Reaming

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Revision as of 21:49, 9 September 2007

Reaming is the process of enlarging a hole or a bore to an exact diameter. Reaming can also be used to smooth out a hole or a bore. The tool used for reaming is called a reamer. Reamers are fluted, edge cutting tools that come in two flavor -- machine/chuck reamers and hand reamers. Chucking reamers can be used in lathes, drill presses, and screw machines. Hand reamers have a square drive and can be turned with a wrench.

Generally, reaming is done after the machinist drills a hole at a slightly smaller size. The difference between the reamer's diameter and the drill's diameter is called the allowance. Modern drills are relatively precise, but the use of reamers allow for the machinist to produce a near perfect hole.

Reamers consist of either a set of parallel straight cutting edges or helical cutting edges along the length of the cylindrical body. Reamers must utilize hardness in its cutting edges for long life and toughness to prevent failure under normal stresses of use. Spiral edges may be be oriented clockwise or counter-clockwise depending on the desired usage. A tapered reamer with a clockwise spiral will tend to self feed, which can possible lead to wedging and breakage, whereas a counter-clockwise spiral spinning in a clockwise direction would be less prone to this.

Spiral Fluted Machine Reamer

Material

Reamers are typically made from high speed steel and solid carbide or from a steel alloy body with a carbide tip. Combination reamers are made out of carbide, cobalt, or high-speed tooling. Reamers may also be surrounded by a thermal coating. The coating protects the reamer from heat, pressure, coolant, and workpiece material. Typical coatings are titanium nitride and titanium carbonitride. Reamers with titanium nitride coatings should be used on shallow holes. Reamers with titanium carbonitride may be used on all abrasive materials.

Drill Bit vs. Reamer Tolerances

A standard drill bit has a diametrical tolerance of about .002", while as improved drill bits can have diametrical tolerances of .001". These tolerances may not be good enough for certain engineering applications. It is for this reason that reamers are necessary. Reamers have diametrical tolerances of +0.0002/-0.0000 for sizes up to 1/2", and +0.0003/-0.0000 for sizes 1/2 thru 5/8". Although the best reamers have diametrical tolerances of up to .0008"

Variations of Reamers

Straight Reamer - used to make minor enlargements to a hole
Rose Reamer - used as roughing reamers
Shell Reamer - used for reaming bearings
Tapered Reamer (precision) - used to make tapered holes to later receive a tepered pin
Combination Reamer - used to reduce the number of turret operations in parts with multiple internal diameters
Tapered Reamers (non-precision) - used for cleaning burrs from a drilled hole or to enlarge a hole

The Final Product

The finish in the reamed hole is determined by several things:

1. Sharpness and quality of the grind finish of the tool.
2. The type of material being reamed.
3. The skill of the operator
4. The setup.
5. The coolant. (if used)
6. Cutting speed and feed

Sources:
http://en.wikipedia.org/wiki/Reamer
http://www.cutting-tool.americanmachinist.com/guiEdits/Content/bdeee16/bdeee16_1.aspx
http://www.mcmaster.com/ctlg/DisplCtlgPage.aspx?ReqTyp=CATALOG&CtlgPgNbr=2430&term=About%2bChucking%2bReamers&sesnextrep=442618588470951&ScreenWidth=1024&McMMainWidth=817
http://reviews.ebay.com/Reaming-Practices_W0QQugidZ10000000002397670

Charles Yee, Luke Miller, Terry Chau