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Added a VFD to my CNC mill
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About a year ago I bought am Mitsubishi VFD for $238 on ebay. It
came with a 190 page installation, setup and operation manual. I took a look at it and indeed it was a really nice inverter that would take single or three phase supply and would run the three phase motor on my enco mill. Most important was that it allowed for external manual control with a speed pot, Parameter Unit, (a fancy keypad and LCD display for programming the unit) and for setting various parameters) and last and most importantly it took a +5 analog signal from an external source for PC control. Well. I finally got around to connecting it to my machine. Wow! I am impressed. So far I am just using the parameter unit for changing speeds. It works like a dream and runs the 3 phase motor much better than the Phase-o-matic inverter that I use to use. Most impressive is that you can program the acceleration and deceleration rates of the motor. Before my spindle would take for ever to coast to a stop. I would have to use the brake. Now I have it programmed to stop in 4 seconds. I am going to figure out how to use the analog signal from DeskwinNC to turn on and off my VFD and set the speed from computer via the G code. I think that would really be a nice to automatically turn on the spindle motor and set the speed via the program. So far I can heartily recommend the Mitsubishi FR200E series inverters. BTW I have been told these normally sell for around $800 but got mine New off ebay for a fraction of that. It sure is nice not to have to change pulleys all the time. Last I would like to know how to calculate the maximum safe speed that I can run the spindle at. I would think that the 3500 RPM 50 Hz motor would cause the spindle pulley to explode if run at 400 Hz. Dan |
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Marv Frankel
Dan,
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I'm also running a Mitsubishi VFD but mine is the S500 series. Up until just the other day, when I read a post from one of the list members, I didn't realize it was possible to control speeds through the CNC driver. That goes onto my list of functions when I design my system. Marv Frankel Los Angeles ----- Original Message -----
From: "Dan Mauch" <dmauch@...> To: <CAD_CAM_EDM_DRO@...> Sent: Sunday, October 27, 2002 11:32 AM Subject: [CAD_CAM_EDM_DRO] Added a VFD to my CNC mill aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if you have trouble. sister site to the CCED group, as many of the same members are there, for OT subjects, that are not allowed on the CCED list. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........ bill |
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Country Bubba
Dan,
According to a pdf file that I have (from NEMA I believe), the max safe speed of a 3600 rpm motor will be 7200 rpm (up to and including 5HP) If you would like, I would be more than happy to mail the file to you. I also have another file from a motor manufacturer that includes this information: "Maximum Safe Mechanical Speed Limits (does not imply constant horsepower capability) Motor @ 1800 rpm Frame Direct Belted* 56-184 5400 2250 213-256 4200 2250 284-286 3600 2250 324-326 3600 2250 364-365 2700 2250 404-449 2700 2250 *Belted per NEMA MG1-14.41 (dated 1993)" However, I cannot find reference to this information in the NEMA file listed above:{( Also, nobody that I have talked with can tell me WHY the belted rate is lower than the direct drive rate??? However, I will also be glad to forward the contents of this pdf to you also if desired. Based on what I gleaned from these two files, on my 60Hz motor, I limited the speed on my RF31 to a max of 100 Hz. With the belting arrangement I have (replaced the 17mm bore original pulley with a single 7/8") on the new 3ph motor, I can achieve speeds of 111 to 2220 rpm with no additional belt changes. Now having said this, there isn't much torque at 111 rpm and I have stalled it a time or two at that speed. As a matter of fact, I also had it kick out on overload due to the extremely low rpm of the motor and lack of cooling:{( Still, I think it was the next best investment to my machine shop since adding the mill/drill. And as you say, no more belt changes. Another feature of my VFD is that I was able to set it up to give direct RPM reading on the panel and I never have gotten round-to building that tach I bought from you:}) At 11:32 AM 10/27/02 -0800, you wrote: About a year ago I bought am Mitsubishi VFD for $238 on ebay. ItBubba OLDER THAN DIRT Country Bubba (Actually the inventor of Country and Bubba) axtein@... LaGrange, GA |
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Hi,
