Short answer
A drum cutter is a hydraulic attachment fitted to the stick of an excavator that mills rock, concrete and hard ground away from the surface with the picks on its rotating drums. It applies no impact to the material; as the picks turn they shave thin chips off the surface, and excavation advances as those chips accumulate. On a transverse drum cutter the drums turn on an axis perpendicular to the stick, so the attachment enters the ground along a narrow, deep line. It is used for rock excavation where blasting is not available, for work where a specified profile has to come out cleanly, and for taking out concrete or rock where vibration is restricted.
What a drum cutter is and how it works
The heart of the attachment is a hydraulic motor. Oil flow from the carrier turns the motor, and the motor turns the drums through a drive. Pick holders are welded to the body of the drums, and the picks sit in those holders. The working part of a pick is a hard metal conical tip, and that tip does the actual cutting.
As the drum turns, each pick comes to the surface in its turn, penetrates the material with its point and lifts off the thin slice in front of it. Instead of starting a crack by impact as a breaker does, it cuts the material. Each pick takes only its own share; the speed of excavation comes from the number of picks, the drum speed and the thickness of the layer taken per revolution together.
On the transverse design two drums turn in opposite directions on a common axis perpendicular to the stick. The cut material is thrown back between the two drums, which keeps the cutting zone clear. That geometry lets the attachment enter the ground along a line, and it is why the transverse type is strong in narrow, deep sections, in trenching and in profile work.
Depth of cut and rate of advance are managed by the operator. The boom and stick press the drum against the face, and the rate of advance is kept in step with the cutting rhythm of the drum itself. At the right rhythm the drum holds its speed and the sound stays even; push past it and the speed drops, so the picks stop cutting and start rubbing.
The pick must be free to rotate in its holder
Picks sit tightly in their holders but are not locked: while working they turn slowly about their own axis, and that rotation is what wears them evenly all round and keeps them sharp. A pick seized in its holder wears flat on one side, stops cutting, starts rubbing and quickly destroys both itself and its holder. The first thing to check on a pick is not how worn it is but whether it still turns freely.
Where it is used
A drum cutter is the attachment for work where what matters is less how fast the excavation goes than what surface it leaves behind. That is the common thread across all of its applications.
- Tunnels and underground works: bringing the section to the design profile after excavation, and surface preparation.
- Blast free rock excavation: the excavation itself on sites where blasting is prohibited, permit bound or too risky.
- Trenching: opening a narrow line in rock with straight walls and an even invert.
- Removing layers from concrete: stripping deteriorated cover from bridge decks, retaining wall faces and industrial slabs.
- Profiling slopes, walls and trench edges.
- Frozen and stiff clay ground: materials where impact cannot propagate a crack and a breaker tool simply buries itself.
- Restoration and selective demolition: taking out only the failed layer without disturbing the sound section.
What problem it removes on site
The first problem a drum cutter removes is vibration. With no impact, no impact vibration reaches neighbouring structures, existing support or buried services. On a site with neighbours that means excavation becomes permissible at all; the method itself lifts the constraint.
The second is overbreak. Once an impact tool starts a crack, you do not decide where that crack stops, and every break beyond the profile has to be filled later. Milling can stop on the target line. The surface comes out as specified, and the repair and extra fill step drops off the programme.
The third is the materials where impact simply does not work. Clay, frozen ground and formations that behave plastically do not propagate cracks; a breaker tool buries itself and the energy is wasted. A drum cutter cuts this material away, which does not solve the problem so much as change what the problem is.
The fourth is the excavated material itself. Because milled output is fine and relatively uniform, loading and haulage become easier, and where the specification allows it can go to fill without a further sizing step.
The cost logic: where the saving comes from
The economics of a drum cutter are not measured in rate of advance. In a comparison that looks at volume removed per hour, a breaker is usually ahead; what a cutter earns sits in the items where speed is never the question.
The saving comes from three places. The first is work not done: an excavation that does not run past the profile is a void that will not need filling later. The second is work not stopped: hours lost to vibration and noise limits, permits not granted and complaints from neighbours all stretch the programme directly. The third is being able to use the excavated material on site.
The other side of the sum is equally plain. The main variable in running cost is pick consumption, and how abrasive the material is drives that consumption more than anything else; in hard, abrasive rock it is the item that most often upsets the calculation. To that add the cost of the attachment, the working hours of the carrier and the downtime set aside for changing picks.
Which way those two sides tip on a given project, where a breaker stays ahead and how to frame the decision question are covered in a separate article.
Day to day operation and maintenance
Maintaining a drum cutter revolves largely around the picks and the oil flow. It is not a complex attachment, but neglect shows up quickly both in output and in consumable cost.
- Pick round at the start of shift: find and replace missing, broken and seized picks. When one pick is lost, the picks beside it have to take its share as well and chain wear begins.
- Changing picks: they are removed and fitted one at a time and the job is done on site. A pick left too long wears its holder as well, and from that point the repair becomes a welding job.
- Water spray: dust suppression helps both the surroundings and the cooling of the picks. A cutting zone the water does not reach runs dusty and hot.
- Motor case drain line: leakage oil from the hydraulic motor has to return straight to tank. Back pressure in that line strains the motor seal, so verify the connection at installation.
- Warm up in cold weather: turn the drum unloaded and let the system reach temperature before going under load.
- Parking: never rest the attachment on its picks. Set it down on firm, level ground so that the body takes the weight.
- Sound and speed: a drum running properly has an even note. Drum speed falling as you push harder is the most reliable sign that the advance has outrun the cutting rhythm of the drum.
Which carrier it fits: getting the match right
A drum cutter and a hydraulic breaker do not ask the same thing of a carrier, and that difference sits at the centre of the match. A breaker does its work largely through pressure; a drum cutter works on flow.
Flow translates into drum speed. If the attachment line of the carrier cannot deliver the flow required, the drum turns slowly, the picks rub instead of cutting and progress collapses. Too much flow overspeeds the motor. Pressure, in turn, sets the torque: without enough pressure the drum stalls under load. Both have to be met together, and both are verified against the hydraulic data of your own machine.
Weight class is the second heading. The attachment is carried at the end of the stick, and the work is often done away from the machine with the boom out. The calculation therefore follows not just the attachment weight but the reach in use and machine stability at that reach.
The third is the line arrangement. Alongside the feed and return lines the attachment needs a separate motor case drain; the return should pass through a filter and the line should not be choked. If working in both directions is wanted, the reversing arrangement is planned at installation.
To see how these headings work out on your own machine, enter the class of your carrier into our selector tool; the compatible drum cutter classes are listed there.