural joints such as the neck, arms or base instead of a straight grid. See also splitting a cosplay helmet.

Orienting each part

• A cut face on the plate is usually best: it is flat, sticks well and needs no support, and the seam edge is the crisp first layer.
• Check overhangs: sometimes another face needs less support.
• Think about strength. Layer lines are the weak direction, so a thin part under load, such as a blade or a handle, should have its layers running along its length.
• Resin parts are usually tilted and supported, so the flat face matters less there. Keep supports off the cut face so it stays flat for gluing.

Connectors and tolerances

• Pins or dowels: holes in both parts and a separate pin. Simple, strong and the default for glued builds; wooden dowels or metal rods of the same diameter work too.
• Integrated pegs: a peg on one part, a hole in the other. No loose pins, but that part can’t print flat on its cut face.
• Magnets: pockets on both sides for a build you can take apart. Check the polarity before gluing them in.
• Glue only: fine for small, light parts with large flat contact faces.

Printed holes come out smaller and pins larger than designed, so connectors need clearance, and the right amount depends on your printer, nozzle and material. Don’t guess: print our free tolerance test once per printer and material, and use the tightest clearance that still assembles by hand. Our comparison of dowels and magnets goes further.

Estimating material and planning the prints

• Check the volume and estimated weight in the STL viewer, then work out the cost with our 3D printing calculators.
• Have enough filament from one batch: shades can differ between spools, and a colour change halfway up a model is obvious.
• If the file shows holes or errors, fix it before splitting; see repairing a non-manifold STL.
• Print one part with connectors first, check the fit, then print the rest.

Gluing, sanding and filling seams

1. Dry-fit every part. Sand high spots and any elephant’s foot on the cut faces until the parts sit flush.
2. Glue: cyanoacrylate for quick bonds on PLA, two-part epoxy for large or load-bearing joints, since it also fills small gaps. ABS and ASA can be solvent-welded with acetone, and resin parts can be joined with a little of the same resin cured under UV light.
3. Fill the seam line with putty or filler, let it cure, then sand flush, working up through the grits.
4. Spray a filler primer to reveal what is left, fill and sand again, then paint.

More in our guide to gluing and finishing seams.