Reaming finishes an existing hole. Start with the exact reamer’s cutting data and allowance recommendation, not a universal fraction of a drilling speed.
Use the correct feed convention
Metric RPM = 1000 × cutting speed in m/min /(π × reamer diameter in mm). If the supplier specifies feed per revolution, feed in mm/min = RPM × mm/rev. If it specifies feed per tooth, multiply by the number of effective cutting teeth as directed. Confusing these conventions can change feed severalfold.
For an illustrative 10 mm reamer at 20 m/min, RPM is 636.620. If the selected tool data calls for 0.15 mm/rev, the resulting feed is 95.493 mm/min. These invented values explain the calculation; they are not recommended settings for every 10 mm reamer.
Diametral allowance versus stock per side
Reaming allowance on diameter is finished diameter minus pre-hole diameter. A 9.80 mm pre-hole for a 10.00 mm finished hole leaves 0.20 mm diametral allowance, or 0.10 mm per side. State which one you mean when comparing recommendations.
Too little stock can promote rubbing; too much can overload the tool or pack chips. The correct allowance depends on size, material, tool construction and hole conditions. A reamer generally follows the existing hole rather than reliably correcting a large position error. A boring operation may be needed when location or straightness must be corrected.
Troubleshooting sequence
For oversize, taper or chatter, check runout, holder condition, pre-hole geometry, alignment and workholding before changing feed. Inspect chip evacuation and coolant delivery, especially in blind holes. Verify measurement technique and part temperature when tolerances are small.
Supplier rules of thumb about reaming more slowly or feeding harder than drilling are starting context, not a substitute for the actual tool’s data. Reamer geometry, carbide versus HSS construction and work material can change the operating window. Record the stable settings with the tool part number and material grade.
A manufacturer starting-data example
The selected values below come from Hannibal Carbide Tool’s REAM rows, General Purpose (G.P.) columns. Feed values are for a 1/2 in hole diameter and are inches per revolution, not per tooth. Use them only in the context of that manufacturer’s applicable tooling and material classification; they are not HSS, PCD or universal reamer recommendations.
| Supplier material group | Hardness in source | G.P. speed, SFM | G.P. feed at 1/2 in, IPR |
|---|---|---|---|
| Aluminum, cast/wrought; examples include 6061 | 30–150 HB, source indicates 500 kg | 150–250 | 0.011 |
| Low/medium-strength wrought steel | 100–375 HB | 30–85 | 0.011 |
| 300-series stainless; examples include 304/316 | 135–375 HB | 40–75 | 0.006 |
The source separately lists coolant-fed values and feeds for other diameters. Do not slide across those columns accidentally. Confirm tool construction, material condition, allowance and application with the supplier before using a starting row.
Convert one row into machine units
For a calculation example, select 50 SFM within the listed stainless speed range and use the 0.500 in diameter and 0.006 IPR entry. RPM = 50 × 12/(π × 0.500) = 382.0. Feed = 382.0 × 0.006 = 2.292 IPM, approximately 58.21 mm/min. The feed per revolution is 0.006 × 25.4 = 0.1524 mm/rev. Do not multiply this IPR value by flute count.
The chosen 50 SFM is an illustrative selection inside a published range, not a demonstrated optimum. Preserve the actual diameter and feed convention when using the RPM/feed arithmetic tool. Its drilling label does not supply or validate reaming cutting data.
Close the loop with the pre-hole
Record pre-hole size at entry and depth, diametral stock, runout and finished-hole measurements. A feed calculation cannot correct a misplaced pre-hole or establish the appropriate allowance. If the hole is oversize or tapered, investigate alignment, stock distribution, holder and evacuation before assuming that a faster or slower feed will solve it.
Content updated October 8, 2026. Sources and numerical examples are explained above; examples are not production test results. Editorial method · Report a correction.
References and verification
Original explanations and worked examples by MfgWorkbench. Sources below support the stated concepts or selected reference data; they do not certify every example or a production application.
For a correction, send the page URL, the affected value and supporting documentation through our contact page.