On Wednesday 13 January 2016 11:34:04 andy pugh wrote: > On 13 January 2016 at 16:09, Rick Lair <[email protected]> wrote: > > I have never dealt with stepper motors/drives and one of the guys at > > our shop is kicking around converting and old 9x30 Southbend lathe > > to cnc using Linuxcnc > > My Chinese 9x30 is OK on the X with a 2.5Nm stepepr but a bit weak on > the Z with a 3.5Nm stepper. > > If I was converting a lathe using steppers (and I am not, I am > converting using servos) then I think I would be looking at the > new-fangled closed-loop steppers. > > For Z probably: > http://www.ebay.com/itm/121787201520
Thats a decent price for an integrated unit. I used a 470 oz/in nema 23 on my Z, mounted on the left, sticking out of the change gear cover, and made miniature taperlock hubs for 2 of the old change gears, which I had converted to metal versions, one to put the 40 toother on the motor shaft, and one to put the 80 toother on the end of the ball screw, so my Z is geared 2/1. And with a 16x5 screw, can still move 60+ ipm. > And something a bit shorter in the hope if tucking it back underneath > the saddle for X > http://www.ebay.com/itm/111796968667 I did put a piece of a ball screw in the X, more to get efficiency of power transfer than for the precision, but with no room under the front after I had made a replacement apron to meet up with the ball screws nut flange, I extended the rear of the carriage with an alu block, first putting an oddball nominally 50 oz motor directly on the rear of the screw, but was forced to redo it a bit and put another of the way too heavy 470's on it because the 50 just didn't have the cajones to do the job. It was being pushed back by the cutting forces. That extra weight is just enough to unload the front v-way, so the gibs had to be snugged up till the z screw was having a hard time moving it. In retrospect, a set of reduction gears between the smaller motor and the oem screw would probably have been a better idea as that would have allowed the motor to be raised out of the way above the workpiece, and turned around to put its weight over the saddle by a shielded belt drive on the rear, even the weight of the triple stack 470 would have been much less of a problem, and that alone would have contributed to the x accuracy by reducing the tendency for the V-way to be lifted. I may even do that eventually, but thats just changing the color of the lipstick on this pig. I relate this not as a do recommendation, but more as a don't do like I did. My way does have x accuracy problems because of this has a tendency for the z screw to pull the carriage, exerting a bit of rotation looking down at it from above, lifting it very slightly on the V-way, changing the x about 2 or 3 thou when it does. That however seems to be slowly wearing in, and less of a problem as time goes by. Caused by haveing the rear gib snugged up to prevent lift, tipping the tool away from the work when turning OD. I fact, now that I have done it, I don't recommend doing it to any of the 7xnn series lathes, one should just get a machine thats big enough to carry the weight involved in the first place. Carriage footprint on the way's is very important, and the 7x lathes just don't have enough to be effective. Hindsight is always better in my observations. Like putting lipstick on a pig, my 7x12 is still a pig. :) > That is just an indication of what I am talking about, not in any way > a recommendation of manufacturer or supplier. > > Squeezing a ball-nut into the X axis is often difficult. It is also > possibly unnecessary. If there is one place where backlash > compensation stands a good chance of working it is the X-axis of a > lathe. it is never much of a problem with a manual lathe, is it? I > don't think I have ever made a lathe cut where the X axis cutting > force changed direction. True, its either cutting on the OD, or boring in the ID. 2 separate operations normally done by measuring the result of the last cut so backlash isn't a problem 99.999% of the time. 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
