Work out how many passes a slot needs and how long they take. Enter slot width, slot depth, tool diameter and feed per tooth to get the pass count and the total cycle time.
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Request a Proposal →A full-width slot is the hardest routine cut a milling cutter does. Radial engagement is 100% of the cutter diameter, so the cutting edge enters and leaves the material along the full arc, the chip has nowhere to escape, and the cutter has no room to cool. That single fact drives every number on this page.
Two consequences follow. First, chip evacuation becomes the limiting factor, not cutting speed — recutting chips is what breaks small slotting cutters. Second, axial depth must come down. As a starting point in steel, keep the first pass at 0.5 × diameter and work up only if the machine is rigid and the coolant reaches the cut.
10 mm solid carbide 4-flute end mill, full-width slot in 6082 aluminium, Vc 300 m/min, fz 0.05 mm/tooth, depth 5 mm.
When you can avoid a full-width slot, do. A cutter 20–30% smaller than the slot, entered by helical or trochoidal ramping, spreads the load across a much longer edge length and lets the tool run several times faster. The material comes out either way; only one of the two methods is kind to the cutter.
Never measure a slot with the cutter that made it and assume it is to size. Carbide cutters cut oversize as they wear and undersize when they deflect. Cut the slot, measure it, then adjust the wear offset — not the programmed dimension.
When a slot is wider than the tool diameter, multiple passes are needed. This calculator determines the number of passes and estimates cycle time based on slot width, tool diameter, feed rate, and number of depth steps.
For width ≤ tool diameter, slot in one pass at 50-70% of normal feed rate. For width > tool diameter, multiple passes allow higher feed in each pass and produce straighter slot walls. Never slot at full diameter and full feed -- the 180 deg engagement overloads the tool.
For roughing wide slots: trochoidal or adaptive clearing (especially in hard materials). For finishing: contour passes with 0.1-0.2 mm radial stock. Avoid plunging directly into the slot -- ramp or helix entry reduces impact on the tool centre.
Down-milling (climb milling) produces better surface finish and lower cutting forces. However, in a full slot, both up and down occur simultaneously (one side climbs, the other side conventional mills). For wide slots with multiple passes, use climb milling on each pass.
Enter the slot width, tool diameter, feed rate, and number of Z-level passes. The calculator shows how many lateral passes are needed and estimates the total machining time for the slot. For deep slots, also use the peck drilling calculator for drilling before slotting.
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Use the calculator freely. If the result points to a tooling or process problem, we can source the exact carbide tooling you need from vetted factories in China. Compare factory-direct pricing.
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CUTTING SLOTS? Slot widths are specified in tenths, which puts both tool tolerance and shank quality under pressure. See how tolerances are written into a tool inquiry.
Slotting is a full-width engagement, which is the hardest thing you can ask of a cutter. Send the slot width, depth and material.