>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 $$. 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
