These use a rotating drum with one or more hardened blades, cutting onto an anvil(s) mounted in the throat of the feed.

The drum may be parallel sided or waisted in the middle.

The feed mechanisms are similar to those of disk chippers or may use a conveyor or gravity.  A separate fan may be incorporated, or the blades themselves may generate the airflow to blow the chips out.

Chip size is determined by drum speed, feed speed and the number of blades.

The axis of the drum is at right angles to the direction of feed, and the whole width can be used.  If material can twist in the throat during infeed it can result in long slivers.  One design uses a drum that is tapered to the centre, partly to try to minimise this. 

High quality chips can be achieved with some designs, particularly in combination with a screen.

Drum chippers are flexible in being able to handle a range of different material, including twiggy material and roundwood.

As with disk chippers, blades are replaceable and can generally be resharpened.

Blades can be blunted or damaged by dirt, stones inclusions or ice, and in high throughput situations can require sharpening or replacing up to several times a day. Blunt blades can lead to irregular chip sizes, more slivers and greater power requirements.  It is highly advisable to ensure a supply of spare blades so that they can quickly be replaced as required and sharpened at convenience.