🧪 FDM tolerance tuning — share your numbers

[scottconverse]

Thread fit is the one thing worth a 10-minute calibration. Post your printer +
material + the clearance that gave you a clean fit, so others have a starting
point.

How clearance works

clearance is the total diametral gap between mating threads, split evenly:
an external thread shrinks clearance/2, an internal thread grows clearance/2.
Make a bolt and its nut with the same clearance and they fit.

Starting points

Fit	clearance
Tight, well-tuned	0.2 – 0.3 mm
Default / safe	0.4 mm
Loose / fast	0.5 – 0.6 mm
Coarse caps / lids	0.5 – 0.8 mm

Tips

• Print axis vertical for the cleanest flanks; no supports in tapped holes.
• Keep lead-in chamfers on (default) so threads self-start.
• profile=rounded for stronger roots on load-bearing parts.
• For v0.6 generic square/rectangular/groove forms, start with the same
  clearance table, then adjust thread_size or rect_ratio for printable
  flank thickness and strength.
• fit= records nominal ISO 965 allowance intent only. On M8 6g it is about
  0.029 mm diametral, so clearance is still the practical FDM fit lever.
• Pitch < ~0.7 mm (fine M2–M3) is at a 0.4 mm nozzle's limit — print slow or use
  a heat-set insert.

Quick calibration

Print M8 nuts at clearance 0.3 / 0.4 / 0.5 on an M8 bolt and keep the one that
spins freely without slop.

Reply with: printer · nozzle · material · layer height · the clearance
that worked. Let's build a community fit table. 📊