On Saturday 23 January 2016 12:08:47 andy pugh wrote: > On 23 January 2016 at 16:53, Gene Heskett <ghesk...@wdtv.com> wrote: > > Does that not give a 100% thread? I was under the impression we use > > a .85 multiplier. > > The idealised depth of thread for a perfectly sharp 60 degree thread > with no rounding or flats is: > (pitch/2) * tan(60) = 0.866p > The core size of the thread is this D - 2 * 0.866p = D - 1.72p > However: There is an H/4 flat on the internal thread, so the real > thread core is D - 1.22p > > If you drill a hole of D-1p then you are at about 78% engagement. > > https://en.wikipedia.org/wiki/ISO_metric_screw_thread
Now we are getting more precise than we can drill with the typical drill bit, which usually drills oversize because the tip flats are un-avoidably off center. Even to a small extent for pricy carbide bits in the smaller sizes. Yesterdays finished tapping looked great, but I think I could have used the next larger #drill. Yeah, my back of a napkin said a .089 drill, kcalc says 0.0984251968503937008 for a 3mm.5 screw. No wonder I felt like I should peck it, the hole WAS too small. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Site24x7 APM Insight: Get Deep Visibility into Application Performance APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month Monitor end-to-end web transactions and take corrective actions now Troubleshoot faster and improve end-user experience. Signup Now! http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
