Speeds and feeds
Feed rate conversion calculator: IPR, IPM and feed per tooth
IPM = RPM x IPR; 850 RPM at 0.008 IPR is 6.80 IPM (172.72 mm/min).
Technical review pending. Formulas and values are cited. This notice comes down after a machinist review.
Feed rate
IPM
IPM = RPM x IPR = 850 x 0.008 = 6.80 IPM
Starting point. 172.72 mm/min; 0.0080 IPR.
| Feed | Result | Formula with your numbers |
|---|---|---|
| Feed rate, inch (IPM) | 6.80 IPM | IPM = RPM x IPR = 850 x 0.008 = 6.80 IPM |
| Feed per revolution, inch (IPR) | 0.0080 IPR | Given |
| Feed per tooth, inch (IPT) | 0.0080 in/tooth | IPT = IPR / Z = 0.008 / 1 = 0.0080 in/tooth |
| Feed rate, metric (vf) | 172.72 mm/min | vf = IPM x 25.4 = 6.8 x 25.4 = 172.72 mm/min |
| Feed per revolution, metric (fn) | 0.20 mm/rev (0.2032 mm/rev) | fn = IPR x 25.4 = 0.008 x 25.4 = 0.2032 mm/rev |
| Feed per tooth, metric (fz) | 0.20 mm/tooth (0.2032 mm/tooth) | fz = IPT x 25.4 = 0.008 x 25.4 = 0.2032 mm/tooth |
Source: Machinery's Handbook (feeds and speeds formulas). Metric conversion at 25.4 mm per inch.
Feeds are starting points. Adjust by chip, sound and finish.
How it works
Inch
IPM = RPM x IPR; IPM = RPM x IPT x Z; IPR = IPT x Z
| Symbol | Meaning | Unit |
|---|---|---|
| RPM | Spindle speed | rev/min |
| Z | Number of flutes (cutting edges); 1 for turning | count |
| IPM | Inches per minute, the table or carriage feed rate | in/min |
| IPR | Inches per revolution, feed per turn of the spindle | in/rev |
| IPT | Feed per tooth, also called chip load | in/tooth |
Metric
vf = RPM x fn; vf = RPM x fz x Z; fn = fz x Z
| Symbol | Meaning | Unit |
|---|---|---|
| vf | Feed rate | mm/min |
| fn | Feed per revolution | mm/rev |
| fz | Feed per tooth | mm/tooth |
| 25.4 | Millimeters per inch: mm/min = IPM x 25.4, mm/rev = IPR x 25.4, mm/tooth = IPT x 25.4 | mm/in |
Run any formula backward to go the other way: IPR = IPM / RPM and IPT = IPM / (RPM x Z). The speeds and feeds math behind these numbers, with RPM and metal removal rate, is laid out on the machining formulas page.
Worked example: turning, IPR to IPM
A lathe at 850 RPM with a 0.008 IPR feed (Z = 1).
- IPM = 850 x 0.008 = 6.80 IPM.
- fn = 0.008 x 25.4 = 0.2032 mm/rev, shown as 0.20 mm/rev.
- vf = 6.80 x 25.4 = 172.72 mm/min.
Result: 6.80 IPM, 0.20 mm/rev, 172.72 mm/min.
Worked example: milling, IPM back to chip load
A 3-flute end mill at 3,000 RPM, programmed at 15.0 IPM.
- IPT = 15.0 / (3,000 x 3) = 15.0 / 9,000 = 0.0016667 in, shown as 0.0017 in per tooth.
- IPR = 15.0 / 3,000 = 0.0050 in per revolution.
- vf = 15.0 x 25.4 = 381.00 mm/min.
- fz = 0.0016667 x 25.4 = 0.0423 mm, shown as 0.04 mm per tooth at 2 places.
Result: 0.0017 in per tooth, 0.0050 IPR, 381.00 mm/min.
Worked example: metric chip load to feed rate
A 4-flute end mill at 2,500 RPM and 0.05 mm per tooth.
- vf = 2,500 x 0.05 x 4 = 500.00 mm/min.
- IPM = 500 / 25.4 = 19.6850 IPM, shown as 19.69 IPM.
- IPT = 0.05 / 25.4 = 0.0020 in per tooth.
Result: 500.00 mm/min (19.69 IPM), 0.0020 in per tooth.
Shop notes
- On a lathe, IPR is the setting the feed gearbox uses, and the CNC feed-per-revolution mode (G99 on a Fanuc-style lathe in G-code system A). IPM changes whenever RPM changes.
- In milling, the tool maker gives the chip load. The feed rate follows from it with IPM = RPM x IPT x Z.
- Same numbers as the machining formulas page: 764 RPM x 0.002 in per tooth x 4 flutes = 6.112, or 6.1 IPM.
- Mixing systems is the usual mistake: an IPR feed entered as mm/rev is 25.4 times too light.
FAQ
How do you convert IPR to IPM?
Multiply feed per revolution by spindle speed: IPM = RPM x IPR. 850 RPM at 0.008 IPR is 6.80 IPM (172.72 mm/min).
How do you get chip load from feed rate?
IPT = IPM / (RPM x Z). 15.0 IPM at 3,000 RPM on 3 flutes is 15.0 / 9,000 = 0.0017 in per tooth.
What is 0.008 IPR in mm/rev?
0.20 mm/rev: 0.008 x 25.4 = 0.2032 mm/rev.
Is IPR the same as chip load in milling?
No. IPR = IPT x Z, so a 3-flute cutter at 0.00167 in per tooth feeds 0.0050 in per revolution (15.0 IPM / 3,000 RPM). On a single-point lathe tool, Z is 1 and the two are the same number.
What is 500 mm/min in IPM?
19.69 IPM: 500 / 25.4 = 19.6850 IPM.
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