I need some advice rigid tapping on an Emco120p lathe. The lathe has a 3.5HP motor that can go from 50-3000rpm. It can travel at about 120 ipm (maybe 150 ipm, but haven’t verified it’s max yet). Spindle torque drops off as I go down in lower rpm range, of course. I have done some tapping of aluminum (mostly) and not very deep, say 0.5” or less, and I usually do that at about 300 rpm successfully. However, I am now threading some brass to about 0.75” deep with a substantial M12 1.5 tap (6H, semi-bottoming, spiral flute) and have some problems. I am using a 10.5mm initial hole in the part. When I ran my first attempt at 300 rpm the tap went in, perhaps to full depth, and then stalled. I had quick reflexes (easier at 300rpm!) and was able to stop it in order not to break the tap or drag the part out of the collet or both. I then backed the tap out by hand. I solved immediate problem by “peck-tapping”. I tap to final depth by stepping down 1/8” at a time. This seems to work fine, I have a spindle encoder of course, and so spindle and movement are coordinated in order to to multiple entries on the exactly the same start point. Nice thing about pecking is that I can clear the chips off the tap and spray in some lubricant between each pass. Is there anything “wrong” with peck tapping?
However, I often see videos of machining centers just spinning way a high speed tapping like it’s no big deal. Should I be tapping at much higher spindle speed in order to have more torque? Will the spindle be able to stop and reverse at those speeds to pull it off? I have aggressive start/stop settings on the VFD that controls the spindle, the encoder is 1024ppr quadrature…. IPM = RPM X pitch(mm) X 0.03937 so at 2000rpm it would be moving at 118 IPM, within it’s capability. Or at 1500rpm it would be 89 IPM. I would like to not break my $30 M12 tap so have been afraid to just go for it, but wondering what a real machinist would do? I am not one. :-) -Tom ------------------------------------------------------------------------------ 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
