How to join 3D printed parts: glue by material, pegs, dowels, magnets, screws and inserts
Quick answer: for PLA and PETG, use cyanoacrylate (super glue) on sanded, clean faces and clamp for a minute. For ABS and ASA, acetone brushed on both faces welds the plastic itself and nearly hides the seam. Glue alone is weak in peel, so give the joint something mechanical. Use press-fit pegs (0.1–0.2 mm clearance in PLA, more in PETG and ABS), a dovetail or dowels. Use magnets for parts that come apart, and screws into heat-set inserts for anything structural. Pegs plus CA is the right default for a split print. A splitter can place and size all of these when it cuts the model, with a label sheet for reassembly.
- Prusa's tensile tests put CA on PETG at about 13 MPa and on PLA at about 10 MPa; polystyrene model cement did not bond PETG or ASA at all.
- PETG is the hard one: no hobby solvent dissolves it, so it is CA or epoxy, with sanding.
- Clearance, not glue, decides whether pieces go together: a 5 mm peg wants a 5.2–5.4 mm socket in PLA, 5.7 mm in PETG, 6 mm in ABS — then test one joint before printing twenty.
First: a mechanical joint, then glue
A butt joint of two flat faces held with glue fails in peel: the load concentrates on one edge and unzips the bond. That is why split prints are joined with something that locates and holds the parts (pegs, dowels, dovetails, fingers) and glue is used to fix them in place, not to carry the load. The joint also aligns the pieces while the glue sets, which matters more than it sounds: a 0.3 mm step on a seam is visible from across the room; a peg makes it impossible.
Glue by material
| Material | Best | Also works | Avoid | Notes |
|---|---|---|---|---|
| PLA | Cyanoacrylate (CA / super glue) | Epoxy (5-minute), polyurethane, acetone (bonds, does not smooth) | Hot glue for anything structural; CA accelerator spray near thin parts (heat deforms PLA) | CA on a lightly sanded face is the strongest easy bond. Clamp 30–60 s. |
| PETG | CA, after sanding both faces | Two-part epoxy; methacrylate structural adhesives | Model cement (zero bond in Prusa's test), plumber's PVC cement, any solvent "weld" | No hobby solvent touches PETG. Scuff with 120–240 grit, wipe with isopropanol, then CA. |
| ABS / ASA | Acetone solvent weld | ABS cement, "ABS juice" (scrap dissolved in acetone), CA, epoxy | Soaking the parts — acetone softens edges and detail | Brush acetone on both faces, press, hold 60 s, leave 24 h. The seam can be sanded almost invisible because it is the same plastic. |
| TPU / flexible | CA on stiffer TPU (95A) | Contact cement for soft grades | Epoxy (too rigid, cracks at the bond line) | Flexible joints need flexible glue; mechanical joints (lacing, pegs) hold better than any adhesive. |
| Nylon / PA | Two-part epoxy after sanding and flame or primer treatment | Mechanical joints (inserts, screws) are far more reliable | CA alone on unprepared nylon | Low surface energy; nothing bonds well. Design for screws. |
| Resin (SLA / MSLA) | Uncured resin at the joint, then UV cure | CA, epoxy | Anything on an uncured, tacky surface — wash and cure first | A resin joint cured under the lamp is as strong as the part. Resin parts are brittle: pegs, not screws. |
Preparation is the same for every glue: flat, clean, dry. Sand the mating faces so they touch everywhere (a cut face from a splitter already is), blow off the dust, wipe with isopropanol, and press hard enough that glue squeezes out of the seam. Glue what you can see: a drop at the centre of each face spreads outward without running down the outside.
