3D Printed Jigs or Machined Ones? Where Each Wins
3D printed jigs are fast and cheap, but ±.005" is tighter than a powder print holds as built. Print the body, put metal at the locating points, then test.
Plus or minus five thou. That was the number in an r/AskEngineers post asking which printer could make 3D printed jigs that hold it for composite parts.
Can a 3D Printed Jig Hold ±.005"?
Not reliably straight off a powder printer. Our 3D printing page quotes "±0.3 mm or ±0.3%, whichever is greater", which is about ±.012" at best and more than twice the band the poster wanted.
Replies in that thread made the same call for desktop FDM. One quoted Prusa's own figures, 0.1 mm in Z and 0.3 mm in XY, and said a CNC would likely win on accuracy and long-run cost unless the jigs were really odd shapes. Another said ±.005" almost certainly means post-machining, and that they ream holes to size.
Where 3D printed jigs earn their place
Odd shapes are exactly the point, though. A nest that cradles a curved housing is a pain to mill and easy to print. HP describes MJF fixtures it printed to hold a camera's foot assembly during bonding. In its case study, HP says machined sets could top $1,000 per set and take weeks, while the MJF parts, later versions included, were available in days.
In an r/manufacturing thread on printed fixtures, one engineer said they're typically not accurate or wear-resistant enough for production. His team debugs the design in print, then makes the production version in metal. Another said they sometimes launch with a printed fixture, keep spares, and switch to machined if it doesn't last. Both approaches hold up.
Getting the tight features right
You don't have to pick one process for the whole jig. Print the body in MJF Glass-Filled Nylon, which our materials page lists for "stiff, dimensionally stable printed parts". Then put machined dowel pins or reamed bushings where the part actually locates. Our posts on dowel pin fits and press-fit bosses in MJF cover why the metal should take the wear. If you want the pins or bushings installed for you, ask us when you quote.
If the jig takes heavy clamping loads every shift, or has to repeat between setups like a fixture plate, machine it. Our CNC page lists "ISO 2768-m standard, down to ±0.01 mm", and Aluminum 6061 is cheap insurance against a jig that creeps.
If the printed one holds up on the line, keep a spare on the shelf and let wear tell you when it's time for metal.
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