On Tuesday 11 August 2015 02:48:53 Dave Caroline wrote: > It also depends on minimum tap size, a tiny tap will be less able to > stand any vertical strain due to encoder resolution in thou per > encoder edge and there has to be an amount due to the turn around of > up to something (a count) plus any delay in the software and servo > driver lags (ferror)
I haven't broken a tap (yet). Because the lock between spindle and carriage is beyond my weak drive, even a drive failure from spinning the teeth off the lower drive pulley has only resulted in a howling drive as the PID pours on even more coal. So, I kill the spindle power and finish the job by hand using the chuck key as a handle. The carriage dutifully follows my motion applied to the chuck until I can either have the tap free, or in one event, I hand pecked it for about 10 minutes and finished the job, then backed it out of the hole, intact. Where I get in trouble is on a bigger tap that isn't chucked tightly enough to prevent its turning in the drill chuck mounted to the toolpost. That slippage will get it out of time & put some strain on things, best to loosen the chuck, back it away, pull it off the QC and use a tap wrench to extract it from the unfinished hole. > Rather machine dependent(and its settings) and I doubt anyone can > write a general specification. I can't argue that point. Each machine is its own best judge. With a 50 cycle wheel on the lathe, direction reversals are not a problem as they are detected instantly. At what point a lessor count in the wheel would become a problem I don't know. An 8 slot wheel feeding an ABX encoder might work surprisingly well. > I wonder if the tap makers have any numbers for machine taps. > > Dave Caroline > > On 11/08/2015, Jon Elson <[email protected]> wrote: > > On 08/10/2015 06:38 PM, David Bagby wrote: > >> Hi, > >> I'm planning a mill conversion to LCNC and I'd like it to be able > >> to do rigid tapping. > >> > >> I figure that this will require an encoder or equivalent) on the > >> spindle. I won't be able to to easily attach a common encoder disc > >> to the spindle, so I will probably have to create an encoder (which > >> appears easier than doing a remote encoder driven via a belt etc). > >> > >> I've looked but not found a spec for the required encoder > >> resolution. Does anyone have advice as to min spindle encoder > >> resolution (ppr) required? > >> Has anyone gotten by with 8 or 12 pulses (32 or 48 quadrature) ? > > > > I've been doing it using the 81 tooth bull gear on my > > Bridgeport 1J head, and that works fine. That comes out to > > 324 quadrature counts/rev. I'd guess that your counts will > > likely work OK, too. You can figure out the steps/second the > > encoder value will show. For instance, at 100 RPM, the > > spindle will be turning 1.667 RPS, and 32 counts/rev will > > give 32 * 1.667 = 53.33 increments/second to the encoder > > value. Most machine controls don't have the bandwidth to > > keep up with that, and will just average over it. > > > > The worst situation would be that this would feed a > > stairstep position to the PID (assuming a servo Z axis) and > > that the PID + drive combination would have some resonance > > at certain frequencies that could be excited by the stairstep. > > > > Jon > > > > -------------------------------------------------------------------- > >---------- _______________________________________________ > > Emc-users mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > > ---------------------------------------------------------------------- >-------- _______________________________________________ > Emc-users mailing list > [email protected] > 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> ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
