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Applying the proper lubricants in tapping operations can result in longer tap life, increased production, better workpiece size control, smoother and more accurate threads, less resharpening, and more efficient chip removal.
Generally, for best tap performance, straight cutting oil should be used. For non-ferrous and non-metallic materials, a coolant or a cutting fluid (light oil or soluble oil) is recommended.
Often, machining centers are equipped with a coolent of a cutting fluid that contains enough water and oil to provide adequate cooling and lubrication for a variety of tools and workpieces. However, most soluble blends are not suitable for tapping applications. Tapping, especially with thread-forming taps, requires more lubrication than cooling. A coolant or cutting fluid might lack the lubrication necessary to obtain acceptable tool life and part finish. Consult your coolant specialist for recommendations.
After you select the proper lubricant, it is also important to choose the right method of application and pressure. For tapping, use more than one nozzle around the tap. The nozzles should be located as close to the surface of the part as possible, be positioned at an angle close to the axis of the tool, and point directly into the hole to flush chips from the flutes. For horizontal tapping, where the tap is stationary and the workpiece is rotating, consider using two streams of lubricant, one on each side of the tap.
Whether you are tapping vertially, horizontally, or on an angle, make sure the lubricant reaches the cutting lands of the tap at all times, especially at the point or chamfered portion. Brushing or squirting oil or fluid onto the tap does not provide sufficient lubrication. In fact, heavy viscosity oil may cause the chips to "stick" or "cling" to the tap, increasing the chance of breakage. In addition, when the lubricant is automatically applied only on the forward motion of the tap, you should time the application of the lubricant so that it will reach the hole before the tap starts to cut. This applies particularly to machines on which the cutting fluid is automatically shut off during the tap's reversal.
For maximum effectiveness, it is often best to force the lubricant into the hole under pressure. The amount of pressure applied caries depending on the tapping method, hole depth, and tapping speed.
Try to keep tapping lubricants as clean as possible using a filtering system or other equipment. Dust and other foreign particles can contaminate the oil and decrease its effectiveness. Be sure to thoroughly clean machines and oil tanks when adding new lubricant and at regular intervals to ensure optimum tapping results.
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