The subland drill is capable of drilling more than one diameter. There are a variety of drill styles that each serve a different purpose.

In deciding which drill(s) to use it is important to consider the task at hand and evaluate which drill would best accomplish the task. Application of these fluids is usually done by flooding the workpiece with coolant and lubricant or by applying a spray mist. Finish cuts will generate surfaces near 32 microinches, and roughing will be near 500 microinches.Ĭutting fluid is commonly used to cool the drill bit, increase tool life, increase speeds and feeds, increase the surface finish, and aid in ejecting chips. Surface finish produced by drilling may range from 32 to 500 microinches.

Constraining the position of the drill bit using a drill jig with drill bushings.

Spot facing, which is machining a certain area on a casting or forging to establish an accurately located face on an otherwise rough surface.

Casting, molding, or forging a mark into the workpiece.

Establishing a centering mark or feature before drilling, such as by:.

The tendency to walk is also preempted in various other ways, which include: The higher the length-to-diameter ratio of the drill bit, the greater the tendency to walk. This minimizes the drill bit's tendency to 'walk', that is, to be deflected from the intended center-line of the bore, causing the hole to be misplaced. When possible drilled holes should be located perpendicular to the workpiece surface. The type of chips formed can be an indicator of the machinability of the material, with long chips suggesting good material machinability. Chips may form long spirals or small flakes, depending on the material, and process parameters. This causes the workpiece to become more susceptible to corrosion and crack propagation at the stressed surface.Ī finish operation may be done to avoid these detrimental conditions.įor fluted drill bits, any chips are removed via the flutes. ĭrilling may affect the mechanical properties of the workpiece by creating low residual stresses around the hole opening and a very thin layer of highly stressed and disturbed material on the newly formed surface.

Also, the inside of the hole usually has helical feed marks. Drilled holes are characterized by their sharp edge on the entrance side and the presence of burrs on the exit side (unless they have been removed).

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