MJF tolerances come up as soon as a customer designs printed parts that take hardware. In an April 2026 r/3Dprinting thread, a designer planning MJF PA12 parts asked what clearance to give openings for M5 and M6 nuts. The answers show why a bureau needs a clear, consistent reply.
What did operators say?
Answers ranged from “nominal or 0.1 mm over” to “make the hole 0.2 mm bigger to be sure” when ordering from a service provider. One commenter said it can vary from 0.1 to 0.3 mm and that internal pockets usually come out a little undersized. (That commenter also attributed a ±0.3 mm figure to HP; the HP documents cited below don’t state that figure, so treat it as unconfirmed.) Another pointed out that it depends on part orientation and how dense the build is.
What does HP publish on MJF tolerances?
HP’s MJF Handbook (“Design for accuracy”) says MJF can reach accuracy values of IT Grade 13. It lists a minimum hole diameter of 0.5 mm at 1 mm thickness and a minimum clearance of 0.5 mm at 1 mm thickness. For parts printed separately that must fit together, HP’s handbook recommends a gap of at least 0.4 mm between mating surfaces, allowing ±0.2 mm of tolerance on each part. Parts printed together as an assembly should have at least 0.7 mm of clearance, per the same handbook. HP’s PA 12 data sheet doesn’t give a numeric tolerance, so quote tolerances as typical values, not guarantees, and agree on critical dimensions with the customer up front.
Why do holes come out undersized?
JLC3DP explains that circular features tend to print slightly small as the surrounding powder restricts the nylon while it cools and contracts. The effect is stronger for small, deep and Z-oriented holes. Bosses hold heat longer and can go oval or sink at the base.
Why can’t the printer just scale it out?
Bureaus set global scaling factors per machine and material, but RapidMade notes these correct the average shrinkage of the build. Features with unusual thermal mass, very thick or very thin, can still drift. On large parts, a small shrinkage error becomes a bigger absolute deviation.
What should a bureau tell customers?
- Publish a default clearance for nut pockets and holes, and say it depends on orientation.
- Ask which dimensions are critical, and orient those features accordingly.
- For press fits, remember that surface texture becomes part of the tolerance stack.
- Recommend a test print or reaming for anything tighter than your standard.
How do you keep answers consistent?
Write your standard clearances and tolerance statement down once and put them on your quote page and DFM notes. Track fit complaints by feature type so you can adjust the guidance based on your own machines.
Related on the Solvi blog: MJF Threads: Print Them, Tap Them, or Use Inserts?; MJF Warping: Why Large Flat Parts Warp.
Sources: r/3Dprinting MJF tolerances thread; HP MJF Handbook, Design for accuracy (4AA7-4107ENW); HP MJF Design Handbook (incl. Best practices, 4AA7-4072ENW); JLC3DP MJF tolerances guide; RapidMade MJF as-printed tolerances analysis.