As a general rule of thumb you are correct but there are many exceptions to that rule like material and depth which might require a larger and normal hole to prevent tap breakage.
On 1/23/2016 7:48 AM, Peter Blodow wrote: > Erik, > the drill sizes you are using are all 0.2 to 0.4 mm too large, > especially with the small values M2 to M6 where it hurts the most. The > resulting theads have got to be too loose, easy to overtighten. Don't > use complicated formulas, especially not percent calculatations in > public, as my math professor said, just subtract the pitch from the > diameter and you are on line. > Peter > > > > Am 23.01.2016 13:31, schrieb Erik Christiansen: > > This is what I use: > > ---------------------------------------------------- > Metric Coarse | BS 4168 Clearance hole: > | | Type of fit: > Size Drill E Core | Close Medium Free > ---------------------------------------------------- > M2 1.70 61% 1.51 | > M2.5 2.15 63% 1.95 | WARNING: > M3 2.60 65% 2.39 | 3.2 3.4 3.6 2.5mm drill -> 82%. > M4 3.40 70% 3.14 | 4.3 4.5 4.8 > M5 4.40 61% 4.02 | 5.3 5.5 5.8 With a nut length of > M6 5.20 65% 4.70 | 6.4 6.6 7.0 1.5 * diameter, 50% > M8 6.90 72% 6.47 | 8.4 9.0 10.0 engagement is stronger > M10 8.70 71% 8.16 | 10.5 11.0 12.0 than the external > thread. > M12 10.50 70% 9.85 | 13.0 14.0 15.0 > M16 14.25 71% 13.55 | For CI and thin sheet, > -------------------------------------------------- stick near 75%. > > Or in general: # d is full thread depth. > Drill Size = OD - (E*2d) # E is e.g. 0.65 > # d = kP , where P is thread pitch. > > Or transposed for E: E = (OD - Drill_Size)/2d > > k is: ISO Metric > 0.613 > UNF/UNC > 0.613 > # British Association BA > 0.600 > # BSW, BSF, ME (32 & 40 TPI), Whitworth forms > 0.640 > # BSB, and BSP parallel. > > ---------------------------------------- > > So for M12 x 1.5: > > d = 0.613 * 1.5 = 0.9195 > E = (12 - 10.5)/(2 * 0.9195) = 81.5% > > That's too much, especially for a deep hole. The 10.7 mm hole: > > E = (12 - 10.7)/(2 * 0.9195) = 70.6% > > would give Tom's spindle a fair chance. > > (In my previous post, I forgot that the above table is for Metric > Coarse, i.e. 1.75 mm pitch @ M12. :-( > > What would Andy's 10.2 mm hole give with M12 x 1.75?: > > d = 0.613 * 1.75 = 1.07275 > E = (12 - 10.2)/(2 * 1.07275) = 84% > > That's hard on the tap and spindle. Much better is: > > E = (12 - 10.5)/(2 * 1.07275) = 70% > > Erik > > ------------------------------------------------------------------------------ > 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 > > > > --- > Diese E-Mail wurde von Avast Antivirus-Software auf Viren geprüft. > http://www.avast.com > > > ------------------------------------------------------------------------------ > 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 ------------------------------------------------------------------------------ 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
