On 08/13/2013 09:00 AM, Viesturs Lācis wrote: > 2013/8/13 John Thornton <bjt...@gmail.com> > >> When tapping in steel it is only necessary to have %50 thread depth and >> %75 thread depth in soft materials. > > > Do you mean it to have tapped 50% / 75% of hole's depth or do you mean > increasing the initial drill size so that height of actual thread profile > is 50% / 75% of the standard (theoretical) thread profile height? >
From Wikipedia ----------------------- Thread depth Screw threads are almost never made perfectly sharp (no truncation at the crest or root), but instead are truncated, yielding a final thread depth that can be expressed as a fraction of the pitch value. The UTS and ISO standards codify the amount of truncation, including tolerance ranges. A perfectly sharp 60° V-thread will have a depth of thread ("height" from root to crest) equal to .866 of the pitch. This fact is intrinsic to the geometry of an equilateral triangle—a direct result of the basic trigonometric functions. It is independent of measurement units (inch vs mm). However, UTS and ISO threads are not sharp threads. The major and minor diameters delimit truncations on either side of the sharp V, typically about one eighth of the pitch (expressed with the notation 1/8p or .125p), although the actual geometry definition has more variables than that. This means that a full (100%) UTS or ISO thread has a height of around .65p. Threads can be (and often are) truncated a bit more, yielding thread depths of 60% to 75% of the .65p value. This makes the thread-cutting easier (yielding shorter cycle times and longer tap and die life) without a large sacrifice in thread strength. The increased truncation is quantified by the percentage of thread that it leaves in place, where the nominal full thread (where depth is about .65p) is considered 100%. For most applications, 60% to 75% threads are used. To truncate the threads below 100% of nominal, different techniques are used for male and female threads. For male threads, the bar stock is "turned down" somewhat before thread cutting, so that the major diameter is reduced. Likewise, for female threads the stock material is drilled with a slightly larger tap drill, increasing the minor diameter. (The pitch diameter is not affected by these operations, which are only varying the major or minor diameters.) This balancing of truncation versus thread strength is similar to many engineering decisions involving material strength, material cost and weight, and manufacturing cost. Engineers use a number called the safety factor to quantify the increased material thicknesses or other dimension beyond the minimum required for the estimated loads on a mechanical part. Increasing the safety factor generally increases the cost of manufacture and decreases the likelihood of a failure. So the safety factor is often the focus of a business management decision when a mechanical product's cost impacts business performance and failure of the product could jeopardize human life or company reputation. For example, aerospace contractors are particularly rigorous in the analysis and implementation of safety factors, given the incredible damage that failure could do (crashed aircraft or rockets). Material thickness affects not only the cost of manufacture, but also the device's weight and therefore the cost (in fuel) to lift that weight into the sky (or orbit). The cost of failure and the cost of manufacture are both extremely high. Thus the safety factor dramatically impacts company fortunes and is often worth the additional engineering expense required for detailed analysis and implementation. -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/ ------------------------------------------------------------------------------ Get 100% visibility into Java/.NET code with AppDynamics Lite! It's a free troubleshooting tool designed for production. Get down to code-level detail for bottlenecks, with <2% overhead. Download for free and get started troubleshooting in minutes. http://pubads.g.doubleclick.net/gampad/clk?id=48897031&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users