Reamers are rotary cutting tools used in metalworking. Reaming is the process of enlarging and sizing a hole by means of a multifluted cutting tool. 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. Non-precision reamers are used for more basic enlargement of holes and light material removal to deburr.
Reaming uses a pre-existing hole in the workpiece and removes a small amount of material called chips. The process involves relative axial and rotational motions between the reamer and the workpiece. It is often done on a drill press, but it may also be done on lathes. The workpiece is held firmly in place by a vise, chuck, or fixture as the reamer is advanced into the workpiece.
A typical reamer consists of a set of parallel or helical cutting edges along the length of a cylindrical body. Each cutting edge is ground at a slight angle with an undercut below the cutting edge. Reamers should only be used to remove small amounts of material to ensure a long life for the reamer and a superior finish to the hole.
There are several variables that determine a reamer's performance: speeds, feeds, and material of the workpiece
The speed depends on the material, as seen in the chart below.
- A starting point for establishing feed rate would be .0025" to .003" per flute per revolution.
Reamer flutes are located at the front of the device as seen in the image above. Small chips are removed by flowing along flutes in the reamer. Flutes can be divided into two general categories: straight and helix. Helix can be further divided into four variations: right hand, left hand, slow, and fast.
Straight fluted reamers are used for general purposes for a wide variety of materials and applications. The length will depend on the application. The entry end will have a slight taper. This produces a self-centering action as it enters the hole, while the larger part of the flute will be of a constant diameter to make the enlargement.
Right hand spiraled reamers have the tendency to pull chips and coolant out of the hole; therefore a right hand style of helix should never be used on a tapered reamer or the reamer may wedge, leading to catastrophic tool failure.
Left hand spiral reamers have the tendency to push chips and coolant in front of the cut, pushing coolant into the hole and the reamer back out of the hole. A left hand spiral can be used on tapered reamers to help prevent grabbing and binding. They should not be used in a blind hole application, because the chips will pack into the bottom of the hole and prevent the reamer from attaining full cut depth.
When selecting a flute, there are four important specifications to consider: flute diameter and length, pilot diameter and length, number of flutes, and flute depth.
A shank is the shaft or stem of the reamer. It is located opposite the flute. When selecting a shank, there are four important specifications to consider: diameter, type, hardness, and one or two piece construction.
Hand vs. Machine
A hand reamer is intended for manual reaming and is typically equipped with a handle. It is designed with a longer taper or lead in at the front than a machine reamer to compensate for the difficulty of starting a hole by hand power along. It also allows the reamer to start straight and reduces the risk of breakage.
Machine reamers have a small lead in and spiral flutes have an advantage of clearing the swarf automatically. The reamer and the work piece are pre-aligned, removing the risk of the reamer going off course. The constant force of the machine ensures that the cutting starts immediately.
There are many options for specialty reamers. The more common types of reamers include chucking reamers which typically come with a straight shank and are used for general purpose reaming, car reamers meant for heavy-duty structural work, and repair reamers which are commonly used in utility and maintenance applications.
High speed steel is most commonly used because it is relatively inexpensive and works well on most materials. However, many other materials are used to make reamers such as carbide and high cobalt alloy steel. Carbide is more expensive than high speed steel but it will outlast it 10 to one when reaming steel. High cobalt alloy steel is used to ream titanium and stainless steel but it is the most expensive option.
The material of the workpiece will determine which cutting fluid must be used to preserve the life of the reamer. Soluble oil can be used for aluminum, brass, stainless steel, and mild steel. Cold air can be used when reaming cast iron and synthetic oil can be used with aluminum and plastics.
There are several standards reamers must follow to ensure proper design and functionality. ASME B94.2 covers the American National Standard for reamers - nomenclature, definitions, types, sizes, and tolerances. BS 122-1 describes the specification for milling cutters and reamers while DIN 1896 discusses machine reamers for metric tapers. Many other standards for reamers can be found in the Engineering360 Standards Library.