Which glue to buy
The products below are the ones the table above points to, by material. They are widely sold and in stock; the links search Amazon so you see current listings and prices.
| Material | Buy | Why |
|---|---|---|
| PLA | Gorilla Super Glue Gel · 3D Gloop! PLA · Starbond medium CA + activator | CA gel for most joints; Gloop for the strongest bond; thin CA + activator for instant tacks (activator off thin walls). |
| PETG | 3D Gloop! PET/PETG · Loctite Plastics Bonding System · Gorilla 2-part epoxy | Gloop is the one glue made for PETG; the Loctite kit adds a primer so CA grips; epoxy for big faces. |
| ABS / ASA | 3D Gloop! ABS/ASA · Pure acetone · Oatey ABS cement | All three solvent-weld the plastic; acetone is cheapest and leaves the cleanest seam. |
| TPU | Loctite Vinyl, Fabric & Plastic · E6000 · Loctite Super Glue Ultra Gel | Flexible parts need a flexible glue; rubber-toughened CA for stiffer 95A. |
| Nylon | Loctite Plastics Bonding System · J-B Weld PlasticBonder | Primer, or a structural two-part; sand first either way. |
| Resin | UV resin + UV torch · Gorilla Super Glue Gel | Uncured resin cured with a lamp is as strong as the part. |
| Every job | Small spring clamps · Sanding sponges 120–400 · 99% isopropyl alcohol | Clamp, scuff, wipe: preparation decides the bond more than the brand. |
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Connectors: what to use when
| Joint | Use when | Holds against | Needs |
|---|---|---|---|
| Press-fit pegs (square, 2–4 per face) | Any split print; the default | Shear and alignment; pull-apart with glue | Printed pegs; 0.1–0.2 mm clearance (PLA) |
| Dowels (round, bought or printed) | Long seams, wood-like assemblies | Shear | 3–6 mm dowel; round holes are easy to drill out if tight |
| Dovetail | Thin walls where a peg would split the wall; parts that slide on | Pull-apart and shear, no glue needed | Cuts on one axis only; a few tenths of clearance |
| Finger / box joint | Long flat cuts; maximum glue area | Everything, once glued | Clean print of the fingers; glue |
| Magnets (6 × 3 mm disc is the common size) | Parts that come apart: lids, display busts, swappable heads | Pull-apart (weakly), alignment | Pockets 0.1 mm over the magnet; CA; mind the polarity |
| Screws + heat-set inserts | Anything that carries load or is opened again | Everything, repeatedly | A wall thick enough for the insert; iron; the screw reaches from outside one piece into the other |
| Jigsaw / puzzle cut | Flat panels, signs, tiles | Pull-apart and shear, no parts to print | Pieces slide in from the side; 0.2–0.3 mm clearance |
Clearance: the number that makes or breaks the fit
Printed holes come out smaller than modelled and printed pegs come out larger, by an amount that depends on the material's shrinkage, the nozzle, and whether the hole is vertical or horizontal. The clearances below are the splitter's defaults for a press fit (added to the socket's radius, so double them for the diameter), and they are a starting point, not a law: print one joint first.
| Material | Press fit (per side) | Glue / slide fit (per side) | 5 mm peg → socket |
|---|---|---|---|
| PLA | 0.10–0.20 mm | 0.30–0.40 mm | 5.2–5.4 mm press, 5.6–5.8 mm glue |
| PETG | 0.35 mm | 0.45 mm | 5.7 mm |
| ABS / ASA | 0.50 mm | 0.60 mm | 6.0 mm |
| TPU | 0.30 mm | — | 5.6 mm (the peg compresses) |
| Nylon | 0.40 mm | 0.50 mm | 5.8 mm |
| Resin | 0.10 mm | 0.20 mm | 5.2 mm |
Three details that matter more than the third decimal: a hole printed horizontally (its axis parallel to the bed) is slightly oval and tighter at the top, so give it 0.1 mm more; a square peg cannot rotate and is more forgiving of a loose fit than a round one; and a 1 mm chamfer on the peg tip makes a tight joint go together without a mallet.
