Design guides are full of minimum wall numbers. Under a Protolabs video comparing MJF and SLS prints, one viewer asked about the other end: is there a maximum? They wanted to know whether a 7–10 mm floor would cause uneven cooling or warping. SLS thick walls are a fair worry, and the answer is yes, there’s a practical limit.
Is there a maximum wall thickness for SLS?
Not a hard one, but bureaus start getting nervous past about 4–5 mm. Protolabs’ SLS guidelines recommend uniform walls between 1.5 and 3.8 mm. If a section goes over 4 mm, they say hollowing it to 2–4 mm walls “will be required, to avoid sink marks or even a machine crash,” and they’ll modify the CAD themselves. Xometry’s SLS design guide says there’s usually little need for walls over 5 mm.
So a 7–10 mm floor will print. It’s just the kind of feature that comes back with a dip in the middle or a corner that’s lifted.
Why do SLS thick walls cause trouble?
Heat. A big solid block holds more energy and cools slower than the thin walls next to it. Protolabs’ nylon design tips put it plainly: when one side is much thicker than the rest, the thick areas cool much slower and the part shrinks unevenly. HP’s MJF design handbook makes the same case from the other side, noting that thinner sections “accumulate and re-radiate less heat,” which helps accuracy.
What should you do instead?
Hollow it, or core it out with ribs. HP’s handbook suggests a hollow wall of at least 2 mm, with thicker walls giving better mechanical properties. Leave a drain hole if you want the powder out. If you don’t, the trapped powder stays inside. HP says that makes the part heavier, but still weaker than a solid version, and it saves depowdering time.
One catch on Protolabs’ approach: when they hollow a part, the unsintered powder inside can’t be removed. If weight matters, add your own escape holes before you send the file.
What about the floor in the original question?
Pocket the underside. A ribbed floor with walls inside the 1.5–3.8 mm range Protolabs recommends stays stiff without a big solid slab. Then match that wall thickness across the part, because a uniform section is what stops one area from cooling slower than the next.
Related on the Solvi blog: MJF Warping: Why Large Flat Parts Warp; MJF Tolerances: Clearance for Holes and Nut Pockets; MJF Threads: Print Them, Tap Them, or Use Inserts?.
Sources: YouTube: MJF vs SLS comparing prints (Protolabs), viewer question; Protolabs SLS design guidelines; Protolabs: How to design for nylon 3D printing; Xometry SLS design guide (PDF).