Bolt torque reference
Summary¶
Every fastener in the libdrone frame has a specified torque. Under-torquing allows micro-movement that loosens joints and transmits vibration. Over-torquing crushes printed material, strips threads, or pre-stresses parts past their design limit. The most dangerous fastener in the build is the M3 sandwich bolt — it holds the entire five-layer body together, and over-torquing it cracks PCCF layers. This article is the single reference for all libdrone fastener torques. Consult it during initial assembly and whenever any bolt is touched during maintenance.
Concept¶
Why printed materials need lower torques than metal¶
A bolt torqued into metal compresses a stiff, elastic material — the compression stores energy and maintains clamping force indefinitely. A bolt torqued into a printed PETG or PCCF bore compresses a viscoelastic material that creeps slowly under sustained load. This means:
- Over-torquing produces immediate cracking — the printed walls around the hole cannot sustain the hoop stress.
- Even correct torques experience some relaxation over time — check and re-torque at the maintenance intervals in → scheduled-maintenance.
- Loctite 243 (medium strength) on fasteners into printed plastic compensates for relaxation without preventing future removal.
The torques below assume standard M2/M3/M5 steel bolts into printed PETG or PCCF without threaded inserts, unless otherwise noted.
Reference¶
Master fastener torque table¶
| Fastener | Location | Torque | Notes |
|---|---|---|---|
| M5 prop nut | Motor shaft | Snug + ¼ turn | Tighten in motor spin direction; do not over-torque shaft |
| M3 motor screws | Into passive cover + nyloc nut | 0.4–0.5 N·m | See → floating-motor-mounts |
| M3 sandwich bolts | Through all 5 X body layers | 0.3 N·m | Do NOT exceed — crushes PCCF |
| M3 pinch slit bolt | Arm rod clamp | Gradual tighten until rod play gone | Check acoustic ping after — see → pre-tensioning |
| M3 GPS mast screws | Into backplane boss pads | 0.3 N·m | |
| M3 payload mast screws | Into platform boss pads | 0.3 N·m | Finger-tight + ¼ turn acceptable |
| M3 GX12 chimney lock | Connector lock ring | Finger-tight only | Screw-lock — do not use tools |
| M2 shaft-to-tab screws | Arm shaft onto tabs | Finger-tight + ¼ turn | 4 screws per arm; do not crush PETG |
| M2 active/passive cover screws | Arm covers | Finger-tight + ⅛ turn | These are short — strip easily |
Loctite application¶
Apply Loctite 243 to all fasteners that thread into printed plastic: M3 sandwich bolts, M2 shaft-to-tab screws, M3 pinch slit bolts. Do not apply to M5 prop nuts (must be removable for prop changes) or GX12 lock rings (field-removable connectors).
Allow 20 minutes cure before applying torque. Full cure: 24 hours.
Re-torque schedule¶
| Fastener group | First re-torque | Subsequent interval |
|---|---|---|
| Sandwich M3 | After first 5 flights | Every 20 flights |
| Motor M3 | After first 5 flights | Every 10 flights |
| Shaft-to-tab M2 | After first crash | Every 20 flights or any crash |
| Pinch slit M3 | After acoustic ping failure | As needed |
Procedure¶
Torque sandwich bolts correctly¶
- Thread all 6 sandwich bolts finger-tight first — do not torque any individual bolt fully before the others are started.
- Tighten in diagonal pairs to distribute compression evenly: 2 opposing corners → opposite 2 corners → front/rear pair.
- Stop at 0.3 N·m on a torque driver. If a bolt feels significantly looser than the others at this torque, the threaded hole may be stripped — inspect before proceeding.
- Verify no PCCF cracking visible at bolt holes under magnification.
Check pinch slit torque¶
The pinch slit bolt has no fixed torque because it is set by feel: tighten gradually, checking rod play after each quarter-turn. Rod play is confirmed gone when the rod cannot rotate under 0.5 N·m applied by hand. Do not continue past this point — further torque crushes the slit walls. Verify with acoustic ping: → pre-tensioning.
Rationale¶
A consolidated torque reference was created because fastener torques were previously scattered across DMOM §2.5.1, the arm-shaft atom Procedure section, and the floating-motor-mounts Reference section. A builder assembling the frame from scratch needed to consult three documents for complete torque coverage. A single lookup table eliminates the risk of missed fasteners and gives workshop participants a printable reference card for the build session.
Connections¶
requires: - frame-structure-overview related: - arm-shaft - floating-motor-mounts - sandwich-structure - pre-tensioning - scheduled-maintenance - corrective-maintenance leads_to: - pre-tensioning - scheduled-maintenance