Diagnosis: Worn chuck jaws or an incorrect/damaged bit shank. Follow this sequence.
- Inspect the bit. The shank must be clean, round, and undamaged. A deformed or dirty shank cannot be gripped.
- Clean the chuck. Use compressed air to blow out metal dust or debris from the chuck jaws.
- Secure the workpiece. Use clamps or a vise. Holding the work by hand makes it unstable and can cause loss of control, which may feel like the bit is falling out.
If that didn't work, the chuck mechanism is faulty. Before any repair, disconnect the battery pack. The chuck is not a user-serviceable part. Have your power tool serviced by a qualified repair person. Do not use the tool if the chuck cannot secure a bit; loss of control can cause personal injury.
Heads up: Always hold the tool firmly with two hands when drilling—one on the handle, one gripping the bottom around the battery area. Use the auxiliary handle if provided.