On Thursday 18 August 2016 18:07:00 Martin Dobbins wrote: > >For threading, either with the g76 for internal/external threads, > >internals limited by the back off clearance your tool gives you > > without hitting the threads on the back side of the hole. And you > > want all the grunt you can get, so the 1810oz probably is the best > > idea. > > .......... > > >But for more normal turning, you'd soon feel the need for more rpms > > than that motor can muster...... > > Hi Gene, > > I had a fruitless search for the torque curve for 1810oz/in stepper > following Andy's suggestion. So last night I went delving though > history to see if I could find original information on this stepper > driven spindle idea. > > This was some testing, which we shall (politely) call "empirical > results", much abriged outcomes: > > Equipment: > NEMA 34 1841 oz (yep that's right, was 1841oz/in, now 1810 oz/in is > more cost effective and performs better) MA860H stepper driver > 69 VAC unregulated power supply > 1:1 with spindle > > stainless steel (grade not mentioned) 1 inch diameter. It was noted > that turning this with a standard Sherline motor required 0.001" per > pass with copious lubrication in an attempt to prevent work hardening > > One inch long passes were made with a DOC of 0.005"starting at 800 > RPM, the test was terminated at 2000 RPM without a stall. It was > stopped at 2000 RPM not because that was the limit, but because the > user thought that was more than they would ever need. > > 0.5" dia free machining steel threading tests > 20tpi @ 0.005" per pass starting at 250 RPM, the stepper motor was not > sweating at 1000RPM, but stalled at 1500RPM. Best finish obtained at > 250RPM (!) > > At 1000RPM the the Z axis was moving at 50 IPM, that is just not > possible with the standard Sherline 20 turns per inch leadscrew, the > lathe used in the test had been modified with a Haydon Kerk 4 tpi > leadscrew on Z > > The big stepper looks to be good for 2000RPM and maybe more, and has > plenty of torque at low speed. > > A Clearpath servo suitable for this application plus power supply and > cables would probably cost more than the lathe. Although I like the > "made in the USA" idea, the stepper solution is lot less $$.
Agreed. And I have a saying when it appears that it will work, gopherit. I need to see if I can rewire this 1600 for parallel, which ought to speed it up considerably. But its 22mh per winding, so I don't expect miracles. And then tell us how it works when you've lived with it for 2 weeks. A question though, that 1800+ motor is going to be heavy, heavy enough perhaps to pull the Sherline out of alignment? Pix of it wnen mounted would be nice. :) I am likely going to have fun making a mount for that 1600 I have as I just bought a 2505 ball screw & nut, C7 grade, 1450mm long, with bearing kits etc. I'll have to make everything else it touches of course. And it will be about a month arriving from China. In the meantime I can be working on a new apron, hiding the x moter on the back of it. And a compound replacement similar to Andy's Holbrook casting. I think I found a place for the Z motor when I took the quick change box off. It looks like I can put a plate of 1/2" alu, spaced out on some 1/2" thick spacers that might let me put the thrust end bearing block on the inside back of it, and the motor on the front in a good stout nema 34 bracket. With a 1/1 belt drive, probably. We'll see, because the closer I can get the screw to the bed, the less swarf it will have to self wipe off. > > Martin > > > > > > > > ________________________________ > From: Gene Heskett <[email protected]> > Sent: Wednesday, August 17, 2016 10:37 PM > To: [email protected] > Subject: Re: [Emc-users] Clearpath Servo For Lathe Spindle? > > On Wednesday 17 August 2016 22:39:46 Martin Dobbins wrote: > > That depends on 2 things, Martin. > > 1. And likely the most important by far, is the coil inductance. > > > > A motor with only 2 millihenry's of inductance can achieve full coil > > currents quick enough to have usable torque at 500 rpms. The same > > motor frame, wound for the same starting torque but has a 15 or more > > millihenry inductance will use less operating current to run at 5 > > rpm than the 2mh one, and will use perhaps 1/3rd the current. But > > it will be all tapped out and may not ever get to 500 rpms under > > zero load. > > > > 2. The supply voltage fed to the driver, raising