I also use the Mitsubitshi inverter, there on sell on e-bay (ex-stock or something), with full warranty. see this link: .html Hugo for --- In CAD_CAM_EDM_DRO@y..., Marv Frankel <dcdziner@p...> wrote: Dan,series. Up until just the other day, when I read a post from one of the listmembers, I didn't realize it was possible to control speeds through the CNCdriver. That goes onto my list of functions when I design my system.took a takelook at it and indeed it was a really nice inverter that would on mysingle or three phase supply and would run the three phase motor parameters)enco mill. Most important was that it allowed for external manual connectingand last and most importantly it took a +5 analog signal from an runs the 3it to my machine. Wow! I am impressed. So far I am just using the use tophase motor much better than the Phase-o-matic inverter that I everuse. DeskwinNC toto coast to a stop. I would have to use the brake. Now I have it code. Iturn on and off my VFD and set the speed from computer via the G spindlethink that would really be a nice to automatically turn on the recommendmotor and set the speed via the program. So far I can heartily fractionthe Mitsubishi FR200E series inverters. BTW I have been told these time.of that. It sure is nice not to have to change pulleys all the that ILast I would like to know how to calculate the maximum safe speed motorcan run the spindle at. I would think that the 3500 RPM 50 Hz reach it ifwould cause the spindle pulley to explode if run at 400 Hz.aol://5863:126/rec.crafts.metalworking or go thru Google.com to you have trouble.to be a sister site to the CCED group, as many of the same members arethere, for OT subjects, that are not allowed on the CCED list.POSTING THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........bill |
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Dan Mauch wrote:
I am going to figure out how to use the analog signal from DeskwinNC toYes, VFD's are really nice! I'll never go back to a static phase converter. I suspect these motors can be pretty safely operated at twice the rated speed. There was some serious discussion about higher speeds on rec.crafts.metalworking, and people with contacts in the woodworking industry indicated that it was fairly common to run 60 Hz motors at 400 and even 800 Hz, and that motor manufacturers had told them that 400 hz (2 and 4 pole) motors were built with the exact same materials in the rotor as the 60 Hz motors. I am pretty skeptical of all that, and would rather see this first before believing it. I suspect a solid (meaning no spokes) pulley is capable of taking at least twice rated speed. Bridgeport J heads are available with dual speed motors or the high-speed option, to go to 4250 RPM. With the cost of good spindle bearings, I really would not want to exceed that. Now, taking that standard head, and running a 60 Hz motor at 400 Hz, you'd be running the spindle at 28333 RPM. While the spindle probably would not explode at that speed, the pulleys would, indeed, be at dangerous speeds for their construction. I can't imagine the belt would handle this at all, though. V-belts tend to flip over when run at excessive speeds, and then shred themselves in minutes. Truly calculating the max safe speed involves computing radial loads from centrifugal force, and then also analyzing the natural vibrational frequencies of the parts, and making sure you don't operate at a speed where the rotational rate and the bending natural frequency coincide. That is the first critical speed, and resonance can develop into fantastic explosive force in just a few revolutions. It requires a pretty detailed mechanical analysis to figure out where these resonances will occur. 28333 RPM = 472 revs/sec, which is not an unreasonable natural frequency for some of these components. But, all that is meaningless, because bearing life of some of the smaller bearings in the head would be reduced to minutes. Even with the best oil, the spindle bearings would be toast (literally) in a few hours, tops. I have heard of people running Bridgeport and similar spindles up to 7500 RPM or so on occasion, but it seems a bad idea. If you have a real need for high spindle speed, why not put in an auxilliary direct-drive spindle? I picked up a Rockwell/Precise spindle that can run up to 45,000 RPM, and it is DESIGNED for that use. I got it for a song on eBay! Jon |
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Country Bubba wrote:
However, I cannot find reference to this information in the NEMA file listed above:{( Also, nobody that I have talked with can tell me WHY the belted rate is lower than the direct drive rate???Two possible reasons. One, is that V-belts will not stay on pulleys above a certain speed. they will flip over and flay themselves in minutes. This is somewhat diameter-dependent, as the smaller pulleys generate more centrifugal force as the belt whips around the smaller radius, for the same linear belt velocity. Second is the belt puts a radial load on the bearings, heating them more. Jon |
