# Couplers and threadlocker

The motor shafts, the gearbox outputs and the joint 6 shaft are joined by couplers and pulleys with set screws on
flats or keys. Vibration loosens set screws; a loose one lets the motor turn without the joint, and the robot
loses its position without noticing.

- If a joint starts to slip, or its position drifts between homings, find the set screw, tighten it, and apply
  **blue (medium) threadlocker**. Do not move the robot for 24 hours while it cures.
- Put a screw on the key as well as on the flat where the part has both.
- Apply threadlocker to every metal-to-metal screw joint on the robot: the motor mounts, the gearbox flanges,
  the bearing clamps. Printed parts and brass inserts do not need it, and the solvent in some threadlockers
  attacks plastic: keep it on the metal.
- Never use red (permanent) threadlocker; the parts cannot be taken apart again without heat.

After tightening a coupler, home the robot and check the witness marks.