On Sunday 04 January 2009, Roger wrote: >Gene Heskett <gene.hesk...@...> writes: >> On Sunday 04 January 2009, Roger wrote: >> >Stephen Wille Padnos <spad...@...> writes: > >snip > >> Don't forget that a lost step is actually a full step, not whatever >> microstepping might be setup in the driver. But one lost full step is a >> never happens scenario, cuz if it loses a step, it is stopped and then the >> whole acelleration curve must be repeated in order to prevent its simply >> locking in place. >> >> It is a nice idea, but the part of actually making it work is pretty >> complex. > >Gene, >I'm not sure that you can assume that the table is stalled if you loose > steps. Old timers who used to run stepper driven Bridgeports have told me > that leaning on the table could cause the machine to loose steps. It didn't > stop the machine, the axis kept running, the part dimensions just came out > wrong. > >Roger
So have I, but something like that is the exception to the rule. The motors torque was exceeded, yes, but it wasn't moving that fast so it could keep on running. To me that would be a sign telling me I needed bigger motors and drivers. While a bridgeport can be moved with small motors like I use, when handling the size of a bridgeport tables weight, I'd want nema 34 motors and 80 volt drives as absolute minimums. My x table only weighs maybe 20 pounds, the bridgepoort closer to 200. My problem with the higher rapids on my micromill is that the ways are so short, when the table is at the extremes of it travel, the gib binding can stall mine when its only doing 5 ipm, whereas slightly to the left of center so the motor is about in balance, I can do 25 ipm. One of the reasons I'd like to build a gantry style machine is that the frictional effects are about the same over the whole work envelope. This short gib problem is much of the reasons I built a whole new z drive for it, the original design couldn't push a 1/16" drill bit in alu even using the peck cycles. The new one can put 150 pounds on a 1/2" bit, nice but little use when the spindle is so puny powered (400 watt motor, but the vsd can only do 225 before the fuse clears), but it did allow me to make a new output air manifold for my air comnpressor last week, to replace the cheap and old age cracked pot metal one that came on it. You can see the mess of my shop and that mill at <http://gene.homelinux.net:85/gene/emc> if you haven't seen it before. Redneck engineered if there ever was such a category. :) Having replaced the hexfet in the vsd (it blew when the fuse didn't and old computer psu's are full of better hexfets than that one ever was), I could probably up the fuse size to 3.15 amps from 2, and that would help. That would certainly put those nylon gears on notice though. :( But having to rebuild that would be a good excuse to make it spin faster too, something it needs to do anyway. The gear shift should have been 4 or 5 to 1, its 2 to 1 now. -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) "I'd love to go out with you, but I want to spend more time with my blender." ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
