Drilling deep hole is not only the "unique skill" of gun drill and integral solid carbide burs. As early as 15 years ago, the united machinery and engineering corporation (AMEC) began making its Guided t-a bit (to perfect its t-a drilling system) and used it for gun drilling. The Guided T-A bit is A customized tool designed for customers' specific processing needs, which can process long diameters of 5, 10, 28 or larger. It consists of a high strength steel blade and precision grinding of cutter holder on the form, the knife can be clamped on the company's standard series of cemented carbide and high speed steel blade, the processing aperture range of 9.5-115 - mm (can be customized size). The drill can be used for milling machine or lathe.

In addition, the design of the Guided t-a bit enables it to overcome the difficulties which may result in the failure of the solid carbide burs. Miller added, "the solid carbide drill bit is not suitable for intermittent cutting, such as drilling cross-hole or exporting holes in the surface or inclined plane. Usually, in the case of these machining situations, the hard alloy bits have a large force on one side, so it is easy to cause the drill to deviate from the center line or fracture. The Guided T-A bit has A supporting area behind the flat drill at the front, and the supporting area always keeps in contact with the hole being processed and does not allow the bit to deflect. AMEC company advised, the user can use A first length is relatively short (1-2 times the diameter) of pilot drill processing guide hole, its aperture and Guided T - A bit diameter is the same, this helps to reduce the bit offset and oscillation process.

Three years ago, Smith International Inc., A supplier of U.S. oil and natural gas, tried using A Guided t-a bit to finish the process of drilling in high-speed steel. Processing tasks included in 4140 on the steel tube heat treatment (hardness HRC30-32) at 30 degrees oblique hole drilling depth is 355 mm. According to Ray Stafford, a processing manager at the company, it takes about five hours for each hole to be used by workers before they are drilled through a high-speed steel drill. "We first work out a guide hole with a fixed core drill, then use a high speed steel extension taper shank drill to get to the drill hole, and then use the drill to drill through the hole. Therefore, we hope to have a bit that can improve the processing speed."

The Smith company asked AMEC to make A Guided t-a drill with A diameter of 44.45mm and A length of 355mm. "We got a bit of the required specification," Stafford said. "it worked very well after it was put into use." The deep hole is processed from beginning to end using only one drill. The processing time of each hole is only 1 hour and 15 minutes. In addition, once used to drill the drill, every three holes must be resharpened. The Guided T-A drill can process 9 holes before it has to replace the high speed steel blades. Now, the company has found that it can also be used in more processing situations.

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