The Reamed

reaming process with which holes are enlarged
File source: http://commons.wikimedia.org/wiki/File:ReamerMachineSpiral.jpg

Reaming is a chip removal process with which you want to enlarge a hole and achieve a certain surface finish and certain dimensional tolerances. So it is a finish of the holes that are made in the reamer.

El reamer is a tool similar to a drill, to which we tell it to make two movements, one of rotation on its axis and another of rectilinear movement along the axis.

We can carry out the finishes with a machine tool or manually.

Reaming should be done at low cutting speeds. A very small amount of material is to be removed.

The spiral can be clockwise or counterclockwise, depending on use. For example, a conical hand reamer with a clockwise spiral will tend to self-feed as it is used, possibly leading to a wedging action and subsequent breakage. Therefore, a counterclockwise spiral is preferred even though the reamer continues to rotate clockwise.

Reamers are cylindrical tools that have longitudinal, straight or helical grooves and teeth carved, on which the following areas can be distinguished:

  • A handle, for attachment to the machine
  • A joining neck
  • A body or tool that removes material. In turn, within this body, several areas are distinguished:
    • Chamfer. The start chamfer located at the end of the tool and is the area where the cut occurs. The value of the angle of this chamfer depends fundamentally on the material to be machined and the reaming method to be used, manual or automatic, using smaller angles for the manual method and soft materials, due to the decrease in the necessary axial force.
    • Initial cone. It is the conical part adjacent to the chamfer where a very small chip removal occurs. As a consequence, chips in reaming are torn off in the radial direction, as opposed to drilling, where they are torn off in the axial direction.
    • Sizing area. It is the next cylindrical area where the hole is finished with its dimensions and surface finish. In this area there is no actual chip removal and the cutting edges rub against the surface of the hole
    • Final cone. It is the final conical area whose mission is to reduce the friction of the tool with the hole and prevent it from overheating.

If a transverse cut is made on a reamer, it can be seen how the grooves that it has carved give rise to cutting edges that have their detachment and incidence face. The number of edges or teeth varies and is usually always greater than two. It can also be seen that the rake angles used in the reamers are positive.

Tool materials

Like other cutting tools, There are two categories of materials used to build reamers: heat treated and hard. Heat treated materials are composed of different steels, in particular simple carbon (unalloyed, considered obsolete today) and high speed steels. The most common hard material is tungsten carbide (solid or pointed), but reamers with cubic boron nitride (CBN) or diamond edges are also available.

The main difference between the two categories is that hard materials are not usually affected by the heat produced by the machining process and can really benefit from it. The downside is that they are often very brittle, requiring slightly blunt cutting edges to avoid fracture. This increases the forces involved in machining and for this reason hard materials are generally not recommended for light machinery. Heat-treated materials, on the other hand, tend to be much stronger and have no problem maintaining a sharp edge without chipping under less favorable conditions (such as vibration). This makes them suitable for hand tools and light machines.

Lubrication

During the reaming process, friction causes the part and tool to heat up. Proper lubrication cools the tool, increasing its life. Another benefit of lubrication includes higher cutting speeds. This shortens production times. Lubrication also removes chips and contributes to a better finish on the workpiece. Mineral oils, synthetic oils, and water-soluble oils are used for lubrication and are applied by flooding or spraying. For some materials, only cool air is needed to cool the workpiece. This is applied by means of an air jet or a vortex tube.

Types of reamers

types of reamers
Copyright - 2005 - Glenn McKechnie

There are different types of reamers, the main ones being the following:

Cylindrical Fixed Reamers

The cylindrical fixed reamers they are integral tools that are used to calibrate and finish holes, eliminating a very small thickness of material. Those with a small diameter are built integral with a conical or cylindrical handle for their coupling, and those with a larger diameter are built with holes and grooves for the transmission of movement. The teeth of these reamers can be straight or helical, and in the latter case, the helixes can be right or left. For soft materials, left-hand propellers are used to prevent them from getting into the material, while for hard materials, right-hand propellers are used to facilitate penetration. These tools are normally made of high-speed steel, and there are also some in which the cutting edges are made up of welded carbide inserts.

Tapered Fixed Reamers

Conical Fixed Reamers are used for machining and finishing of conical holes, existing conical roughing reamers with straight edges equipped with chip breaker grooves, and conical finishing reamers with straight or helical edges

Expandable Reamers

They are fixed reamers that have three or four longitudinal grooves that allow widen them by the action of a conical screw, achieving small variations in diameter. This widening is carried out when the tool has worn out, with which it can be rectified, and therefore, increase its life. This type of reamer is used for very abrasive materials, which cause great wear on the tool, and in no case to vary the dimensions of the hole. The finishes and tolerances that can be obtained with them are worse, also presenting the disadvantage of being weakened at the end where the efforts are greater.

Adjustable reamers

Adjustable reamers are made up of blades made of high-speed steel or carbide, supported on a frusto-conical base that move in the radial direction when displacing said body by means of the action of a screw, thus varying their diameter. This type of reamers, due to the blades, have straight teeth.

Fonts

  • Manufacturing processes. José Domingo Zamanillo Cantolla, Pedro Rosado Castellano
  • Manufacturing Processes Reference Guide. Todd, Robert H .; Allen, Dell K .; Alting, Leo (1994)
  • https://en.wikipedia.org/wiki/Reamer