Square Hole Drilling Machine and Its Working Principle
Removal of material in electrical discharge machining that includes the generation of debris in the working space, comprises eroded substances with electrode particles and by-products of dielectric decomposition.
Gap contamination of a certain threshold that is uniformly distributed is desirable in the interest of discharge. However, excessive debris concentration confined to isolated domains in the gap because of insufficient flushing leads to repeated localization of the discharge in a particular location.
The whole machining process could have significant effects on the strength, stability, geometry, and integrity of the finished parts. Based on that, adequate gap flushing is very important in terms of both machining productivity and the quality of the machining surface.
The gap can be flushed using the forced flow of the dielectric fluids through holes in the tool, however, the idea could leave a footprint on the machined surface since the work shape produced in EDM is complementary to that of the tool. Another means of carrying out flushing is through micro holes fabricated in the tool for that purpose.
In a situation where it is impossible to provide flushing holes in either of the electrodes, the dielectric could be directed and controlled at the gap in the form of a jet from outside the machining area. That could be an ineffective technique when machining depth or the frontal machining area is large.
Generally, holes are parts of the machining process and could be found directly or indirectly on every machined surface. The hole could be square, round, rectangular, and any other possible shape based on part geometry and designs.
The machines for making round holes are common in the market, but such is not the case for squares and other types of holes.
The methods in use currently for making such holes (square and others) are broaching, electrode-discharge machine (E.D.M), and electro-chemical machine.
However, these machining methods are very expensive and may not be affordable for every manufacturer or fabricator. Besides, they also need special skills and a high level of professionalism.
Using the principle of the Reuleaux triangle discovered by a German engineer Franz Reuleaux, a new model of a square hole drilling machine has evolved to make the operation simpler and cheaper.
The principle is one example of a wide class of geometrical discovery. It discussed the famous curvy triangle that had been used in various mechanisms such as the Watts Brother tool.
Franz Reuleaux was not the first to draw and consider the shape formed from the intersection of three circles at the corners of an equilateral triangle, because the use of the curve and its special properties for producing polygonal holes was given by Sir James Watts in 1914.
Since then, geometry has been evolving from day to day producing the exact square which it evolves.
The mechanical design of the square hole drilling machine is based on the Reuleaux triangle principle. The concept was to evaluate how the circular motion can be converted into a square motion using a linkage mechanism. The idea leads to the construction special tool that drills the exact square holes.
In order to make the machine operate like a rotating tool such as a drill press, a force is used to make the Reuleaux triangle rotate inside a square, such requires a square guide to constrain the triangle and special coupling to describe the center of rotation as it moves within the constrain.
The importance of the design is that the driving end can be placed in a standard drill press; the other end is restricted to stay in the fixed square that will yield a perfectly squared locus and could be turned into a working square to drill a hole.
The working principle of the square drilling machine is based on the transformation of the rotating motion of a shaft about its axis to revolving motion around the same axis in a given profile.
The profile is confined by four governing ellipses at each corner. With their center at the vertices of confining square, it will guide the tool in a confined profile keeping the rotation intact.
The above principle will lead to the cutting of the square geometry as required, since revolution becomes an integral part, the Reuleaux triangle center is not fixed and it has to be moved in a profile which is made by those four ellipses.
The principle makes it possible to put the components together without compromising the working of each component.
The following are the components that make up the integral parts of the machine;
Drilling unit: this section provides the impact drill force required for the operation. In its arrangement, the end of the universal joint is connected to the tool holder of the drilling machine. The spindle speed is made to be constant for all operations but its cutting speed varies all along the cutting edge.
The outside diameter is one factor used in determining the cutting speed. At the center of the chisel edge and on the lip the cutting speed is zero. The change of speed is proportional to the radius at any point, such is an important factor in any drilling operation.
Universal Joint: the universal joint connects two shafts at an angle for the purpose of transmitting torque.
While the center of the Reuleaux Triangle rotates itself and revolves in a noncircular path using the universal joint, the Reuleaux triangle can revolve in a noncircular path perfectly. It makes it easy for coupling or joint to transmit rotating power using a shaft in any direction.
Some coupling in a rigid rod allows the rod to bend in any direction. Therefore, it is the most used in a situation that requires shafts to transmit rotary motion.
The universal joint is not a constant-velocity joint, rather, it is made up of a pair of hinges located close together, oriented at 90 degrees to each other, and connected by a cross shaft.
3-Point Cutting tool: it is made up of EN36, a material with high hardness and strength. It is a special tool usually mounted on the Reuleaux triangle and has 3-cutting edges in order to obtain the square hole.
While in operation, the tool requires pre-drilling to reduce wear on it and the amount of swarf to be removed. The idea prolongs its life span and reduces its pressure during operation.
Supporting member: one of the supporting members of the machine is the square guide. It is a stationary component that guides the Reuleaux triangle to move in a square shape and to rotate in a fixed plane.
The square guide is usually connected to the drilling unit using two steel rods and clamped to the drilling unit with clampers. Suitable clampers will provide support to the portable drilling tools.
To ensure the rotation of the tool without jamming inside the square hole, the square hole will be larger than the width of the Reuleaux triangle, such ensures smooth running operations.
