Understanding reaming vs drilling is the difference between a hole that is roughly the right size and one that fits a pin or bushing with precision. Each tool has a job, and using them together gives the best results.
What a Drill Bit Actually Does
A twist drill removes a lot of material quickly, starting a hole from solid stock. It is built for speed and material removal, not for tight tolerance or a mirror finish. Because the cutting happens at two lips and the bit can wander or flex slightly, a drilled hole is often a few thousandths oversize, may be slightly out of round, and can show a rougher wall. For most general fastening and clearance holes, that is perfectly fine.
What a Reamer Does
A reamer does not create a hole from solid material. Instead it enlarges and refines an existing drilled hole by a small amount, cutting on many flutes at once. That multi-flute action produces a hole that is accurately sized, round, straight, and smooth. Reamers are the tool of choice when a hole must match a dowel pin, a bearing, or a precision bushing.
When to Reach for a Reamer
- Tight tolerance: When the hole diameter must hold within a few thousandths of an inch.
- Slip or press fits: Dowel pins, alignment pins and bushings need the roundness only a reamer delivers.
- Better finish: When the hole wall needs to be smooth, not torn.
- Straightness: When the hole must stay true through a thicker workpiece.
The Right Way to Ream
The secret is leaving the correct amount of stock. Drill the hole slightly undersize, then let the reamer remove that thin remaining layer. Too much stock overloads the reamer; too little and it burnishes instead of cuts. Run reamers slower than drills, feed steadily, use cutting fluid on metal, and never spin a reamer backward, which dulls the cutting edges. Our reamer technical data lists recommended drill sizes for common reamer diameters.
Quality Tools Matter
Because a reamer is a finishing tool, edge quality is everything. A well-ground, American-made reamer holds size and finish far longer than a bargain import. Pairing a sharp drill bit with a quality reamer is how machinists get repeatable, precise holes.