The spiral direction of a CNC cutter affects chip evacuation, top and bottom edge quality and the forces acting on the workpiece. Selecting the correct geometry is particularly important when machining plywood, laminated boards, wood and plastics.
Upcut cutter
An Upcut spiral pulls chips upwards and out of the cut. It provides good chip evacuation and effective tool cooling.
It is suitable for deeper slots, pocketing and applications where reliable chip removal is important. It generally produces a cleaner bottom edge but may lift fibres or chip the laminate on the upper surface.
Downcut cutter
A Downcut spiral pushes chips and cutting forces downwards. This helps produce a clean top edge and reduces damage to the upper surface.
It is suitable for laminated boards, plywood and decorative surfaces. Chip evacuation is less efficient in deep cuts, which can increase heat. Suitable cutting depth, feed rate and spindle speed are therefore essential.
Compression cutter
A Compression cutter combines both spiral directions. The lower section cuts upwards while the upper section cuts downwards, directing the cutting forces towards the centre of the material.
When used at the correct depth, it can create a clean edge on both faces. It is ideal for full-depth profiling of laminated boards and plywood.
The transition between the two cutting sections must remain inside the material during the finishing cut.
Which cutter should you choose?
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Upcut: efficient chip evacuation and a clean bottom edge.
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Downcut: clean upper surface.
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Compression: clean top and bottom edges when correctly applied.
Always carry out a test cut and set the spindle speed, feed rate and cutting depth for the specific tool and material.