A multi-piece board is only as good as its seams. This page shows how to put the pieces together so the front is flush, the holes continue across every seam and the board stays flat on the wall.

Labels and the assembly map

Every piece has a short label engraved on its back — A1, A2, B1… — and the ZIP contains an assembly map (…-assembly.svg) that shows where each piece goes, along with the seams, the anchors, the separators, the overall size and the drilling guide for the anchor rows (see the mounting guide). Raised letters of text boards are separate pieces labelled like their panel plus -L, and the centres of letters such as O or A plus -C; glue them in after the panels are joined (see Raised letters).

Spline strips

The default joint. A shallow recess on the back of both pieces takes a printed strip that bridges the seam; glued in, it makes the two pieces act as one. That is also how a piece without a wall anchor of its own hangs: on its glued strips, from a neighbour that has one (see Strips the app adds). Along stepped seams the strip follows the steps. On curved outlines and small beds the Stepped seam shape can leave more seams than Auto with no room for a strip: the Issues tab names each pair (“No room for a spline strip”), and you glue that seam edge to edge instead.

Section through a spline joint: the strip sits in a recess on the back and keeps the front flush.

Choosing a glue

Material	Glue	Notes
PLA	Medium-viscosity CA (superglue)	Fast and strong. A thin CA wicks too far; gel is harder to spread.
PETG	Two-part epoxy, or CA with a plastics primer	Plain CA bonds poorly to PETG. 5-minute epoxy gives working time; 30-minute epoxy is stronger.
ASA / ABS	CA or epoxy	Both work well.

Glue the strips

Prepare a flat surface bigger than the section you are assembling — a table or the floor covered with cardboard. Flat matters more than anything else.
Lay the pieces face down in their positions (mirrored, see above), seams touching.
Dry-fit every strip. It should drop into its recess with light finger pressure. If it’s tight, take a few strokes off its edges with 240-grit sandpaper.
Clean the surfaces. Scuff the recess and the strip lightly and wipe them with isopropyl alcohol.
Glue. Put a thin line of glue in the recess — not so much that it squeezes out onto the front — and press the strip in.
Check the front. Run a fingertip across the seam from the front side, or look at it from below: the faces must be flush. Push misaligned pieces into line before the glue sets.
Weigh it down with a flat board and a few books until the glue has cured: minutes for CA, as the label says for epoxy. Don’t lift the section before it has fully cured.

Big boards: sections, or on the wall

A glued board is stiff but heavy and awkward to lift. For boards larger than about 2 × 2 pieces:

Glue in sections you can lift and hold level — for example one row at a time — and hang each section.
Or join on the wall. Mount the first piece. Glue the strips into its recesses so they stick out halfway, like tongues. Put glue in the matching recesses of the next piece, press it onto the strips and against the wall, and screw it down. Epoxy gives you the working time this needs.

Bridge strips on straight seams

With the Straight seam shape on the capsule system (see Slicing into pieces), the horizontal seams run through the 5 mm corridor between the slot rows. The walls beside the slots are only about 2.5 mm there: enough for a clean seam, but too thin for a recess along it or for puzzle tabs. Instead, short bridge strips cross the seam on the back. The same happens on any pegboard type whose corridor between hole rows is too narrow for the edge margin but keeps at least 2 mm of wall, such as a Custom type with a staggered grid (a column offset).

Where they go. Each bridge sits in a recess in one of the 15 mm vertical corridors between the slot columns and reaches 25 mm into the piece on either side: 10 × 50 mm by default, one every 40 mm along the seam. They are as wide as the spline width you set (at most 12.4 mm fits on the capsule system). Where one side has less room, on a short row close to the next seam or beside a curved outline, that side reaches less: 20, 15 or 10 mm, down to half the bridge width plus twice the joint clearance (5.3 mm with the defaults). Between two 40 mm rows, for example, a bridge is 30 mm long. A short stretch of seam between a curved outline and a vertical seam gets its bridge at the junction, centred on the vertical seam.
How they print. Identical bridges are one part with a quantity, labelled like the other strips (S1, S2, …): an STL file ending in -x12 means twelve copies, and the 3MF puts every copy on the plates. Print them like spline strips: flat, with 4 walls or 100 % infill.
Where they are glued. The assembly map draws every bridge in its place, dashed like the other strips. Anchors, separators and back labels keep clear of them.
Which boards get them. Spline-strip boards get bridges on every straight seam where one fits. Puzzle boards get them too, because no tab fits the 5 mm corridor; their vertical seams keep the tabs, and a note in the Issues tab says so. Butt boards get them only where a piece would otherwise hang loose (Strips the app adds).
Where none fits. On a curved outline (SVG and Text boards), a piece that is very thin next to the seam, or shares very little seam with its neighbour, may get no bridge: not even the shortest one fits. The Issues tab names the pair (“No room for a spline strip”): glue that seam edge to edge instead.

