GlossaryKind of term: Manufacturing termFeed per tooth (fz)
What is feed per tooth?
Feed per tooth fz is how far a cutter advances per cutting edge, in mm; with the number of teeth and the spindle speed it gives the feed rate.
The distance counts in the feed direction while one cutting edge passes through the material, so the unit is millimetres per tooth. The feed rate follows from it: vf = fz × z × n, where z is the number of teeth and n the spindle speed. A four-flute cutter at 6,000 rpm and an fz of 0.05 mm travels at 1,200 mm/min. In turning and drilling the counterpart is feed per revolution f, in mm/rev.
What does feed per tooth depend on?
fz is not the same as chip thickness. The maximum chip thickness equals fz only when the cutter is engaged across at least half its diameter and the edge stands square to the surface. The chip gets thinner at a smaller width of cut, and also at a small lead angle, as on high-feed cutters. Catalogues therefore often give a chip thickness, or an fz that you raise at low engagement. The right fz depends on the tool, the material, stability and the purpose of the pass: roughing usually takes a larger fz than finishing.
How does feed per tooth work in practice?
The feed rate sets how long a pass takes, and with it much of the machining time. More flutes give a higher feed rate at the same fz but less room for chips, which can pack in a deep pocket in aluminium. Too small an fz makes the edge rub instead of cut, which costs tool life, especially in austenitic stainless steel, which work-hardens. A larger fz usually leaves a rougher surface in finishing, so a tight roughness requirement can limit the feed in the final pass.
What is feed per tooth often confused with?
Feed per tooth is not feed rate: fz is the bite per cutting edge, vf the speed at which the tool moves relative to the workpiece. Nor is it feed per revolution, which is fz times the number of teeth. And fz is not always the chip thickness, as described above.
Frequently asked questions
How do you convert feed per tooth to feed rate?
Feed rate vf = fz × z × n: feed per tooth times the number of teeth times the spindle speed. In turning it is vf = f × n, with f the feed per revolution.
Why raise the feed at a narrow width of cut?
Because the chip gets thinner than fz once the cutter is engaged across less than half its diameter. At the same fz the edge starts rubbing. A higher fz brings the chip thickness back to what tool and material need, and the pass runs faster.
Is a cutter with more flutes faster?
At the same fz it runs faster, as long as the chips can get out and the setup is stable. In aluminium and deep pockets you often choose fewer flutes for chip room; in steel and for finishing, often more.