On 24.01.16 14:16, tom-...@bgp.nu wrote: > OSG, referenced earlier by John Thornton, has this tool > (http://www.osgtool.com/Technical.asp?tid=1&id=1) that calculates hole > size given Major Dia, Pitch, and Engagement (% of Thread). Their > numbers seem to be slightly different than Erik’s though, but they > suggest 60-70% engagement for deep hole tapping.
It agrees generally, then. But we need to understand the difference in the decimals. The OSG calculator's internals are unknown, so we need to use its behaviour to theorise on where it goes wrong. > For example: > > > On Jan 23, 2016, at 7:31 AM, Erik Christiansen <dva...@internode.on.net> > > wrote: > > > > 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. > > > > ---------------------------------------- Your observation that the OSG calculator differs a bit made me check the value of k = 0.613 for ISO Metric. https://en.wikipedia.org/wiki/ISO_metric_screw_thread says it is 0.614. That insignificant bit of rounding difference doesn't explain anything, though. > > 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. > > The OSG tool gives 10.7mm at 66% engagement (for 12mm 1.5). Looking for clues here: The ratio of the results, 66/70.6 = 0.93, which is near as damnit 0.92, so if we dumb down the formula I use, to omit thread height/pitch correction: E ~ (12 - 10.7)/2 = 0.65 we are off almost exactly as much as the OSG calculator. (Well within rounding tolerance for display purposes in a web app.) It may be that the imprecision is deliberate. The OSG page says "Drills generally cut holes larger than their diameters. In the form bellow, the probable percentages of full thread were determined by the average amount oversize the various drills are expected to cut." We have no way of knowing what a black box on the internet is doing. I think I'll stick with a visible calculation, so that I have an understanding of where the value comes from. Whether it's accidentally or deliberately inaccurate, the OSG calculator can't know when I'm using a reamer, or a dowel drill: Drilling Accurate Sized Holes: Grind matched 0.4 - 0.8 mm radii on the cutting wings (corners) of a new or good quality drill. Ensure the radii are even, and have clearance, so the drill will cut easily. This forms a dowel drill, used by toolmakers. Drill 0.3 mm undersize first. Run the dowel drill 30% faster, and feed quickly, using cutting fluid. (AME 90:45) 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