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I should have been more specific. I wasn't worried about the motor
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exploding at high RPM but was definitely concerned about the spindle and brake drum assembly coming apart at high speed. You confirmed my suspicions that calculating the forces would be significant task. I noticed that in the default setting for the parameter unit that the factor max speed setting was 120Hz. That led me to believe that was about max that they would set the speed at. I have only run it up to 75 Hz and am, satisfied that would be sufficient. I didn't buy the VFD so I can get higher speeds, I got if for being able to set various speeds without having to keep on changing pulleys and mainly to be able to command the spindle to turn on and run at programmed speeds. I to have an attachment that clamps onto the spindle for an air turbine for high speed engraving/cutrting Thanks Dan -----Original Message-----
From: Jon Elson [mailto:elson@...] Sent: Sunday, October 27, 2002 10:03 PM To: CAD_CAM_EDM_DRO@... Subject: Re: [CAD_CAM_EDM_DRO] Added a VFD to my CNC mill Yes, VFD's are really nice! I'll never go back to a static phase converter. I suspect these motors can be pretty safely operated at twice the rated speed. There was some serious discussion about higher speeds on rec.crafts.metalworking, and people with contacts in the woodworking industry indicated that it was fairly common to run 60 Hz motors at 400 and even 800 Hz, and that motor manufacturers had told them that 400 hz (2 and 4 pole) motors were built with the exact same materials in the rotor as the 60 Hz motors. I am pretty skeptical of all that, and would rather see this first before believing it. I suspect a solid (meaning no spokes) pulley is capable of taking at least twice rated speed. Bridgeport J heads are available with dual speed motors or the high-speed option, to go to 4250 RPM. With the cost of good spindle bearings, I really would not want to exceed that. Now, taking that standard head, and running a 60 Hz motor at 400 Hz, you'd be running the spindle at 28333 RPM. While the spindle probably would not explode at that speed, the pulleys would, indeed, be at dangerous speeds for their construction. I can't imagine the belt would handle this at all, though. V-belts tend to flip over when run at excessive speeds, and then shred themselves in minutes. Truly calculating the max safe speed involves computing radial loads from centrifugal force, and then also analyzing the natural vibrational frequencies of the parts, and making sure you don't operate at a speed where the rotational rate and the bending natural frequency coincide. That is the first critical speed, and resonance can develop into fantastic explosive force in just a few revolutions. It requires a pretty detailed mechanical analysis to figure out where these resonances will occur. 28333 RPM = 472 revs/sec, which is not an unreasonable natural frequency for some of these components. But, all that is meaningless, because bearing life of some of the smaller bearings in the head would be reduced to minutes. Even with the best oil, the spindle bearings would be toast (literally) in a few hours, tops. I have heard of people running Bridgeport and similar spindles up to 7500 RPM or so on occasion, but it seems a bad idea. If you have a real need for high spindle speed, why not put in an auxilliary direct-drive spindle? I picked up a Rockwell/Precise spindle that can run up to 45,000 RPM, and it is DESIGNED for that use. I got it for a song on eBay! Jon |
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--- In CAD_CAM_EDM_DRO@y..., Country Bubba <axtein@d...> wrote:
Dan,I can't be sure, but I expect that the side load on the shaft and bearings in belted duty is the reason for the lower speed limit. I am most familiar with larger motors (5HP and up, to 600-1000 HP). In the larger sizes, there are different motor designs for belted vs. direct drive. Bearings and shaft sizes, among other things, are adjusted to handle the side loading. John Kasunich |
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Country Bubba
John,
Thanks as that makes more sense than anything I have heard! As stated previously, I have limited my upper rpm, but this is mainly due to the heating that occurs on the lower end of the quill. This has been reported by many and seems to be related to the shaft seal more than anything else. (Poor design)?????? Anyhow, I rarely need any speeds above 2000 rpm. At 08:29 PM 10/30/02 +0000, you wrote: --- In CAD_CAM_EDM_DRO@y..., Country Bubba <axtein@d...> wrote:BubbaDan,I can't be sure, but I expect that the side load on the OLDER THAN DIRT Country Bubba (Actually the inventor of Country and Bubba) axtein@... LaGrange, GA |
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