Design for Additive Manufacturing (DfAM) Guide | Chatelet Mfg
Design for Additive Manufacturing: A Practical DfAM Guide
The rules that decide whether a printed part performs in production or fails in the field — written by the people running the printers, for the engineers sending the files.
What DfAM Actually Means
Most parts that fail in FDM production weren't badly printed — they were designed for a different process. A drawing built around machining assumes isotropic material and tapped holes; a drawing built around molding assumes uniform walls and draft. Additive has its own physics: parts are built in stacked layers, which makes them directional, and geometry that costs money in machining is often free in printing.
Design for Additive Manufacturing is simply designing to that reality. Get six things right — orientation, walls, tolerances, fastening, stress geometry, and overhangs — and printed parts behave predictably in production.
1. Orientation Is a Design Decision, Not a Print Setting
The single biggest factor in printed part strength is which way the layers run relative to the load. Material within a layer is strong; the bond between layers is weaker. A bracket that survives 500 N in-plane may fail well below that if the same load pulls across layer lines.
Related: carbon fiber nylon vs aluminum covers how anisotropy factors into metal replacement decisions.
2. Wall Thickness and Feature Size
| Feature | Guidance | Why |
|---|---|---|
| Functional walls | 2 mm minimum | Below ~1.5 mm, strength becomes print-path dependent |
| Load-bearing sections | 3–4 mm+ | Sustained load needs cross-section, not infill percentage |
| Ribs | ~60–80% of adjoining wall | Thicker ribs add mass without proportional stiffness |
| Small holes | Print undersized, then drill/ream | As-printed holes trend undersized and out-of-round |
| Text / fine detail | ≥1 mm stroke, embossed > engraved | Finer detail disappears into nozzle width |
Counter-intuitive but important: infill percentage is a weak lever compared to wall count and section thickness. Doubling infill rarely rescues an undersized wall.
3. Tolerances: Design the Critical Features, Not the Whole Part
Plan around ±0.2 mm or ±0.5% (whichever is greater) on as-printed features. That's more than adequate for the large majority of brackets, housings, guides, and fixtures — and inadequate for a press-fit bearing bore, which is fine, because you don't have to print it to final size.
4. Fastening: Stop Printing Threads
Printed threads engage plastic across its weakest plane and strip after a few assembly cycles — which is exactly when a technician is servicing the part in the field. Design bosses for heat-set brass inserts instead: knurled bushings pressed in with a heated tool, giving real reusable metal threads. We install them in-house as a standard finishing operation.
Boss rules: ~2 mm of plastic around the insert, hole depth = insert length + 2 mm clearance, and a 1–2 mm fillet at the boss base. Full detail in the threaded insert design guide. Where both sides are accessible and loads are high, a through-bolt and nut is stronger still — the plastic only sees compression.
5. Stress Geometry: Fillets Are Free
Internal sharp corners concentrate stress, and in fiber-filled materials that concentration is where fatigue cracks start. A 1–2 mm fillet costs nothing to print and meaningfully improves service life. The same logic applies to abrupt section changes: taper transitions rather than stepping them.
Conversely, geometry that would be expensive to machine — organic ribbing, internal channels, consolidated multi-part assemblies — is often free in printing. DfAM isn't only about constraints; it's also about spending the freedom where it pays.
6. Overhangs, Supports, and Large Parts
Overhangs beyond roughly 45° from vertical need support material, which costs time and leaves witness marks on the supported surface. Where possible, chamfer instead of overhang, and design self-supporting angles into features like bosses and holes (a teardrop or chamfered top on a horizontal hole prints cleanly without support).
For parts exceeding a build envelope, sectioning is routine: split the part so the joint lands in a low-stress region, then join mechanically or with bonded joints. Large fixtures are frequently built this way — send the CAD and we'll propose the sectioning strategy in the quote.
7. Choose the Material Against the Environment, Not the Spec Sheet
| Requirement | Material |
|---|---|
| Outdoor / UV exposure | ASA |
| Stiff, stable, electrically insulating | Glass filled nylon |
| Maximum stiffness-to-weight | Carbon fiber nylon |
| Higher sustained heat | Polycarbonate |
| Flexible, sealing, damping | TPU |
Not sure? The manufacturing method selector will point you at a process and material family in about thirty seconds.
The Pre-RFQ Checklist
Before you send a file for quoting, confirm: primary load direction identified and stated · functional walls ≥2 mm · critical features flagged for post-machining · threaded connections designed as insert bosses · fillets at internal corners · service environment and temperature stated · annual quantity stated. Files that arrive with those seven things get accurate quotes faster — and usually cheaper, because we're not quoting around uncertainty.
Have Us Review Your Design
Send the CAD with your load case, environment, and quantity. We'll return a manufacturability review with material and design recommendations — typically within one business day, with a committed lead time.
Request a Design ReviewFrequently Asked Questions
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Chatelet Manufacturing is a US-based contract manufacturer in the Orlando, Florida area, operating 85+ FDM production printers. We produce carbon fiber nylon, glass filled nylon, ASA, polycarbonate, PETG, and TPU parts from prototype through low-volume production, with turnaround as soon as one week depending on part complexity and volume.