If you’re figuring out how to design parts for MJF, you probably care about three things: reliable, repeatable quality; tolerances that don’t surprise you after post‑processing; and unit costs that still make sense when you move from ten prototypes to a few thousand production parts. Multi Jet Fusion is forgiving compared to many processes, but it rewards disciplined CAD. This guide—aimed at U.S. product teams and manufacturers—lays out actionable, shop-proven practices you can apply immediately without drowning in jargon.

Quick refresher on MJF 

Before you start changing wall thicknesses and fillets, it helps to remember how MJF actually fuses powder. Agents are jetted where you want polymer to solidify, infrared energy does the melting, and the surrounding powder acts as a built‑in support. That freedom comes with responsibilities: thermal mass, powder evacuation, and finishing all nudge your dimensions. Understanding that interplay is what turns passable prints into production-ready parts.

How To Design Parts for MJF? Starts With Business Targets

Before any geometry decisions, align your team on the business constraints so the engineering choices you make are intentional, not reactive. This short exercise prevents you from over‑engineering prototypes or under‑engineering bridge‑to‑tooling runs. Think cost per part, lead time, and which dimensions must be post‑machined versus “print and go.”

• Define cost and schedule realities you must hit (prototype vs. pilot vs. low‑volume production).
  
• Capture functional requirements like load paths, sealing, UV exposure, and required aesthetics.
  
• Lock QA and validation up front (CMM scan, go/no-go gauges, drilling or reaming bores, dyeing, vapor smoothing).
  

Core Geometry Rules You Can Trust 

Numbers alone don’t guarantee success, but they eliminate the most common failures. The figures below reflect widely adopted practice across major U.S. service bureaus and HP guidance. Deviation is fine if you test it, document it, and keep print orientation consistent across builds.

• Walls: keep short, non‑structural walls at ≥0.8 mm; for enclosures, brackets, or load-carrying parts, use 1.2–2.0 mm.
  
• Embossed/engraved details: height or depth ≥0.4 mm with strokes ≥0.3 mm to stay legible after blasting or dyeing.
  
• Living hinges: around 0.3 mm thick and oriented in XY, not Z.
  
• Fillets: add ≥0.8 mm internal and ≥1.0 mm external to reduce stress concentration and stair‑stepping.
  
• Lattices: keep cell sizes ≥1.5 mm to ensure consistent fusion and predictable de‑powdering.

Accuracy, Shrinkage, And Realistic Tolerances

Dimensional accuracy is a function of geometry, orientation, local thermal mass, and post‑processing. Instead of promising a blanket tolerance to your stakeholders, set a primary rule of thumb and specify exceptions for CTQ features in the drawing.

• Use ±0.2 mm up to 100 mm length, then ±0.2% beyond that, as a conservative baseline for PA12.
• Expect holes to print slightly undersized; leave +0.1 to +0.2 mm for reaming or drilling.
• Model assembly allowances anywhere you plan to bead blast, dye, vapor smooth, or machine.
• Keep wall thicknesses uniform to avoid heat accumulation and warpage that drifts your tolerance stack.
  

Hollowing, Powder Escape, And Thermal Balance

Large solid blocks are the fastest route to warped parts and high material bills. Hollowing not only saves powder; it also equalizes thermal behavior, which keeps your tolerances in check. Plan escape paths like a fluid system, not an afterthought.

• Hollow thick regions and add at least two escape holes ≥6 mm on opposing faces to flush powder.
• Place escape holes high and low to use gravity and compressed air during de‑powdering.
• Keep internal channels ≥2 mm wide so powder does not cake and trap heat.
• Maintain consistent wall thickness in hollow shells, and avoid long, uneven transitions that create thermal gradients.

Strength And Stiffness Optimization (Ribs, Shells, Lattices)

Using ribs, shells, and lattices correctly lets you cut mass without compromising durability. Treat ribs as structural features that need fillets and thickness, not thin cosmetic fins. For lattices, prioritize manufacturability and de‑powdering over exotic cell patterns that look good in renderings and fail in production.

• Ribs should be 60–80% of the wall they support and filleted at the root (≥0.5 mm) to prevent crack initiation.
• Shell + lattice strategies work well: a 1–1.5 mm shell over a 15–25% gyroid/diamond core is a common, robust pattern.
• Bosses for inserts need extra meat: follow the heat‑set insert vendor’s pilot and wall thickness recommendations to avoid cracking.

Designing Assemblies And Moving Parts

Printing assemblies in one shot is tempting, but fused joints are expensive to reprint. When you do it, give every contact surface enough air to survive the thermal cycle and the breakout process. Validate a single sample set before committing to production volumes.

