Free Machine Reamer Speed & Feed Calculator
Calculate pre-drill hole diameter, stock removal allowance, spindle RPM, and feed rate for HSS and carbide chucking reamers across common metals.
⚙️ Hole Size, Material & Tooling
Leave 0.015" (0.38 mm) on diameter for clean reamer cutting
• Half the Speed, Double the Feed: Run spindle speed at 1/2 to 2/3 of drilling speed, but double or triple the feed per revolution.
• Never Stop Spindle in Hole: Retract reamer with spindle turning to prevent scoring walls.
The "Too Little Stock" Trap: If you leave too little stock (less than 0.005" / 0.12mm), the reamer flutes cannot bite into the parent metal; instead, they rub, burnish, work-harden the hole, and dull the cutting edges instantly. Always leave enough stock for the reamer to cut a true chip!
Recommended Tools & Equipment
Tested hardware and components for high reliability
The Purpose of Machine Reaming
Standard twist drills do not create round, straight, or size-accurate holes due to chisel edge walk and web deflection. A chucking reamer produces precision round bores with tight tolerances ($pm 0.0002"$ to $pm 0.0005"$) and mirror-smooth surface finishes (16 to 32 Ra micro-inches).
Standard Stock Allowance Guidelines
- Holes under 1/4" (6 mm): Leave $0.008" - 0.010"$ (0.20 mm - 0.25 mm) on diameter.
- Holes 1/4" to 1/2" (6 - 12 mm): Leave $0.012" - 0.015"$ (0.30 mm - 0.40 mm).
- Holes 1/2" to 1" (12 - 25 mm): Leave $0.015" - 0.020"$ (0.40 mm - 0.50 mm).
- Holes over 1" (25 mm): Leave $0.020" - 0.025"$ (0.50 mm - 0.65 mm).
Speed and Feed Principles
The classic machinist rule for reaming: Half the Speed, Twice the Feed. Reamers only cut on their 45° chamfer lead angle at the front; the cylindrical body only guides the tool. Running too fast causes chatter and bell-mouthing, while high feed ensures positive chip shearing.
Frequently Asked Questions
Why did my reamer cut an oversized hole?
The most common cause of oversized reamed holes is spindle-to-toolholder runout. Even 0.001" of chuck runout will make the reamer cut 0.002" oversize. Use a floating reamer holder or collet chuck with < 0.0002" TIR.
Can I ream without cutting fluid?
Never ream dry in metals! Reaming requires abundant high-lubricity cutting oil or rich coolant to lubricate the cylindrical guide margins, flush fine chips, and prevent built-up edge (BUE) from tearing the bore surface.
Why should I use a left-hand spiral reamer for cross-holes?
When reaming a bore with an intersecting cross-hole, oil port, or keyway, straight flutes will drop into the gap, catch on the edge, and shatter. A left-hand spiral (right-hand cut) bridges across the interruption smoothly without hooking.