Reamer
Precision reamers are designed to enlarge the size of a previously formed hole by a small amount but with a high degree of accuracy to leave smooth sides.
A typical reamer consists of a set of parallel straight or helical cutting edges along the length of a cylindrical body.
Reamers must combine both hardness in the cutting edges, for long life, and toughness, so that the tool does not fail under the normal forces of use.
For example, a tapered hand reamer with a clockwise spiral will tend to self feed as it is used, possibly leading to a wedging action and consequent breakage.
For hand tools, the shank end is usually a square drive, intended for use with the same type of wrench used to turn a tap for the cutting of screw threads.
Drilling followed by reaming generally produces hole geometry and finish that is as close to theoretical perfection as possible.
The absence of any spiral in the flutes restricts them to light usage (minimal material removal per setting) as they have a tendency to chatter.
Other holes, reamed slightly larger in other parts, will fit these pins accurately, but not so tightly as to make disassembly difficult.
After joining the halves, the assembled case may then be line bored (using what is in effect a large diameter reamer), and then disassembled for placement of bearings and other parts.
This type of bolt is commonly used to replace hot peened rivets during the seismic retrofit of structures.
A roughing reamer would have serrations along the flutes to break up the thicker chips produced by the heavier cutting action used for it.
The combination reamer is precision ground into a pattern that resembles the part's multiple internal diameters.
The advantage of using a combination reamer is to reduce the number of turret operations, while more precisely holding depths, internal diameters and concentricity.
This type of reamer consists of a body which, typically, is up to 1/2 inch in diameter, with a rod cross piece at the large end acting to form a handle.
Another name for it is "maintenance reamer", referring to its use in the miscellaneous deburring and enlarging tasks often found in MRO work.
To achieve highly accurate and consistent diameters with a reamer, one must consider process variables that can influence the overall quality of the hole being reamed.
By controlling these variables to the best extent possible, the reaming process can easily produce highly accurate and consistently sized holes.
[4] The continuous use of a coolant stream during the reaming process has been shown to consistently (75% of the time) result in hole sizes that are 0.0001 in.
[5] A properly controlled process is also capable of maintaining a consistent size down the entire length of the hole while minimizing the hour-glass effect.
[6] Like other cutting tools, there are two categories of materials used to build reamers: heat treated and hard.
The most common hard material is tungsten carbide (solid or tipped), but reamers with edges of cubic boron nitride (CBN) or diamond also exist.
[6] The main difference between both categories is that hard materials are usually unaffected by the heat produced by the machining process and may actually benefit from it.
This increases the forces involved in machining and for this reason hard materials are usually not recommended for light machinery.
Heat treated materials, on the other side, are usually much tougher and have no problem holding a sharp edge without chipping under less favourable conditions (like under vibration).
In the United States, ASME has developed the B94.2 Standard, which establishes requirements methods for specifying the classification of reamers.
