On 01/22/2016 09:58 AM, tom-...@bgp.nu wrote: > 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?
Nothing wrong with peck tapping. In many cases it lets you replenish lube as you have noticed. Make the first peck fairly deep then go shallower as you go deeper, you should be able to do this in 2 or 3 pecks. > > 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? Faster spindle gives you more HP and inertia > 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…. In Linuxcnc the spindle is commanded forward until the tap gets to the depth called for, as the spindle slows to reverse out the Z axis follows and you get an overrun, the tap is reversed out to the start Z, the spindle is commanded off and the Z continues to overrun up to stop then goes back forward to the initial start point. > > 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. :-) > You can run a tap quite fast in brass as long as the tap is "like new" sharp, a slightly dull tap that will cut steel will bind in the copper alloys and sometimes wedge very tight. I tap 5/8-11 in C1045 steel at 200RPM on my CHNC quite often, M12x1.5 should be a cake walk. Ed. ------------------------------------------------------------------------------ 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