• Leave 0.25 mm clearance per side between moving surfaces to prevent fusion.
• Orient parts to minimize long, parallel close faces that can sinter together.
• For snap fits, model +0.15 mm clearance per side and confirm stiffness with real prints, not solely FEA.
  

Surface Finish And Post‑processing

MJF parts come off the machine with a matte gray finish and a typical Ra around 6–8 µm. Every finishing step alters geometry slightly, so build clearances and tolerances around what you will actually apply, not what you wish you could skip.

• Bead blasting even texture, but can remove a few hundredths of a millimeter—budget for it on tight fits.
  
• Dyeing (often black) penetrates roughly a quarter millimeter, so don’t rely on it to mask loose clearances; design them in.
  
• Vapor smoothing improves surface integrity and watertightness; add 0.05–0.15 mm extra clearance on critical interfaces.
  
• Secondary machining (drill, ream, tap, face) is often the cheapest way to guarantee CTQ dimensions.
  

Quality Assurance And Documentation For Repeatability

Repeatable MJF production depends on documenting more than just nominal dimensions. Capture how you nested, oriented, and finished each part, then lock that into your drawings, traveler, or MSA files. The more regulated the application, the more this matters.

• Freeze build orientation and packing density for production runs; keep annotated screenshots in your release package.
  
• List CTQ dimensions and gauges (CMM, structured light scans, or go/no‑go) to avoid ambiguous inspection.
  
• Track material lot numbers and post‑processing recipes when regulatory or medical compliance is involved.
  
• Record annealing or smoothing parameters (time, temperature, chemistry) to ensure lot‑to‑lot consistency.

Common MJF Design Mistakes And Quick Fixes

Teams often repeat the same preventable errors: thick solid masses that warp, razor‑sharp inside corners that crack, undersized bores that never get reamed, and assemblies with near‑zero clearances that fuse into expensive paperweights. Fixing these requires simple, codified rules in your CAD checklist.

• Don’t model solid bricks—hollow thick zones, add vents, and keep walls uniform.
  
• Fillet every inside corner that sees load or heat concentration.
  
• Assume holes print tight and plan to ream or drill.
  
• Give moving parts breathing room—treat 0.25 mm per side as your default starting point.
  
• Normalize wall thicknesses and use ribs for stiffness, not random thickness spikes.
  

Material Choices For MJF 

PA12 is the default, but it’s not the only option. Material decisions influence strength, ductility, chemical resistance, color, and even surface finish. Select intentionally, then adapt your design rules (wall thickness, clearances, post‑processing) to match the chosen polymer.

• PA12: balanced strength, stiffness, and accuracy; ideal general‑purpose production.
  
• PA11: higher toughness and impact resistance; good for snap‑fits and living hinges.
  
• Glass‑ or mineral‑filled nylons: higher stiffness and temperature resistance, but more brittle—add generous radii.
  
• ESD‑safe grades: for electronics housings; confirm surface resistivity ranges with your supplier and test parts, not just coupons.

DFM Checklist To Run Before You Upload The CAD 

A short, enforced checklist prevents 90% of reprints. Run it internally before you send files to your bureau, and ask your vendor to confirm it on their side. This is the cheapest quality control you’ll ever implement.

• Are all walls ≥0.8 mm, with load-bearing or tall walls at 1.2–2.0 mm?
• Did you hollow thick regions and add ≥6 mm escape holes on opposing faces?
• Did you allocate +0.1–0.2 mm for any holes that need tight tolerances post‑print?
• Are moving parts spaced ≥0.25 mm per side, and are snap fits given +0.15 mm?
• Have you documented orientation, packing density, and post‑processing steps needed for production?
  

Conclusion

Great outcomes come from designing with the physics of the process—heat, powder flow, and finishing—in mind. Balance your walls, create real powder escape paths, budget for machining where it saves headaches, and document orientation so every batch behaves the same. Do that, and you’ll control quality, slash rework, and keep unit costs predictable as you scale from prototype to production in the USA. If you want a fast DFM pass or a second set of eyes on your next build, Elite Mold is ready to review your CAD and suggest the most economical way forward.

FAQs

Is there a single minimum wall thickness I can always rely on?

0.8 mm is a widely used safe minimum for short, non‑structural walls. If the feature is tall, load‑bearing, or sees heat, increase to 1.2–2.0 mm.

Can threads be printed directly?

Yes, for larger sizes (M6 and up), but for durability and repeatability, most teams print a pilot hole and use heat‑set inserts or post‑tapping.

How accurate will flat sealing faces be out of the machine?

Plan ±0.2 mm and use vapor smoothing or machining if you need tight sealing.

Will vapor smoothing change my dimensions?

Slightly. Add 0.05–0.15 mm clearance to interfaces where precision matters.