A viewer under Avid Product Development’s MJF walkthrough had designed an accessory in Fusion and asked what the process looks like to get it printed. The bureau’s reply was short: “All we need is a STEP or STL file. We prefer STEP files, so we can make sure you’re getting the highest quality print, with the best resolution. But STL files work too!” That’s a good starting point for the MJF file format question, and HP’s own documents explain why both work.
Which MJF file format should you send?
Send STEP if the bureau accepts it, and a well-exported STL if it doesn’t. HP’s design guidelines say its Build Manager software supports STL and 3MF. The later SmartStream 3D Build Manager user guide lists 3MF, OBJ, STL and WML (VRML), plus its own SSP format for saving a whole job.
Notice STEP isn’t on those lists. A bureau that prefers STEP converts it to a mesh itself, at a resolution it chooses. That’s the point of asking for it: you hand over exact geometry and let the shop control the tessellation.
What STL export settings does HP recommend?
If you send STL, the faceting is baked in by your CAD export. HP’s guidelines explain that angle tolerance and chord deviation define the resolution and file size of the part, and that these export parameters affect how much faceting occurs. For SolidWorks, HP recommends binary STL with a 0.05 mm deviation and a 1° angle tolerance. For Rhino, HP suggests a maximum angle of 1, a maximum aspect ratio of 6 and a minimum edge length of 0.05.
The same guide warns that STL models commonly suffer from surfaces that aren’t joined to their neighbors. HP also says job preparation may take from 15 minutes to 2 hours depending on complexity, so a clean file saves the bureau time.
What else should go with the file?
A mesh carries no tolerances, no thread callouts and no finish spec. Send a PDF drawing or a short note with critical dimensions, the material, the finish and the quantity. If a bore needs to fit a bearing, say so, because the bureau can’t tell from the triangles.
Before you upload, open your STL in a free viewer and zoom into the smallest radius. If you can see flat facets there, re-export with a tighter deviation, or just send the STEP.
Related on the Solvi blog: Netfabb MJF Job Rejected After an Update? Start Here; MJF Tolerances: Clearance for Holes and Nut Pockets; MJF Threads: Print Them, Tap Them, or Use Inserts?.
Sources: YouTube: Multi Jet Fusion (MJF) Explained (Avid Product Development), viewer question and reply; HP: Design and printing guidelines for HP Jet Fusion (4AA7-0402ENW); HP SmartStream 3D Build Manager user guide.