MJF design guidelines
Design limits, tolerances, and file requirements for PA12 parts printed on HP Multi Jet Fusion.
25 mm prints at ±0.25 mm
- ISO 286 grade it fits (HP's method)
- IT13
- Same size, other axis
- ±0.42 mm
- Same size, Cpk 1.00
- ±0.19 mm
- Dimensions inside the band
- 99.9937%
| Nominal | XY · Cpk 1.33 | Z · Cpk 1.33 | XY · Cpk 1.00 | Z · Cpk 1.00 |
|---|---|---|---|---|
| 0–30 mm | ±0.25 | ±0.42 | ±0.19 | ±0.34 |
| 30–50 mm | ±0.30 | ±0.50 | ±0.23 | ±0.40 |
| 50–80 mm | ±0.37 | ±0.60 | ±0.28 | ±0.47 |
Source: HP white paper 4AA7-7138EEW (2022), Tables 2, 3 and 6. HP Jet Fusion 5200, HP 3D HR PA 12 at a 20% refresh ratio, Balanced print profile, natural cooling, general dimensional profile, measured after standard surface finishing. The ISO 286 grade follows HP's own method (Figure 5): the ± value against the full IT width, which is how HP arrives at IT13 in XY and IT14 in Z. HP notes results may vary with other jobs and geometries. A size exactly on a band edge (30 or 50 mm) takes the looser band. Cpk 1.33 is the level HP calls desired for manufacturing; Cpk 1.00 is a looser statistical target. ISO 286 widths from the same white paper (Table 7); the ±0.05 mm machining figure and pre-hole rules from HP's MJF Handbook.
Add results to keep them in one document.
MJF minimum features and design rules
| Rule | Value | Note |
|---|---|---|
| Walls and features | ||
| Minimum wall, short walls in XY | 0.3 mm | HP's figure is for short walls |
| Minimum wall, short walls in Z | 0.5 mm | |
| Minimum wall in general | 1 mm | Materialise's figure, without HP's short-wall caveat. Large parts may need thicker walls, ribs or fillets |
| Flat plane that usually deforms | 210 × 297 mm | Materialise: a flat plane the size of an A4 page. Support ribs under it make it worse, and HP also advises against ribs on large flat areas |
| Wall of a hollowed part | 2 mm | Thicker walls give higher strength. Add drain holes to remove powder; powder left inside makes the part heavier and stronger than fully hollow, but weaker than solid |
| Section worth hollowing, from | 20 mm | Materialise: hollow out walls thicker than 20 mm. HP: a thinner section holds and re-radiates less heat |
| Recommended shell of a hollowed part | 2–3 mm | Materialise |
| Drain holes for powder removal | 2 × Ø2 mm | Materialise's minimum, in count and diameter. HP notes drain holes can also be added after printing |
| Internal channel Ø, to clear powder | ≥ 3 mm | Materialise. A strip or chain designed through a long channel helps dislodge the powder |
| Gap between lattice beams | ≥ 1 mm | Materialise: lets unfused powder out |
| Minimum feature width | 0.1 mm | |
| Minimum slit between walls or embossed details | 0.5 mm | |
| Cantilever narrower than 1 mm | L/W < 1 | Keep it shorter than it is wide. HP gives no rule from 1 mm up; for high aspect ratios, thicken the wall or add ribs or fillets |
| Length-to-width ratio before warpage risk | 10 : 1 | Also watch abrupt section changes and thin curved shapes |
| Layer thickness | 0.08 mm | Z dimensions resolve in these steps |
| Holes and pins | ||
| Minimum hole Ø, through 1 mm of wall | 0.5 mm | |
| Minimum shaft Ø, 10 mm tall | 0.5 mm | |
| Minimum clearance, 1 mm thick | 0.5 mm | |
| Optional pre-hole for an interpolated hole or bearing seat, under the final Ø by | ≥ 1 mm | If a drill of the final size will be used, leave the hole out and let the CNC drill it |
| Standard machining tolerance | ±0.05 mm | What HP quotes for machining after printing |
| Gaps and assemblies | ||
| Gap between connecting parts | 0.4 mm | ±0.2 mm per part |
| Clearance between moving faces, printed assembled | 0.7 mm | More for walls of 30 mm or thicker |
| Clearance, printed assembled, walls under 3 mm | 0.3 mm | Design-dependent; test before production |
| Chains printed in one piece | n·l − (n−1)·2t | Printed length, with n links of length l and thickness t. Subtract 2t more if the end links attach to something. Print links at ±45° to the bed |
| Printed hinges | Pin + middle knuckle as one | Only the outer knuckles turn around the pin, so the hinge wobbles less |
| Living hinge wall | 0.5 mm | Materialise's minimum; HP publishes none. Walls that are too thin won't survive cleaning, and a 0.1 mm change in thickness changes flexibility a lot |
| Living hinge length, thin walls | 10 / 25 mm | Materialise: 10 mm attached at one end, 25 mm attached on two sides. Neither guide gives a limit for thicker hinge walls |
| Living hinge orientation | Thin plane in XY | HP: print thin planes roughly parallel to XY. Materialise: keep the thinnest section out of the Z plane. Round the fold so it doesn't snap |
| Text and surface | ||
| Embossed or engraved text, height or depth | 1 mm | |
| Minimum font size | 6 pt | Embossed or debossed |
| Upward-facing flat areas, angle to the XY plane | > 20° | Hides layer steps |
| Downward-facing surfaces, avoid angles under | 5–10° | |
| Joints | ||
| Printed threads | > 6 mm / ¼ in | M6 or ¼ in and smaller: we install a heat-set insert |
| Custom thread gap | 0.2–0.4 mm | Plus a 0.1 mm minimum edge radius on custom threads |
| Snap-fit base thickness | ≥ 1 mm | |
| Snap-fit overhang depth | ≥ 1 mm | |
| Snap-fit assembly angle | 35–40° | |
| Snap-fit force | 50–100 N | Ergonomic ceiling for finger force |
| Heat-set insert hole, depth and boss | Insert calculator | Sized per insert in the threaded-inserts guide |
| Adhesive joints, thickness threshold | 1.7 mm | Under it: dovetail or offset overlap. Over it: overlap with jigsaw features |
Source: HP Multi Jet Fusion Handbook (2019): Design guidelines, Union joints and Innovative designs chapters, and Materialise, Design guidelines for PA 12 (MJF), where the row says so. Values are general recommendations for PA12; part geometry can change the result. The heat-set insert rule for M6 and smaller is ours.
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