On Friday 22 January 2016 10:58:13 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? > Nope, done it quite a few times myself, usually at about 1/4 turn pecks because I can't hold a tap any tighter with my rube goldberg tap carrier. Even if it dulls the tap faster, its cheaper than starting all over to make the part. And I usually blow it clean & glop on some more buttercutt while its backed out of the hole too. But I think I may have solved the tap slippage, I stumbled over an Irwin (spit, pissy taps IMO) metric tap kit at Lowes last night, that had a small tap handle, which if I can drive the handle out of it, and turn its butt end to fit my boring bar holder, will hold a tap better than the drill chuck on a rod stuck in the boring bar will do.
Or stuck in one of those chinese er32 adapters, fixes the same problem on the G0704. One of the things I'll check today while being buried in snow as I am trying to make a camera mount screwed to the bottom face of my home-made spindle lock. Change of subject: Neither of the 3 pieces for that high speed spindle have arrived yet, despite being here in the states. I believe that 80mm diameter will be a problem. Unless I can cobble up a quick change to replace the existing spindle cartridge with it, but that won't dis-mount the existing motor, getting rid of its weight. I also have visions of pinning the existing head so I could slap it back on without an hour spent tramming it, and ordering another head casting as a part, which would make changing it a 4 nuts/washers and a small hoist job. Endless possibility's occupy my "downtime" ... :) > 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 Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ 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
