Does a Printed Nylon Bearing Surface Need a Bushing, or Can It Run Against Bare Nylon?

It depends on cycle count and load, but the honest default is: if the joint sees continuous motion or real load over the part's life, put in a bushing. Bare printed nylon running against a metal shaft or another nylon surface works fine for light, occasional motion, and wears unacceptably fast under sustained load or high cycle counts.

Why bare nylon falls short

Printed nylon, MJF or SLS, both of which DigiForge runs, has a build texture that's rougher than machined or injection-molded nylon straight off the printer, even before considering wear. That texture acts like a mild abrasive against a mating surface for the first several hundred cycles, and the printed part itself doesn't have the crystalline consistency of an extruded or machined nylon bushing built specifically for wear resistance. Under light, intermittent motion, a latch, an occasional adjustment knob, that's a non-issue. Under continuous rotation or reciprocating motion, the bore wears oversized, and once it's oversized the geometry that was providing alignment starts to wander, which accelerates wear further.

What actually determines the decision

• Cycle count. A handful of cycles per day for the product's life is a very different problem than continuous rotation. Low cycle counts can often run bare nylon indefinitely; high cycle counts wear the bore into a loose fit within a fraction of the intended service life.
• Load. Light axial or radial load spreads across the bearing surface without much local stress. Heavier load concentrates force on fewer contact points on the as-printed texture, which wears those points preferentially and can lead to an oval bore rather than a clean round one.
• Precision requirement. If the joint just needs to rotate freely, bare nylon wearing in slightly isn't a functional problem. If the joint needs to hold a consistent running clearance for alignment or noise reasons, that same wear is a failure.
• Shaft material and finish. A rough or unfinished metal shaft accelerates wear on the nylon bore regardless of load; a ground or polished shaft is gentler on the mating surface.

The bushing option

A press-fit or bonded-in bronze or Delrin bushing gives the bore a wear surface that isn't the printed part itself. It's a design change, not a process change; the printed part's bore is sized to accept the bushing rather than to run directly against the shaft. This is the more reliable path any time the joint is load-bearing and cycles regularly, because it puts the wear on a component designed for it instead of on the print.

The practical takeaway

Bare nylon-on-nylon or nylon-on-metal is fine for light, occasional motion. The moment the joint is doing real work — continuous rotation, meaningful load, or a tight clearance that has to hold over the product's life — design in a bushing rather than counting on the as-printed surface to hold up.