Heat-set inserts and screws
For a joint that must carry weight or be opened, put a brass heat-set insert in one piece and run a machine screw through the other. The rules from CNC Kitchen's tests: make a blind hole about 1 mm deeper than the insert; print a test strip of holes and pick the smallest diameter that lets the insert seat without a burr (an M3 insert typically wants a hole between 4.0 and 4.4 mm depending on the insert and the printer); set the iron 10–20 °C above the printing temperature (about 225 °C for PLA, 245 °C for PETG, 265 °C for ABS); melt the insert 90 % of the way in, press it home flat and hold it for a few seconds so it does not creep back out. Leave at least two perimeters of wall around it. The screw itself needs a clearance hole (M3: 3.4 mm) and, for a flush finish, a counterbore for the head; a splitter's screw-joint mode generates hole, counterbore and insert pocket together, placed only where one piece is thin enough for the screw to reach.
Hiding the seam
Once the pieces are joined, the seam is a hairline where two caps meet. Three ways to make it disappear, in increasing effort: run the joint through a wavy or zigzag cut instead of a flat one, which hides the line in the surface; fill with the same material (a 3D pen, or "ABS juice" on ABS) and sand through 240–400 grit; or fill with a sandable automotive filler and prime. Decide this before cutting: a seam placed across a flat band or a natural edge of the model takes two minutes to hide, and one across a face or a curved detail takes an hour — a seam-aware splitter scores each cut position for exactly this.
Frequently asked questions
What is the best glue for joining PLA 3D printed parts?
Cyanoacrylate (super glue) on lightly sanded, clean faces, clamped for about a minute. Prusa's tensile tests measured around 10 MPa for good CA brands on PLA. Epoxy and polyurethane also work; avoid relying on hot glue, and keep accelerator spray away from thin PLA because the heat deforms it.
What glue works on PETG?
Super glue after sanding both faces with 120–240 grit and wiping with isopropanol, or a two-part epoxy for larger areas. No solvent available to hobbyists dissolves PETG, and polystyrene model cement does not bond it at all, so a mechanical joint (pegs, dowels, screws) matters more on PETG than on any other material.
Can I glue ABS with acetone?
Yes — acetone dissolves ABS and ASA, so brushing it on both faces and pressing them together welds the plastic itself. Keep it off detail you want to keep, hold the parts for a minute and leave them a day; the seam can then be sanded almost invisible.
How much clearance do pegs need in 3D printed parts?
For a press fit, about 0.1–0.2 mm per side in PLA (a 5 mm peg in a 5.2–5.4 mm socket), roughly 0.35 mm in PETG, 0.5 mm in ABS and 0.1 mm in resin. Holes printed horizontally need about 0.1 mm more. Print one test joint before printing the whole set.
Magnets or pegs for a 3D print that comes apart?
Magnets, in pockets about 0.1 mm larger than the magnet, glued with CA, with the polarity checked before the glue sets. A 6 × 3 mm disc holds a display part; anything that carries load or gets knocked needs pegs or screws instead, and a peg alongside the magnets gives alignment while the magnets give the hold.
How do I hide the seam on a glued 3D print?
Fill the hairline with the same plastic (3D pen, or acetone slurry for ABS) or a sandable filler, sand through 240–400 grit and prime. Choosing a wavy cut, or a cut position on a flat band or natural edge, makes the seam far easier to hide than a flat cut across a detail.
Sources
- Prusa Research, The great guide to gluing and assembling 3D prints (Feb 2021) — adhesive types, tensile test table (CA on PET ≈ 13 MPa, PLA ≈ 10 MPa; Revell Contacta 0 on PET and ASA), surface preparation. Read 13 Oct 2026.
- Clever Creations, How to glue 3D prints: the best glue for PLA, PETG and ABS (updated Mar 2024) — per-material recommendations, acetone on ABS, PETG limits. Read 13 Oct 2026.
- CNC Kitchen, Tips and tricks for heat-set inserts (Oct 2021) — hole depth, test-strip sizing (M3 test holes 4.0–4.4 mm), iron temperatures 10–20 °C above printing temperature, 90 % melt-in. Read 13 Oct 2026.
- splicestl, joinery documentation — the material tolerance presets (PLA 0.20, PETG 0.35, ABS/ASA 0.50, TPU 0.30, resin 0.10, nylon 0.40 mm per side) used in the clearance table; defaults, to be confirmed with a test joint on your printer.
What changed — 13 October 2026: first published.