Under Protolabs’ video comparing SLS and MJF finishes, a viewer asked whether the standard finish comes from shot blasting after unpacking, or whether it’s just the surface left once the powder is brushed away. The answer depends on whose “standard” you mean, and that’s the trouble with the phrase MJF standard finish.
Is the MJF standard finish bead blasted?
At Protolabs, yes. Its MJF page says a bead blast removes all powder and leaves a consistent overall texture, and then parts are dyed a standard black. Its as-printed option comes out gray and slightly rougher. So “standard” there means two steps past the printer, blasted and dyed.
What happens before the blast?
Protolabs lays out the sequence. The whole powder bed moves to a processing station, where an integrated vacuum pulls off most of the loose powder. Bead blasting removes what’s left before parts go to finishing for dye. Vacuuming gets the bulk off, but it’s the blast that Protolabs credits with the even texture.
Can blasting hurt a part?
Thin ones, yes. HP’s MJF design handbook warns that if walls are too thin, the part won’t survive cleaning and sandblasting. It also treats threads as very fine detail and recommends glass bead media of 70 to 110 microns at 3 to 4 bar, since vibratory finishing media are usually too big to clean between threads.
Tumbling is the riskier step for snap-fits. HP says it can reduce the mating force or even break the fit, and suggests protecting those parts in a sinter box.
How should you write it on a quote?
Spell it out. “Standard” means blasted and dyed at Protolabs, and it could mean vacuum-only somewhere else. List each step on the quote: depowdered, bead blasted, then dyed black or left natural gray. If a customer’s drawing just says “standard finish,” ask which bureau they’ve ordered from before, and send a blasted sample with the first article.
Related on the Solvi blog: Should You Dye MJF Parts Black or Vapor Smooth Them?; SLS Bead Blasting: What Causes Residue on Parts?; MJF Threads: Print Them, Tap Them, or Use Inserts?.
Sources: YouTube: SLS and Multi Jet Fusion finishes compared (Protolabs), viewer question; Protolabs: Multi Jet Fusion 3D printing service; Protolabs: 3D printing finishing options; HP MJF Design Handbook (PDF).