Reaming is the precision finishing operation that takes a drilled hole from rough to exact. A standard twist drill produces a hole that is slightly oversize relative to the drill nominal diameter, not perfectly round, and with a surface finish too rough for bearing and bushing fits. A reamer follows the drilled hole, removing a small amount of additional material to bring the hole to exact diameter, improve its roundness, and produce the smooth surface finish required for precision fits.
The difference between a drilled hole and a reamed hole is the difference between a hole that is approximately the right size and one that is exactly the right size. In hydraulics, pneumatics, bearing housings, and precision assembly, that difference is everything. Reaming is the standard finishing operation for holes specified to H7 tolerance and tighter, which is the precision fit tolerance used for rotating shafts, bushings, and precision locating pins throughout American manufacturing.
Reamer Types and Their Applications
Hand reamers are turned by hand using a tap wrench. They have a long, gentle taper lead that guides the reamer into the drilled hole and aligns it before the cutting flutes begin to remove material. Hand reamers remove small amounts of material (0.001 to 0.005 inch per side maximum) and should be used after drilling to within 0.010 inch of the final hole size. They are the standard finishing tool for bearing and bushing fits in toolroom and repair shop work.
Machine reamers are run in a drill press, lathe, or machining center. They have a shorter, more aggressive lead and cut faster than hand reamers. Machine reaming is the production standard for finishing precision holes at volume, where hand reaming would be too slow for economical production rates.
Adjustable hand reamers have an expanding body that allows the cutting diameter to be adjusted within a range, typically a spread of 1/32 inch to 1/16 inch. They are used when a single fixed-size reamer is not available for the exact hole size needed, and in field service work where carrying a full set of individual reamers is impractical.
Taper reamers produce Morse taper and similar standard taper bores for tool-holding and center-mount applications. They are ground to the exact taper angle of the standard they produce and are used to refine taper bores that have been rough-drilled or that need reconditioning.
For comprehensive guidance on hand reamers, see our blog on hand reamers explained. For the HSS cutting tools that reamers complement, see our HSS cutting and finishing tools. For drilling tools, see our boring and drilling tools.
Frequently Asked Questions — Reamers
A reamer is used to enlarge a drilled hole to a precise final diameter, improve its roundness, and produce a smooth surface finish suitable for bearing and bushing fits. Reaming follows rough drilling and removes only 0.001 to 0.005 inch per side, producing a hole that meets the tight diameter tolerances required for precision assembly fits that a drill alone cannot achieve.
The three main types of reamers are hand reamers, machine reamers, and adjustable reamers. Buyohlic offers quality reamers designed for accurate hole finishing and precision work.
A drill bit creates a hole, while a reamer improves its size, accuracy, and finish. Buyohlic reamers deliver tighter tolerances and smoother surfaces than drilling alone.
Mount the reamer in a tap wrench by its square shank. Align the reamer with the drilled hole using the tapered lead section as a guide. Rotate clockwise only (never reverse a reamer as this dulls the cutting edges). Apply steady downward pressure while rotating. Use cutting oil throughout the reaming operation on steel and other hard metals. Remove the reamer rotating clockwise only, maintaining forward pressure to prevent the edges from marking the hole wall during withdrawal. Measure the finished hole size with a telescoping gauge and micrometer.
Drill to 0.005 to 0.010 inch undersize and ream to final diameter. For example, to finish a 0.500 inch H7 hole, drill 0.490 to 0.495 inch and ream to 0.500 inch. Leaving too much stock overloads the reamer and produces a poor finish. Leaving too little stock means the reamer does not cut consistently around the full circumference, leaving an uneven finish.
For best results, leave approximately 0.2 mm to 0.5 mm of material for reaming. Buyohlic recommends following the reamer manufacturer’s specifications for optimal accuracy.
The drilled hole should be slightly smaller than the final desired size, usually by 0.2 mm to 0.5 mm. Buyohlic reamers then accurately finish the hole to exact dimensions.
