Reaming Guide — Speeds, Feeds & Stock Allowance

What Reaming Actually Does

A drill bit cuts a hole through a combination of cutting and tearing action at the chisel point — it produces a hole that's round but not perfectly so, with a rougher surface finish and looser tolerance than many applications require. A drilled hole typically lands within ±0.005 to ±0.010 inches of nominal diameter with a surface finish around 125–250 microinches Ra.

A reamer removes a small, controlled amount of material from an already-drilled hole using multiple cutting edges working simultaneously around the circumference. This produces a much rounder, straighter hole with tighter tolerance — typically ±0.0005 to ±0.001 inches — and a smoother finish around 16–32 Ra. Reaming doesn't correct hole location or major out-of-round error from drilling; it follows the existing hole and refines size and finish.

Stock Allowance — How Much to Leave for the Reamer

Stock allowance is the single most important variable in successful reaming. Leave too little material and the reamer skates over high spots without fully cleaning up the hole, leaving witness marks or undersized sections from the original drill. Leave too much and the reamer is forced to remove material like a drill rather than finish like a reamer — this causes excessive cutting force, chatter, bell-mouthing at the entrance, and rapid reamer wear.

Always drill with a bit sized specifically for reaming stock — don't assume a standard tap-drill-style chart applies. If you don't have the exact undersized drill, go slightly smaller rather than larger. A hole reamed from slightly too little stock can be re-reamed with a second pass. A hole reamed from too much stock is often scrapped or oversized beyond tolerance.

Reaming Speeds by Material

Reaming SFM runs roughly half of drilling SFM for the same material — the multiple cutting edges and finish requirement demand a gentler approach than aggressive material removal. Going too fast causes chatter and poor finish rather than tool breakage, which is the more common failure mode in reaming versus drilling or tapping.

Reaming Feed Rate Reference

Feed rate in reaming is typically 2–3 times higher than the equivalent drill feed for the same diameter, because the reamer is removing a thin, controlled chip across multiple flutes rather than the full hole diameter at once. A higher feed actually helps surface finish in reaming up to a point — too low a feed can cause the reamer to rub rather than cut cleanly, leading to built-up edge and poor finish, especially in softer materials like aluminum.

Hand Reaming vs Machine Reaming

Hand reamers have a long tapered lead (typically 8–10 flutes of taper) that gradually engages the hole, allowing the operator to feel resistance and control entry by hand with a tap wrench. They're designed for slow, controlled rotation — one revolution at a time — and are common for fitting dowel pins, finishing holes in the field, or precision work where machine power-feeding risks tearing the surface.

Machine reamers (chucking reamers) have a short chamfer and are designed to run at calculated RPM and feed in a drill press, mill, or CNC machine. They're the standard for production work where consistency matters. Never run a hand reamer at machine speed — the long taper isn't designed for rapid engagement and will produce a torn, oversized hole. Never hand-turn a machine reamer expecting hand-reamer results — the short chamfer engages too abruptly for controlled hand feel.

Full decision fork (when hand wins, when chucking is required, spiral vs straight, wrong-tool failures): Hand Reaming vs Machine Reaming — Which to Use.

Common Reaming Problems and Fixes

For exact RPM and feed on your reamer size and material, use the Reaming Speed and Feed Calculator. Related tools: Tapping Speed and Feed Calculator, Drill Speed Calculator, and Tap Drill Size Calculator.