Splitting Oversized Models and Registration Pins

When to split

Prusa's cut tool documentation lists the usual reasons: the model is too big to print in one piece, you only want part of it, a part needs a different orientation for strength, or printing it whole would need a needlessly large amount of support. Bambu adds easier sanding, painting and assembly. Splitting is often the best fix for a support-heavy model even when it fits the printer. For prints that fill the whole build volume, see Large-Format Printing.

Where to cut

• Flat, hidden or natural seams. A joint along an existing edge, a change in shape or the underside hides best. Prusa notes that seams show more on small models than on large ones.
• Cut face down. A flat cut face sitting on the bed prints flat and accurate, which is what you want for a glued joint. Both slicers below can place a part on its cut face.
• Orientation of each piece. After cutting, each part can be oriented on its own for strength and fewer supports; see Print Orientation.
• Enough material at the joint. A pin needs solid wall around it. Avoid cutting through thin sections.

Cutting in the slicer

PrusaSlicer

Select the object and press C or pick the Cut tool from the left toolbar. You can type an exact Z position, rotate the plane with the widget arrows, or hold Shift and click two points to define a plane perpendicular to the view.

• Planar mode makes a straight cut. Dovetail mode makes a trapezoidal pin and tail on the cut plane, with adjustable dimensions.
• Connectors (Planar mode): left-click to add, right-click to remove. A Plug adds a peg to one side and subtracts the space for it from the other. A Dowel subtracts a hole from both sides and generates a separate pin to print. A Snap adds a snap-fit connector on one side and the matching space on the other. You can set style, shape, depth, size and rotation, and Flip cut plane swaps which side gets the plug.
• After the cut, each new object can keep its orientation, be placed on its cut face, or be flipped.

Bambu Studio

Bambu Studio's planar cut tool also opens with C. It offers Planar and Dovetail modes; dovetails have adjustable Depth, Width, Flap angle and Groove angle. It adds Plug, Dowel and Snap connectors, and after cutting you can keep orientation, place on cut, or flip each part. Height (the absolute position of the plane) can only be set when the plane is parallel to the bed. Bambu notes that a dovetail cut may leave non-manifold edges and prompt you to fix the model before slicing; do so, and see Meshes, Manifolds and Normals for what that warning means.

Cutting in Blender

Use a modeling program when you want control over the joint shape or plan to share the parts as files.

1. Duplicate the object so you have one copy for each side of the cut.
2. In Edit Mode, select all and use Mesh, Bisect. Drag the cutting line in a view where the plane appears as a line; hold Ctrl to snap the angle to 15 degree steps. Set exact values in the Plane Point and Plane Normal fields of the adjust-last-operation panel.
3. Turn on Fill, which creates new faces along the cut, and Clear Outer on one copy and Clear Inner on the other. Without Fill, each half is left open along the cut and is not printable.
4. Check each half for non-manifold edges before you export.

Registration pins and joints

A pin keeps glued parts aligned while the glue sets and adds strength across the seam. Prusa's modeling guide suggests modeling in pegs for alignment and strength.

• Separate dowels. Holes in both halves and a printed (or bought) pin. Both cut faces stay flat, which is easiest to print. The slicer Dowel connector does this for you.
• Plugs. A peg on one half, a socket in the other. One face is no longer flat, so print that half with the peg pointing up.
• Dovetails. Slide-together joints that resist pulling apart in one direction.

To make pin holes by hand in Blender, place a cylinder where the pin goes and use a Boolean modifier with Difference on each half. Blender's manual warns that only manifold meshes are guaranteed to give proper results, and that the Manifold solver does not work at all on non-manifold meshes, so check the halves first.

An alignment pin wants a snug fit: loose enough to go in, tight enough not to wobble. There is no universal number, so print one pin and one short section of the joint first and adjust Measure it. See Fits and Tolerances.

Joining the parts

Prusa's advice for an invisible seam: glue surfaces should be smooth and free of grease or dirt, light sanding can help adhesion, and very viscous superglue may not suit rough surfaces. Use the glue's own label or SDS for ventilation and skin protection. Adhesive choice and clamping are covered in Gluing and Joining Parts.