NOTE: If tapping idfficult to machine materials or using small taps, use a lower thread percentage such as 60% to 70%. The UN specification specifies that the common height of a thread should be 5/8 th of this maximum height.ħ5% to 80% thread roughly equals 5/8 th of this maximum height. Thread percentage: (77% thread is what you want to use) A 100% thread is 3/4 qtr, or (6/8 th), of the full 60° triangle which is the maximum allowed height of a full thread, the "V" shape, including flats. NOTE: The tap drill size of a hole that will be cold form tapped is usually bigger than it cutting tap counterpart. These taps have no "flutes" and are usually oval shaped or not quite round. Form tap: (Cold forming tap) A tool that makes the helical portion of a threaded hole by forming, or deforming, the material as it moves along a predrilled hole. They should be used in that order when tapping holes that do not break through. Cutting taps usually have sharp "flutes", somewhat like the spirals of a drill, where the chips can accumulate and be ejected out of the hole NOTE: Cutting taps come in sets of 3 A starter tap, a midway tap, and the bottoming tap. Cutting Tap: A tool that makes the helical portion of a threaded hole by cutting material as it moves along a predrilled hole. NOTE: Most basic sizes have a coarse and a fine series of thread. Pitch: (Distance between each thread, or "V"s.) The distance the a screw or nut will advance every 360° turn. NOTE: If the length of the threaded portion of a screw or threaded hole is shorter or longer than one inch, the size of the "V" shape is still defined by the number of thread that would fit along a one inch length. TPI: (Threads per inch) The number of thread, or "V"s along a one inch length which in turns, defines the size of the "V" shape of the helical portion of a thread. NOTE: The size of the hexagon of a bolt or nut has no relevance when defining a thread size. The biggest external diameter of a Screw or the biggest internal diameter of a threaded hole. Outside diameter: This is the biggest diameter of the helical portion of a thread. NOTE: The American Metric UN thread standard is compatible with the international ISO Making a thread that follow these specifications will ensure that it will work with threaded holes or shafts made by other manufacturers that follow theseĬommon specs. Metric UN: (American Metric Unified National thread form) A standard that describes the shape of an internal or external thread using Imperial UN: (Imperial Unified National thread form) A standard that describes the shape of an internal or external thread using imperial inch dimensions. This is where we publish technical articles, applications stories, tip and tricks, new product announcements and press releases.Glossary TDS: (Tap drill size) The size of the hole that must be drilled before a tapping operation. See below for tap/drill size formulas, and formulas to determine maximum and minimum drill hole sizes for appropriate percent of thread.įorm taps operate most efficiently at spindle speeds 1-1/2 to 2 times faster than those recommended for conventional cutting taps, especially in softer materials and/or with fine pitch forming taps. Allen Benjamin will not guarantee the performance of taps with the shorter chamfer.Įntry diameter, measured at the thread crest nearest the front of the tap, is an appropriate amount smaller than the diameter of the hole drilled for tapping. When a controlled maximum chamfer shorter than 2 threads is required, an additional charge will apply. TTap Drill Sizes for Forming Tapsap Drill Sizes for Forming Taps Tapping Drill And Clearance Hole Sizes For Metric Tap Drill Size by percentages chart. The chamfer on BOTTOM style form taps is approxi mately 2 threads long and requires a drilled hole depth 3-4 pitches beyond the full thread required. Selection Criteria & Wizards Size Chart For Cutting Threads Figure 1: Tap and die set A tap drill chart determines what size hole to drill before tapping female threads and what size pipe is needed for male threads. Industry common suggested thread engagement guidelines: Powdered Metal or Cast Iron 50 - 65. They have been designed to provide consistent torque performance, lower end load and lower thread forming torque. Whenever entry taper length is specified in terms of number of threads, this length is measured in number of pitches (p).īOTTOMING LENGTH = 1-1/2 to 2-1/2 PITCHES Tap-fix ® screws are thread rolling screws with a trilobular shaped body that reduces friction during threadforming in the parent material. Entry taper length is measured on the full diameter of the thread forming lobes and is the axial distance from the entry diameter position to the theoretical intersec tion of tap major diameter and entry taper angle.
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