it will get the > > current flowing quicker, but trying to make that 15mh motor turn as > > a usable high speed motor, could take more voltage to overcome the > > inductance than the driver can tolerate. > > > > That has a nasty tendency to break the mirror and let all the smoke > > out. > > > > I replaced a 1600oz/in motor used as the Z drive on a G0704, with a > > 950oz/in. Where the high inductance of the 1600 fell over was at > > about 27 ipm. The newer, smaller motor with a new self-contained > > psu/driver, can now run that close to 40 lb head up and down the > > post at 70+ ipm and doesn't break a sweat even when rigid tapping. > > > > Look at the Clearpath torque curves, they fall over at a rate > > virtually the same as a good stepper. The 'real' substitute will > > generally be a decent BLDC 1kw servo motor. That is what the much > > higher priced MC series is, with a 3 phase drive built in. > > > > > > Gene, > > > > Thank you for educating me. > > > > I couldn't find the torque curves for the Clearpath drives, your > > google-fu must be better than mine <grin> > > Not goggle-fu, although mine isn't that good, but if you go clear to > the bottom of the motor selector page, theres a link that say, skip, > look at all of them. Click it and you get the whole catalog. Scroll > down the list till you see an interesting one, and click on its part > number, which will take you to a page with all that info. Look > articularly at the torque vs rpms graphs, and you will see there is a > huge difference between peak, and steady state pull. That flat line > going to the left to zero speed, is the maximum steady torque over a > longer period of time without overheating something. > > > What TPI does the lead screw Z axis on your G0704 have? > > Its a 2005 stytle, meaning a 20mm pitch diameter, and 5 turns equals > an inch of travel. > > > I thought the 1810oz/in stepper was probably overkill in the spindle > > application, and I did wonder if a more modest size stepper would > > work. The people that have done this claim to have tried all sorts > > of sizes before arriving at that. The only requirement is to thread > > mild steel at 0.005" pass and a spindle speed of 150 to 500 rpm > > (depending on size) and to completely replace the Sherline motor for > > turning operations. > > For threading, either with the g76 for internal/external threads, > internals limited by the back off clearance your tool gives you > without hitting the threads on the back side of the hole. And you > want all the grunt you can get, so the 1810oz probably is the best > idea. For G33 and G33.1 use, again grunt is king. Either of those > routines are married to an encoder on the spindle for z axis movement > synch. And the tap absolutely cannot be allowed to slip else the synch > is lost and the threads already cut will be damaged. Thats a huge > problem when the tap is a 10x1.5 but its shank is only 7mm. And er20 > collets with a square drive socket built in are in the $30 and up > each, per size range. Which explains why that spot in my toolbox is > still empty. :( > > But for more normal turning, you'd soon feel the need for more rpms > than that motor can muster when cutting a 10 thou by 10 thou chip. > > > Do you have a link to the 950oz/in you used? > > Something I got from ebay. That sale is long over, but you can likely > find another just like it. Something that has 8 wires, not 4, so you > can wire in series for buckets of grunt w/o pushing the driver, or in > parallel, with the driver set for 2x the current, same grunt but can > turn faster. > > > Cheers, > > > > > > Martin > > > > > > > > > > > > > > > > ________________________________ > > > > -------------------------------------------------------------------- > >-- -------- _______________________________________________ > > Emc-users mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > > Emc-users Info Page - > SourceForge<https://lists.sourceforge.net/lists/listinfo/emc-users> > lists.sourceforge.net > This list is for users of the Enhanced Machine Controller (EMC). > Topics include how to obtain, install, configure, and use EMC, as well > as other general EMC related ... > > > > > > 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 > ---------------------------------------------------------------------- >-------- _______________________________________________ > 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
