These operate on a different principle to disk and drum chippers.

The cutting blade is a rotating, tapered, helical screw thread with a hardened cutting edge, which cuts against the inside of the housing.  The axis of rotation is in line with the direction of feed and the helix draws material into the chipper and is the only feed mechanism required.

Chip size is determined by the pitch of the screw, and can be varied by replacing the blade with one of a different pitch. 

The base of the blade generally includes a disk to generate the airflow to propel the chips out, and may also incorporate a sliver breaker.

As material is drawn into the chipper by the action of the screw a separate mechanical feed system is not usually employed.

Screw chippers can produce high quality, even sized chips, with good throughput. However they typically require high drive powers.

Owing to the feed mechanism it is very difficult to withdraw material once it has started to be drawn in.

Screw chippers tend to be more quiet in operation than other types.

As with all chippers it is important to ensure that the blade remains sharp, especially if high quality chips are required.

The entire helical blade can be replaced, or can be sharpened in situ using a jig provided by the manufacturer.  The hardened face can be reconditioned by welding and grinding.