![]() ![]() ![]() Other advantages of using a larger drill size include improved drill life, straighter holes, and higher feed rates to break up chips more effectively.īecause a roll-form tap displaces material, some material will be forced ahead of the tap and back toward the mouth of the hole, creating a small burr. Because a larger-diameter drill is used for hole preparation, it is stiffer and less likely to bend and break. There are drill charts available in wire gage, machine screw, fractional inch, and metric sizes for most roll-form taps. The material flows down the flanks of the tap threads, creating the actual 60° included angle for the thread. The lobes are smaller in diameter at the front taper portion of the tap and gradually increase in diameter until they are the diameter of the thread to be produced. As the tap enters the hole, the material is pushed by the taper threads at the point of the tap and the lobes on the crests of the tap threads (Figure 3). That’s because the material being tapped is not cut but displaced. Lobes and relief on roll-form tap.įor roll-form tapping, the hole diameter must be larger than it would be for a cutting tap. Today’s roll-form taps achieve consistent tapping performance when proper consideration is given to preparing the hole, selecting the tapping fluid, evaluating the tapping equipment, and choosing the correct tap design.įigure 3. The controlled taper point grind, improved relief, and lubrication grooves have helped overcome the problems with the original design by lowering torque requirements, eliminating burrs, and reducing heat. A controlled minor diameter on the tap can also be maintained so that the crater at the crest of the thread produced by the tap is barely noticeable. Currently, roll-form taps with both plug and bottom tapered threads are produced on precision thread-grinding machines capable of accurately maintaining a controlled taper point, lead, thread form, pitch diameter, and relief (Figure 2). Previously, it was difficult for the tooling on thread-grinding machines to generate the types of relief and configurations of lobes on the taps. Before improvements were made, extreme tapping torque was required, massive burrs were produced at the top of the hole, and excessively high heat was generated during roll-form tapping. In the past, these advantages over cutting taps may have been overshadowed by problems with the original roll-form tap design. For these applications, the potential benefits of using roll-form taps over cutting taps include longer tap life lower cost per tapped hole no chip production, which eliminates the cost and time needed for chip disposal the ability to operate at increased speeds, which improves productivity reduced tap breakage and the production of threads with superior finish and strength (Figure 1). While conventional cutting taps may be preferred for short production runs and very thin-sheet stock parts, roll-form tapping technology may provide a great many benefits for shops involved in long production runs and deep-hole tapping applications. Outdated perceptions have made many machining firms wary of roll-form tapping. Roll-form taps are gaining popularity for producing high-quality internal threads quickly and cost-efficiently.įigure 1. ![]()
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