Clint - I have an older Allen Bradley 1336S drive (courtesy of ebay) - the collection of 5hp units I got without operator panels, and then finding a panel, probably ran me about $150. I don't see those drives at that price ($40 each!) on ebay currently. The motor was a 5hp Craigslist find, about $60. I added a new pulley and bushing for another $100. My power service is in a medium-industrial area, and sits pretty stable at 212 VAC, +/- 1v variance leg-leg, with a recorded typical of less than 5% variance. My mazak says it's at 60.2 Hz - so it's right on the money for USA domestic service. We are on a recent (last 3 years) installed site transformer, and one of only two customers on it.
I cut typically aluminum and polymers, and the load meter has always been less than 50% with the exception of accel and decel. Even in a mild steel or stainless cut, 0.070 engagement, was only 40% loaded. I have inserts that will allow 200thou DOC, but I'm not expecting to use that capacity. My limiting factor really isn't power for my applications, it's surface speed; I top out around 3500 RPM now, and while that's more than sufficient for aluminum at 2", it gets kind of slow at 1/4"..... I do not currently employ an external resistor, although I should. EMC controls the external PID loop, while the drive takes care of the inner accel/decel loop - ie. the drive's accel/decel is faster than EMC and rarely takes precedence, but is there in case EMC (or I) command it to do something stupid. The spindle has a full A/B/Z encoder on it for feedback. It is NOT run in a tight servo-loop, just a relaxed "at-speed" loop. It's fine for threading straight, but needs a little tightening for tapers still. (change in surface speed related). I pulley'ed up the motor as large as I can go (given physical space restrictions) - the 3500 is actually more than what the lathe originally did (2880 to 3000) on it's DC motor, so I guess I should be happy. The motor I have on there now has class-H insulation, so it's technically not inverter-grade - thus I'm not going to overclock the VFD - it's running at 60Hz. Many VFDs you can "freq-up" to 100 or even 120Hz, but consensus is that you really "Should" have an inverter-duty motor for that. Aside from lucky finds, I'd look at either surpluscenter.com or automationdirect.com for "retail" units - probably cost as much to ship as they do to buy - a 5hp motor will weigh about 151 lbs - just enough when crated to be over UPS small package, so it goes by truck. However you could still have yourself a decent motor for about $500. I understand the retrofit cost versus the iron cost - I paid $500 for my Tsugami complete, but $1200 to truck it, and have probably sunk only an additional $2k of gear into it. However, exclusive of labor, it has already paid for itself. I have no doubt my "hobby lathe" will continue to be such until the day it is retired - it's unlikely it would ever be a "completed" project - one more bell or whistle to add to it, a software upgrade etc. If you can find a servo drive for that size of motor, I'd recommend it - if you think C-Axis work will be in your future. You "can" use a VFD to work as a servo drive (hack, cough. disclaimer), but the challenge is that most VFD's have a built in accel/decel profile that has a minimum setting of 0.1 seconds, not 0 seconds or disabled. So although EMC could control the servo loop, it will always have that 0.1 sec (*2) delay. Which won't get you consistent or repeatable results in absolute degrees. I originally had a VFD on my turret toolchange motor, and although it would work, it took a lot of effort and multiple gear changes to get it there. Even then, if it went from one tool to a neighboring tool (like #3 to #4) it would often hunt for a few seconds before it was close enough to let the turret lock again. There is now a real servo with gearhead and a real servo drive on there and the difference is night and day. I don't have a C axis going on my unit yet, but I plan on following what Tsugami did in the past - the headstock has provisions for clutching in and out a secondary servo for fine positioning. Since the mech is already there, I just have to find a suitable servo for it. One final caveat - the firmware in my AB spindle drive is set for forward run only - however I haven't used a tool that I need to run backwards. Ted. ----- Original Message ----- From: "Clint Washburn" <[email protected]> To: "Enhanced Machine Controller (EMC)" <[email protected]> Sent: Tuesday, March 08, 2011 7:18 PM Subject: Re: [Emc-users] Single Phase Lathe spindle motor question > Ted, > > What kind of motor did you go with and what model of vfd do you use? Also > I have not yet purchased a drive yet I am weighing my options. I am > thinking of 5-7.5 hp. With the price some of the vfds are going for I > would pay several times over what I paid for the lathe. > > Thanks, > Clint ------------------------------------------------------------------------------ Colocation vs. Managed Hosting A question and answer guide to determining the best fit for your organization - today and in the future. http://p.sf.net/sfu/internap-sfd2d _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
