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Quoting - Message: 7Date: Sat, 13 Jun 2015 14:42:37 -0400 From: Gene Heskett <[email protected]> Subject: Re: [Emc-users] was Suitable transformers = hens teeth To: [email protected] Message-ID: <[email protected]> Content-Type: Text/Plain; charset="iso-8859-1" On Saturday 13 June 2015 12:05:11 Greg Bentzinger wrote: > Gene; > > We really need to break your DC motor fixation. If you think PCW's > 5i25 is neat just wait until you start using a VFD controlled spindle. > > Odds are that a better replacement motor and VFD will cost near the > same of what your planning to build to support that marginal OEM DC > motor. That marginal motor is easily replaceable with something with serious grunt that is right at home at 5 grand at the armature, perhaps 1100 at the spindle. The power supply in each case is the majority of the cost, but with Jon's PWM servo driver, slightly modified, I've found I CAN manhandle a treadmill motor fast enough to do rigid tapping, with grunt enough to drive the tap. None of those vfd things, designed to turn at 24k rpms for engraving, can even begin to drive a 4-40 tap, let alone a 1/2-13. And for those situations where I don't have the grunt to do it in one pass, I have already written pack tapping stuff to wrap up the G33.1 with. > > I have several great treadmill motors and some motor controllers for > them, motor controllers intended for a treadmill motor are incapable of doing the control needed. Jon's pwm servo amp, with increased wire gauge in the toroids, can turn that treadmill motor around from 3 g's at the artmature, 300 at the spindle, in a time frame quiter comparable to the vfd if allowances for the flying weight to be reversed are taken into consideration. On my lathe, that flying weight is well above 10lbs as its swinging a 5" 4 jaw chuck. But that is not using the treadmill controller, which cannot actively stop the motor. Jons PWM Servo amp can. > but trying to keep fine tune of RPM vrs load is a hemroid and > using those controls for reversing just isn't practical. Then there > was the heating issue of running the motor at lower RPMs. I no longer try to subdue those BBLB controllers, they decorate a shelf now. Jons PWM Servo amp is a breath of fresh air in comparison. > I would get a 1.5 or 2hp motor with a lower 60Hz rpm spec then over > speed it as needed so you have plenty of low rpm power. And just how do I spin a 2.2kw water cooled, 24k revs motor at 250 rpm's and have enough torque to throw a .015"x.015"x3/8" chip 2 feet away? -- ^ ^ ^ ^ ^ ^ No idea where you came up with this - never said anything about water cooling or trying to use a 24K router type spindle. I actually said a LOWER rpm rated motor (@60Hz)- such as a 1725 or below. I dropped "56C 1.5hp 3ph" into ebay search and the first thing that popped up was ebay item#4601799582 Buy it now price of $139 - I'm sure a better deal can be found, but this was the first item that popped up New 56C/TEFC 1725rpm 1.5hp 5/8" output shaft inverter rated, 10:1 Variable torque, 2:1 Constant torque Direct drive 1:1 this motor would provide: 172.5 rpm @ 6Hz 1725 rpm @ 60Hz - Nominal motor spec - Optimal 3450 rpm @ 120Hz 5170 rpm @ 180Hz 5750 rpm @ 200Hz I would not trust the Grizzly spindle bearings @ 6000 rpm unless I had removed, checked fit, regreased and set the bearing preload. Now if you got ambitious and wanted to do a step-pulley drive: Underdrive the spindle 1:0.5 86.25 rpm @ 6Hz 862.5 rpm @ 60Hz - Nominal 1725 rpm @ 120Hz 2587 rpm @ 180Hz 2875 rpm @ 200Hz Overdrive the spindle 2:1 345 rpm @ 6Hz 3450 rpm @ 60Hz - Nominal 6900 rpm @ 120Hz > On a side note you would still have the Pico drive available for your > old mill so little things like engraving could still be done on it. > Its actually on my lathe. Thats a PMDX-106 on the mill, driving a 1.8 amp rated, 2500 revs at the spindle on the mill. The OEM pass hexfet died years ago, and was replaced by one from a dead computer psu. Nearly zero heating now, it could do a 400 watt motor just fine if I ever get around to using the motor I took out of the lathe. > That 240V is just waiting to be used... I found a toroid to fix that last night. Admittedly, the PMDC motor has brushes to wear out, where the vfd doesn't. But where do I find the power to spin a 1/4" upcut solid carbide tool with that vfd driven pipsqueak? Can that vfd and a water cooled motor do 47hz output and turn a 1/4-32 tap 180 revs in steel? I'm sure you would have no problems tapping @ about 300 rpm. Why piddle around with a 1/4" endmill when a 3/8" is a better buy - save the 1/4" for finishing the corners. I had no idea what could really be done with the tooling I all ready had until I went to the WESTEC tool show and watched other machines plow through metal like butter. I was still thinking small. Good question that. Cheers, Gene Heskett End quote & reply - Greg BTW the motor picked would put you close to the same as what Anders Wallin used for his build. http://www.youtube.com/watch?v=uhaKQH2CCGI ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
