On 23.01.16 12:27, Gene Heskett wrote: > 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.
Ahem, it was WAAAY too small. ;-) Just a glance at the table upthread shows that 2.6mm (0.102") gives 65% engagement, which is as much as I ever want on M3, to avoid busting the tap. Even kcalc's 2.5mm (0.098") drill is too small, giving a dangerous (to small taps) 82% engagement. And that .089 (2.26mm) gives an engagement of: E = (OD - Drill_Size)/2kp = (3 - 2.26)/(2*0.613*.5) = 120% That has the tap drilling as well as tapping! You did superbly to not break the tap, Gene. I tried a 2.5mm (0.098") drill for M3. Once. Although the tap didn't break, I went straight out and bought a couple of 2.6mm drills. Now I can tap M3 without my hair standing on end. 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
