The Know-How of Compression Bits

Compression Bits

Compression cutters combine both up-cut and down-cut spirals to force chips into the centre of the panel. The inwards pressure prevents chipping on either surface and stabilises the workpiece.

Counteracting cutting forces compress the material and stabilise the workpiece, creating a superior finish on the top and bottom of the part.

Carbide compression leaves a superb finish on both faces of the board when milling, grooving and sizing. The raw rod is sourced from premium quality carbide powder and machined to perfection for a long-lasting product.

  • Balanced cutting force
  • Forces chips towards the centre of the panel
  • Excellent for laminates and veneers

For compression cutter milling, use 2 wing for MDF and 3 wing for chipboard to allow for  the chip flow which causes heat and wear. 3 wing cutters run faster than 2 wing and 1 wing due to the extra cutting edges. 

What is the length of the up-cut?

The ideal amount of up cut is roughly ½ the thickness of the board you are cutting when milling. However, when rebating or grooving the depth of the groove must be greater than the length of the up-cut or there will be chipping on the top surface.

The size of the up-cut is dependent on the diameter of the bit.

  • 8mm diameter has an up-cut of 5mm
  • 10mm diameter has an up-cut of 7mm
  • 12mm diameter has an up-cut of 9mm

How do I calculate the feed speed of my compression cutters?

Feed rates are calculated based on three major factors:

  1. Number of cutting edges (2 wing for MDF and 3 wing for chipboard)
  2. Feed coefficient (All other factors i.e. board quality, vibrations, environment and material)
  3. Rotational speed RPM

Watch this quick clip for more info:

Machine operators often refer to a ‘sweet spot’ in machining. However, there is a wide range of workable parameters. So long as the chip load is acceptable for the geometry of the tool, and the material being machined, there is no reason why speeds of 50 or 100 metres per minute can’t be achieved. Therefore, getting the chip load correct is incredibly important.

When the chip load is too low, this causes re-cutting and generates unnecessary heat. When chip load is too high the cutter is labouring and tool flex can occur.

How do I protect my tooling?

Tools should be replaced at the first sign of edge deterioration, to prevent further damage to tool holders. 

Feed tooling slowly enough so that it is not under significant strain while maintaining momentum to avoid burning.

Do not use adaptor bushings to reduce the size of the collet.

Use the right router bit for the right job and avoid unnecessary wear

Regularly check the router mechanism

Inspect tools for collet marks which indicate slipping or dust build-up. Check collet for wear.

2 wing vs. 3 wing cutters

  • 2 wing cutters have larger flutes that allow for better chip flow. Dust and particles are able to escape the tool flutes more easily to then be collected by your dust extraction. Poor chip flow results in dust and particles clogging up the tool flutes and create unnecessary friction and heat. Heat is the main cause of tool deterioration. Reducing the amount of heat on your cutters keeps your tools sharper for longer
  • Having a separate cutter for chipboard and MDF has many advantages. Chipboard is harsher on tools than MDF and causes the cutting edge to deteriorate inconsistently. This can result in a slightly streaky finish which you can’t see easily on chipboard but is very obvious on MDF. MDF also has very fine dust which can cause build-up on any tooling with heat and poor chip flow which is why using a 2 wing cutter extends the tool lifespan. Chipboard particles are less likely to do this, so 3 wing cutters are recommended for a quality  finish and fast production speeds
  • 2 wing cutters are less expensive than 3 wing cutters
  • Caution: 2 wing cutters need to be run at slower feed speeds than 3 wing cutters to allow for the same amount of chip flow through fewer flutes. Alternatively, for the same feed speed, 2 wing cuttersmust be run at a higher RPM. For more information about feed speeds please refer to the following video: