Under Formlabs Support’s video on reading the Fuse tuning print, one viewer asked the obvious question. Why does the guide call the part with defects normal and the flawless one overheated? Anyone who’s tuned FDM or SLA expects the cleanest part to win. SLS bed temperature tuning doesn’t work that way.
Why is the plaque with defects the right one?
Because the test is built to make the right offset visible, not to make good parts. Formlabs Support replied that the “poor” result being ideal is “really counter intuitive,” but the plaques are designed for that specific print and “it does not reflect the quality of parts going forward.” It’s an indicator, nothing more.
The commenter pushed back with a fair point from other processes: more heat fuses better but adds defects, so you hunt for the middle. That’s roughly what the plaques do. They just make the middle easy to see.
What are you actually looking for?
Two things, per Formlabs’ tuning guide for Nylon 12. You want more than one but fewer than six spots of orange peel on a plaque, which shows on the cones. And you want no pitting, the tiny dots on the flat side opposite the cones. The five cone plaques are printed at −2, −1, 0, +1 and +2 °C. Line them up in order and the answer usually falls between two of them, so a +1.5 °C setting is fine.
Ignore the flat filler plaques. They’re only there to even out cooling in the build and can go in the bin.
How do you run it without fooling yourself?
Use aged powder refreshed with 30% fresh, which is what Formlabs specifies. If all you’ve got is new powder, age a batch first. Load 3 kg, which fills the hopper to the 7 L mark. On recent firmware, the printer also reports exhaust status after the test. If it says Dirty, clean the filter, fan and tube and rerun the print, because Formlabs says the first set of plaques isn’t valid.
Then set the offset under Settings, Calibration, Bed Temperature Target. It moves in 0.25 °C steps up to ±5 °C, and only while the printer is idle.
Does SLS bed temperature tuning carry over between printers?
No. Formlabs notes that two printers side by side can need different offsets, so don’t copy one machine’s number to the next. Write each printer’s offset on a label on its front panel along with the date and powder lot you tuned with.
Related on the Solvi blog: SLS Orange Peel: Why It Happens and How to Fix It; SLS Cooldown: How Hot Can You Unpack a Build?.
Sources: YouTube: How to read the bed temperature tuning test print (Formlabs Support); Formlabs: Tuning the bed temperature with Nylon 12 Powder; Formlabs: Evaluating diagnostic print results.