Machining knowledge, made practical
Interactive TechTip
Set the bar, the surface speed and the feed. You get spindle speed, feed rate and removal rate — plus the theoretical surface finish that feed and nose radius will actually produce.
Theoretical surface finish
Surface finish varies with the square of the feed. Halve the feed and the theoretical Ra drops to a quarter — but so does your feed rate, and with it the cycle time.
Ra is inversely proportional to nose radius. Going from 1/64" to 1/32" halves the finish figure at the same feed, which is usually cheaper than slowing the machine down.
These numbers are what the geometry alone would give. Vibration, built-up edge, a worn edge or a flexing setup only make it worse — never better. Treat the result as the best case.
Ready to cut
Once the geometry is settled, the grade and the holder decide how long it lasts. Browse the turning line built to hold tolerance under aggressive feeds.
FM Carbide Turning Inserts → Tool Holders Boring Bars Grade Look-UpFinish is calculated from the standard circular-arc model: Rmax = f² / (8r) and Ra = f² / (32r), with RMS taken as 1.11 × Ra. A 0.2 mm feed on a 0.8 mm nose radius returns 1.6 µm, which matches the published reference value. Removal rate assumes a continuous cut at full depth.
Ready to cut
Once the geometry is settled, the grade and the holder decide how long it lasts. Browse the turning line built for tight tolerances under aggressive feeds.
Not sure which grade matches your material? Use the Grade Look-Up.