Compression routers in woodworking offer a superior cut – reducing waste and improve cutting finish

Designed to compresses the wood chips towards the centre of the tool, compression routers:

  • Reduce chipping
  • Can be used to cut many sheets of board at the same time
  • Or cut multiple profiles from one sheet

Simon Richardson ANCA Product Manager gives some insight into the use and applications for solid carbide Compression Routers (also known as compound shear cutters) used in the woodworking industry. 

Compression Routers (CR) are used for machining composite materials and extensively in the woodworking industry to cut solid wood and particle boards. CR for woodworking applications are distinct from other types of shank tools as they have opposing flutes and can have both right and left helix cutting edges. Available in roughing (with chip breakers) and for finishing operations CR are also produced in a range of single flute and multiple flute tools.

ANCA’s compression router (Image credit: ANCA)

ANCA’s ToolRoom Software has a dedicated package to produce all types of Compression Routers with the required geometry. In addition, the digitising routines within the software exactly follow the geometry which means regrinding Compression Routers is easy.

Benefits of Compression Routers

Compression Routers are used for machining wood, flat pack furniture, kitchen cabinets and worktops. Materials such as plywood and melamine board have a finished face on the top and bottom of the material. When the board is cut, “break out” or chipping of the material on either side of the board can occur and looks unsightly. Severe break out or chipping after cutting can mean the part is scrapped or further finishing or sanding work is required.

Simon Richardson goes onto to say “the benefit of a compression router is when it cuts the material the tool “compresses” the chips towards the centre of the tool. The “Upcut” part of the router forces chips upwards while the “Downcut” section forces chips downwards towards the tip of the tool.

Cutting Tool Manufacturers know when grinding a CR, it can be a challenge to maintain size consistently between the up and down cut diameters.  For these types of tools, fluting can be a contributor to diameter variance. ANCA’s LaserPlus system now supports measurement and compensation of Compression Routers. It is now possible to measure both up and down cut diameters or single sections of the router using the Laser. This capability is invaluable for companies producing these tools as consistency will be maintained between the cutting diameters.

CR are used on CNC Gantry Routers or 5 to 3 Axis machining centres for cutting many sheets of board at the same time or multiple profiles from one sheet (called nesting). CR can cut boards to size, outer edges, profile slots and drill holes through the skin of the material. When using a CNC Router or Machining centre, a suction bed is required to rigidly hold the material (some machines have physical clamps). Suction beds have pods for raising the work above the table for edge profiling or undercutting.

Dust extraction and collection is critical to ensure adequate chip removal to carry the chips away from the work piece. Feeds and speeds can be adjusted to increase the chip load and take heat away from the cutter, but the dust collection system must be powerful enough to remove chips from the work area. Good housekeeping will also mean that collets, collet nuts and spindles should be continually maintained as dust build up will affect performance.

Compression Router Geometry

Helix angles required for woodworking are considered low when compared to metal cutting tools. A helix angle range between 22° to 30° would be considered in many wood applications. But clearance angles used are a lot higher with materials such as Medium Fibre Density (MDF) board due to “spring back” after separation from the chip. This “spring back” of the material is why multiple OD back offs are used on a CR and clearance angles between 15-20° are standard.

As a rule, when machining softer materials larger Rake Angles can be used. Particularly when cutting wood and MDF, a larger Rake angle will lift fibres rather than flatten them. When machining wood materials, insufficient clearance angles, with smaller Hook Angles can have the following negative effects:

  • Increased tool wear
  • Raised or fuzzy grain
  • Burning or Glazing of the material

In addition to the tool geometry, the operator must also consider the following

  • Grain directions in the material
  • Spring back of the material during the cut
  • The wear rate of the cutting edge and how it reacts to the material being cut
  • Resins in hard and softwoods
  • Glues included in the sandwich materials such as plywood
  • Contaminates included in materials like chipboard