Feed Per Revolution
Is feed per revolution the same as chip load?
No. Chip load is the amount each cutting edge removes per tooth; feed per revolution is the total linear advance per spindle revolution, which in milling equals chip load multiplied by flute count.
Why is feed per revolution preferred on lathes?
Because the work or tool rotates, and tying feed directly to spindle rotation keeps chip thickness more stable as spindle speed changes.
How do you convert feed per revolution to linear feed?
Multiply by RPM: IPM = IPR × RPM or mm/min = mm/rev × RPM.
Feed per revolution is the linear distance a cutting tool advances for each spindle rotation, expressed in in/rev or mm/rev. It is the standard feed specification in CNC turning, drilling, and reaming, where feed rate (IPM) equals feed/rev multiplied by RPM. In milling, feed per revolution is derived from chip load per tooth multiplied by flute count, then converted to feed per minute.
On the shop floor, feed per revolution is fundamental in CNC lathe operations. When programming a turning pass at 0.20 mm/rev, the tool advances 0.20 mm for every spindle revolution regardless of speed changes. This ensures chip thickness and surface finish remain consistent as RPM varies due to constant surface speed or tool wear compensation. In milling cells, the same concept is used as an intermediate calculation: a drill or endmill with known chip load per tooth requires the control feed to be set so distance per revolution matches desired chip load after accounting for flute count. Production machinists rely on feed-per-rev scaling when spindle RPM changes, because it automatically adjusts linear feed to maintain stable cutting conditions. This is critical in grooving, parting, drilling, and reaming where chip load is directly tied to rotation.
Wrong modal selection: Programming feed-per-rev while the control is in feed-per-minute mode causes axis movement at the wrong rate, especially on lathes where G95 is the standard feed-per-rev code.
Ignoring RPM scaling: When spindle speed drops but feed/rev stays fixed, linear feed drops accordingly, shifting surface finish and cycle time unexpectedly.
Milling assumptions on lathes: Treating a lathe like a mill and calculating only chip load without accounting for per-revolution motion can lead to excessive tool load, poor chip evacuation, or chatter.