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Lathe - Variable Speed/VFD

 
 

 

 
 
Variable Speed Control of Motor (Jul 3, 2001) Variable Speed Drives: AC, DC (May 4, 2003)
Teco Westinghouse VFD model FM100-201-N1 (Nov 29, 2001) VSD's (May 18, 2003)
Speed Control for 9" (Oct 23, 2002) Reduced speed on single phase motor? (May 23, 2003
VFD drives (Dec 17, 2002) Speed Control on 14" (Jan 1, 2004)
VFD drives (Jan 23, 2003) VFD on a SB 16" is great but... (Apr 23, 2004)
VFD drives (Mar 31, 2003) VFD's (Mar 16, 2005)
 
Variable Speed Control of Motor
I believe one of the recent postings mentioned how pleased the author was with a variable speed control he had installed on the motor of his lathe. That kicked my brain in gear after a day or two and I dug out the variable speed control for routers, that I have had in the tool pile for years, to look it over. It is rated at 15 amps and designed as a variable control for routers. Can't remember what project I bought it for now, but once I needed to slow down a wood working router for a particular job. Question: What would be the pros and cons of plugging this speed control into my SB9C lathe motor? The motor is the original issue one from 1945 apparently with the condenser can on the top front. Am I likely to burn out anything? Will fine tuning the speed of my turning move me one step closer to Complete Happiness in this World? Comments? Opinions? Bubba K (1009)
DON'T DO IT!!!! This question comes up every once-in-a-while, so everybody PAY ATTENTION. Here's the simple answer: If you are using an induction motor (60Hz single-phase, starting capacitor...) you'll smoke the router speed controller and maybe wreck the capacitor or overheat the motor windings. An induction motor runs nearly synchronous to the line frequency rather than varying its speed based upon line voltage. Your speed control is ONLY good for AC/DC brush-type universal motors (like in routers). If you want variable speed your two options are a DC motor + speed control, or a 3-phase motor and a variable frequency drive. I was tempted to get one of the treadmill motor + controller setups from Surplus Sales for about $50.00, but I hate the sound of brush motors, and since the motor is rated to 6000 RPM, you would not get best performance out of it when replacing a 3450 RPM induction motor. I'm holding out for a good used variable frequency drive. When I find one of those, I'll pick up a good used 1 HP 3-phase motor and do the conversion on my 9" model A. Until then, I'm quite happy with 12 speeds of belt-drive. Cheers, and save the speed control for your router! Paul R. (1010)
Your router speed control is only to be used with AC/DC "universal motors. They have brushes and will run on AC or DC current. Your lathe motor is a capacitor start split phase or induction tupy- totally incompatible with the router speed control. One or the other or both will be destroyed if you try it! Marty (1011)
Here is one sweetheart part of having a variable speed control on my 9" SBL . I weld a lot of pipe , axles and shafts on my lathe. I always put the ground on the material itself and farthest from my headstock and have lots of leather for the ways. I've rigged up a tool post holder for my Profax Mig welder. It took a lot of practice but well worth it . I never before could manage very well to turn the chuck or the piece with one hand and weld with the other .I'd go to fast or to slow, get slag inclusions, porosity in my welds and have to grind out and re-weld and cursing all the time. I found the biggest problem with stopping a weld halfway through the weld was heat warp . This was especially noticeable on the SS blow pipes I build for the glass people . They are a very fussy customer and the pipe has to roll dead true when blowing glass. I use my mobile R9 Lincoln for most of my lathe welding . I have the remote heat control with it so I run it over to the lathe and then I can , once everything gets going smoothly, watch the weld going on and control lathe speed with one hand and heat and wire speed with the other. Too much set up for a small job but when you have a lot to do and a clock to beat it sure is the cat's pajamas. (1012)
Paul, firstly, I basically agree with your conclusion, the 3-phase motor with variable frequency drive is the preferred solution. As far as the 6000 RPM DC motor speed is concerned, even if you couldn't get small enough driver pulleys or have room to fit large enough driven pulleys in the first-belt drive to adjust for the greater motor speed you could always have added an additional stage of speed reduction before the original motor position. Anthony (1018)
Anthony, I just got rid of an extra jack-shaft and belt. I don't want to go back there again ;-) But seriously, I was moving to simplify and make more efficient the power transmission system on my 9" SB. I just finished turning a two-step 9" pulley for the counter shaft. That along with an 1150RPM 3/4 HP GE motor gives me the equivalent of a stock setup. My lathe was missing the standard big cast iron counter shaft pulley and had a an extra jack-shaft and step-pulley arrangement. Extra power loss, and inconvenient to change speeds. Plus, the lowest speed was still too high. Again I'll wait for a VF drive and 3 phase (or VF-specific) motor.  Paul R. (1021)
In the newest issue of Home Shop Machinist there is an ad from a company called Surplus Center out of Lincoln NE for a "2 1/2 HP Variable Speed Motor Kit" for $49.95. Per description: "New ARGORD permanent magnet DC motor controlled by solid state motor controller", "Amps-18.5", "RPM 0-6750","Size 7 3/4 x 4 x 4", "Shipping 14#". Possibly someone who knows more about DC motors than I can decipher the specs, but 18.5 amps doesn't sound like 2 1/2 HP. I can scan the ad if anyone interested, but I'm still trying to figure out if this would be the ticket for my lathe (or my future homemade mill or homemade shaper. Frank (1035)
This motor is out of a tread mill and the 2.5 HP is misleading. The motor won't put out the rating of 2.5 HP at other than its full speed. There was a long dialog on this motor on one of the other lists. It would be better to find a 90 volt permanent magnet motor and controller which will put out constant torque which it what you want. This motor would be more like a 1 HP motor. Yasmiin (1036)
