Designing Jigs and Fixtures for FDM 3D Printing

Jigs and fixtures are some of the best jobs for an FDM printer. They are one-off or low-volume, they are shaped around a specific part, and they usually need to exist by tomorrow, not next month. A printed drill guide, assembly nest or set of soft jaws can be designed in an afternoon and in your hands a day or two later.

This guide covers what makes a printed jig work: picking the material, the design rules that matter, soft jaws, alignment features and inserts, plus how to get one made quickly.

Why FDM Suits Jigs and Fixtures

FDM suits jigs and fixtures because they are custom shapes made in small numbers, which is exactly where printing beats machining. A few reasons it works well:

• It follows your part. You can offset the part's own CAD to make a nest, so the jig matches the geometry exactly, curves and all.
• It is cheap to change. If the first version is slightly off, you edit the model and reprint. No new stock, no new setup.
• It is light and kind to surfaces. Plastic jigs are easy to handle all shift and less likely to mark finished parts than steel.
• It is fast. Most of our orders are ready within 24–48 hours, and short prints can often be collected the same day.

As a rough rule, a jig is a guide that controls where a tool goes (a drill guide, a marking template). A fixture holds the workpiece in place while you work on it (an assembly nest, a gluing cradle, a vice insert). The design rules below apply to both.

Pick the Material for the Job

Pick the material by asking three questions: how hot does it get, how much load does it take, and does it need to flex? Here is how our materials line up for shop-floor tooling.

Material	Use it for	Watch out for
PLA	Trial fits, go/no-go checks and test versions at room temperature	Softens around 55–60 °C and can snap under sharp impact
PETG	Everyday jigs, drill guides, assembly nests	Heat limit of about 80 °C
ASA	Fixtures near warm equipment or used outdoors	Around 100 °C, so not for hot tooling
Nylon	Clamps, clips and parts that flex or wear	Slightly flexible, so less stiff than the carbon-fibre grades
PA-CF	Stiff, light jigs and structural fixtures	Good to about 150 °C; matte black only
PAHT-CF	Fixtures in hot or humid spots	Holds its shape to about 180 °C
PPA-CF	Our stiffest option, near oils, fuels or heat past 200 °C	More brittle than nylon, so snap-fits can crack
PPS-CF	Chemical exposure, very high heat (~260 °C)	Brittle, so best for static parts
TPU	Soft jaw pads, grip faces, non-marring nests	Flexible by design, so not for locating faces

PETG is a sensible default for most jigs. Step up to PA-CF when stiffness matters, for example a long drill guide that must not bow. All four carbon-fibre materials carry a flat handling fee for drying and a hardened nozzle, shown separately on your quote.

Design Rules That Make Jigs Work

Allow for print tolerance

Typical FDM tolerances are ±0.2–0.5 mm, and holes tend to come out 0.1–0.2 mm smaller than designed. Offset your nest from the part by a small clearance rather than modelling it to zero. If a dimension really matters, tell us which one when you order, so we know where to focus. Our FDM design reference has starting values for different fits.

Locate on a few points, not a full outline

A nest that hugs the whole perimeter of a part is over-constrained. Any small error and the part jams. The classic approach is 3-2-1 location: three contact points on the main face, two on a side, one on the end. Use small pads or ribs as contact points and leave clearance everywhere else.

Relieve the inside corners

A printed inside corner always has a small radius, but a machined or sheet-metal part often has a sharp edge. Add a small relief cut or round pocket in each inside corner so the part sits flat against both faces.

Add lead-ins

Chamfer the entry edges of every pocket and hole. A 0.5–1 mm chamfer guides the part in and saves operators from fiddling.

Use ribs, not solid blocks

For functional parts, walls of 1.6–2.0 mm are a good baseline. Rather than printing a thick solid block, use ribs and moderate infill. Our guide to infill explains the trade-off between strength, weight and cost.

Think about layer direction

Printed parts are weakest between layers. Orient the jig so the main load runs along the layers, not across them, and keep critical locating faces flat on the build plate where possible, as that is usually the flattest surface.

Soft Jaws for Vices

Printed soft jaws hold awkward or finished parts without marking them. A few tips:

• Model the jaw pocket from the part's own geometry, then offset it by a small clearance.
• Use PETG or PA-CF for the jaw body and add a TPU pad where the part needs extra grip or protection.
• Add pockets for small magnets if you want the jaws to stick to a steel vice. Size the pocket to the magnet maker's dimensions plus a little clearance.
• Keep clamping force moderate. Plastic jaws hold well, but they will creep under heavy clamping over time.

Alignment Features and Wear

For anything located hundreds of times, let metal take the wear and plastic do the shaping:

• Dowel pins: design holes slightly undersize and press in steel dowels rather than relying on printed pins, which wear and snap.
• Drill bushes: a drill bit will quickly wear a plastic guide hole oversize. Press a steel drill bush into the guide instead.
• Reaming: for a precise hole, print it slightly undersize and ream it to size afterwards.

Threads and Inserts

Printed threads work best at M6 and larger. For smaller fasteners, use heat-set brass inserts or self-tapping screws. Design the insert pocket to the insert maker's recommended size, and leave enough wall around it (at least the 1.6–2.0 mm functional baseline). You press the inserts in after printing with a soldering iron and an insert tip.

Checklist Before You Upload

• Material chosen for the temperature, load and flex the jig will see
• Clearance added to nests and pockets, not modelled to zero
• Locating points defined, with clearance elsewhere
• Inside corners relieved and entry edges chamfered
• Holes for dowels, bushes or inserts sized to the hardware
• Critical dimensions written down so you can tell us
• File exported as STEP, 3MF or STL (see preparing files)

When You Need It Fast

Pick a collection date on the live calendar when you get your quote. Short prints, under 3–4 hours, can often be collected the same day, and larger prints usually take 1–2 days. For anything tight, message us on Telegram. If a deadline needs your job to jump the queue, a rush surcharge may apply, and it is always agreed upfront. If we can't hit the date, we'll say so before you pay. If you want to know a critical dimension came out right before you travel to collect, ask and we'll send photos and a dimension check first.

Every file gets a free check before printing. If a wall looks too thin or an orientation looks risky, we tell you and suggest a fix first. If the jig is part of a line you will need again, you can reorder it from your order page at today's price, as long as the file is still on file.

Quick FAQ

Can a printed jig replace a machined one?

Often, for light and moderate loads. For heavy clamping, high-wear surfaces or high heat, combine a printed body with metal pins and bushes, or use one of the carbon-fibre grades.

Which material should I start with?

PETG for most jigs. PA-CF if it must be stiff, and TPU for grip pads. Test a PLA version first if you are unsure of the fit and want a cheaper trial.

Can you design the jig for me?

No, we are print-only. Send us your model and we'll check it for free, flagging wall thickness, clearances, orientation and supports before it goes on a printer.

How accurate will it be?

Typically ±0.2–0.5 mm, with holes 0.1–0.2 mm undersize. Tell us the critical dimensions so we can dial them in.

Have a jig or fixture ready to go? Upload the file and see the price and collection dates now. Get an instant quote.