Where Straight would leave less than 2 mm of wall or cut through holes, it falls back to the Auto seams (stepped horizontal seams). And where straight seams would cut thin slivers off a curved outline, leave out holes that stepped seams keep (for example beside raised letters) or leave a piece that nothing can hold, the app uses the Auto seams instead, for the whole board or a separate part of it. On signs with raised letters, Straight also gives way to the Auto seams when those give more pieces room for a wall anchor or need a narrower margin around the letters, or when straight seams would cut off a sliver or leave out holes that stepped seams keep, even if that takes a wider margin. Each case comes with a warning, and those seams are joined like any other, with no bridges.

Glue the bridges exactly like spline strips, with CA or epoxy in their recesses (see Glue the strips): dry-fit, glue, check the front is flush and weigh the section down. To join a straight seam on the wall, glue the bridges into the recesses of the lower piece so they stick out halfway, then press the next piece onto them, as described above for spline strips.

Puzzle joints

Dovetail tabs lock neighbouring pieces together in the plane of the board. Tabs are only placed in the hole-free corridors, where they reach into the neighbour between its holes — so they never come near a hole.

A vertical puzzle seam on the capsule system: each tab reaches into the neighbour only where its column has a gap between slots.

With the Stepped seam shape on the capsule system the vertical seams step too. Their tabs sit on the straight stretches, pointing either way, or, where those have no room, on a step, pointing up; the pieces interlock on every side, so place each one from the front. On curved outlines and small beds Stepped can leave more seams than Auto with no room for tabs: the Issues tab names each pair (“No room for puzzle tabs”), and you glue that seam instead.

Line the pieces up face to face with the tabs over their sockets.
Press straight in, perpendicular to the board — tabs don’t slide in from the side. Push with your thumbs along the seam, or tap with a rubber mallet over a block of wood.
Glue where it matters. Between pieces that each have their own wall anchors, glue is optional: a drop of CA per tab makes the joint permanent, and without glue the board can be taken apart later. A piece without an anchor of its own hangs on its tabs, so glue its tabs.
Too tight? Scrape the tab edges with a deburring tool. For the next print, raise the joint clearance by 0.05 mm.

Puzzle joints are ideal for assembling directly on the wall: mount one piece, press the next onto its tabs, screw it down, and continue.

Butt joints

With the butt method, pieces simply meet edge to edge and each one hangs on its own anchors — at least two per piece with the default Automatic anchor placement. Line them up carefully with a straightedge across the seam as you screw them down. Butt joints are the quickest to assemble and the easiest to take apart, at the cost of a less rigid board. A piece that would be left without an anchor gets glued strips anyway (below).

Strips the app adds

On Infinite, SVG and Text boards, every piece has to hang on the wall: on an anchor of its own, or through a glued joint to a piece that has one. With butt or puzzle joints, a piece that would otherwise hang loose gets spline strips on its seams — recesses in its back and in its neighbours’, and the strips in the export — and the Issues tab names it. That happens when:

the Fixed grid or your Manual anchors leave the piece without an anchor,
At least one anchor per piece is off in Automatic mode, and the piece is one of those the load doesn’t need an anchor on,
no anchor fits on the piece — a small piece, or one crowded by raised letters.

Strips are only added where a chain of seams leads to an anchored piece: a separate part of the design, such as another word of a sign, needs anchors of its own. With spline strips as the joint, every seam where a strip fits already has one, so nothing is added. On the straight seams of a capsule board (the Straight seam shape), the strips added are bridge strips: butt boards get them only on those pieces’ seams, and puzzle boards already have them on every straight seam.

Glue these strips like any other (see Glue the strips): they carry the piece, so they are not optional. The assembly map shows which pieces have anchors.

Finishing touches

Don’t sand the front face — it carries the build-plate finish. Clean up stray strings with a deburring tool or a sharp blade.
Seams stay visible as fine lines. Borders, hole rings and a textured build plate all make them harder to spot.
Check the board is flat before you mount it: lay it on the floor face down and look for rocking corners.