Kinda what I thought, but just to play Devils Advocate would this power a 9" SB (my belt can handle about a third of the 3/4 HP I'm giving it). Small and variable speed for $49.95? Actually I have no intention of ordering the setup for the lathe (I'm perfectly happy with the 3/4 HP I have strapped to it) but it sounds like just the thing for my mill in progress (Phoenix Mill, HSM Jan/Feb 01 thru ?) What I guess I don't understand is the drop-off of torque v RPM in a DC motor. I know you said "more like a 1HP motor" but how does this compare to the 3/4 HP AC I have on the lathe. The motor in the lathe is a beast (ask my poor belt), if I can get the same performance from a $50 treadmill motor. Frank (1040)
1 HP = 746 Watts. 2.5 x 746 = 1865 which, when divided by 18.5 (amps), = 100.810810 volts required. Higher voltage will give higher horsepower. This ignores inefficiencies but is at least a starting point for making judgments. Anthony (1042)
So 18.5A is about 2.5HP. I wonder about torque. To make a short story long, I'm looking at building the "Pheonix Mill" HSM Jan/Feb-?. But his Dave Gingery derived belt drive system is about 4ft long, and I'm looking for a way to conserve bench space. A variable speed motor sounds like just the ticket, IF the torque is there. Frank (1044)
Teco Westinghouse VFD model FM100-201-N1
Does any one have any experience with the Teco Westinghouse VFD model FM100-201-N1 and 1hp motor combination that Dealers Electric is offering on their website http://www.dealerselectric.com/ . I am very seriously considering it for my South Bend 10L (heavy). Any input would be appreciated. Rikard (2274)
This looks like a good deal. I would only question the 1 HP. If its replacing a 1/2 HP motor then it should work great. The motor is fan cooled. It doesn't say if the fan speed is independent of the motor speed. If it isn't then you can go down to about 30 hz. If you go below 30 Hz then you need to be sure that the motor has an independent fan as otherwise the motor will over heat. Yasmiin (2275)
From an electrical engineering standpoint - This looks a whole lot better than the DC stuff from treadmills. You may need some basic electrical savvy but this looks like a very competent package for use with machine tools. I would suggest if you are putting it in a home or home shop, wiring it up by itself as a 240V single phase input to a new breaker in your electrical panel, (or cannibalize the dryer circuit and use that) run all the wiring between the motor and the drive in MC cable or greenfield metallic flex, the rest can be romex or whatever fixed wiring( just not plug-in cable). You might possibly experience some radiated noise from the drive -seen as noise on radios, snow on TV screen, etc. which can be reduced by using all metallic conduit or metallic sheathed cable and putting the drive in a metal grounded enclosure. I think I need at least one of these for development projects. (2276)
I recently ordered one for my 9" Model A, as 1 HP should be great for it. For your 10L, I'm not sure, but probably okay. Although the motor is rated for 1800 RPM (@60Hz), your lathe may take a 3600 RPM motor. Not sure if windage heating is an issue with these motors at higher speed-- still looking for specs on it. Also since its a TEFC motor, could be a problem at low RPM end as Yasmiin mentioned. One thing nice about my setup is that I'm currently using a 1150 RPM motor (custom pulleys), so 1800 should give a nice range with good torque. All in all, too good to pass up. I think you'll find the same. I'd say go ahead and order one. You can make custom pulleys as required to get the best speed/torque performance. As in pjwizr's post, plan to do a nice job with wiring, grounding and shielding for minimal RFI, although you shouldn't be watching TV while you machine ;-). I'll report to the group when I get to playing with mine. Paul R. (2277)
I am going to try and get one for the Seneca Falls that I am restoring. Like others have suggested I will change the pulleys between the motor and the counter shaft so that the motor runs at a higher speed for the same spindle speed I get without the variable speed. Then the 30 Hrz to what ever should give a give belt position on the spindle a wide speed range without going to low or two high. A question for those electrical engineers that still remember this stuff what is a realistic top frequency for the control that won't fry the motor or the bearings? Yasmiin(2278)
Generally an inverter duty motor would have a curve showing derating for continuous operation at reduced speeds, or a chart, or the like, to indicate appropriate design loading so the fan-cooling issue should be taken care of by judicious consciousness of that loading limitation. The design duty rating of this motor should protect it in general lathe service. Also there is the issue of a motor thermal device ( "overload" in electrical jargon): this is not specified in the drive or motor literature on the website and this protection is needed on the drive side to the motor to protect motor from thermal overload. There is no problem loading the 1 HP motor lightly at rated speeds per the derating curve, so if the speeds are OK on the lathe, it should be possible to set up the pulleys to turn the spindle as fast as the bearings would permit at top speed, and then gear everything else down from that. The motor doesn't care what the ratio of the load speed is, it's torque and power ratings are only based on it's rotor speed. Just be careful not to put too much cutting load on the tooling when running the machine fast - it may be possible to overload the mechanical parts of the machine if it is designed for limited HP drive. The variable-speed drive is designed to try to keep the motor turning at its speed setting and will control voltage and current to keep the motor there, even if the load varies, so it's possible to overload the machine and the motor or drive won't know or care. Might be best to use a flat drive on this for a safety mechanism. It also will take more information about the motor and drive to set everything up copacetically, but this looks like a good solid set of equipment to start with. (2279)
I am going to try it (the price is right and I was primarily looking for a phase converter anyways). Now I just need to assemble the hundred or so pieces of the lathe that are on my garage floor after having been stripped/sandblasted/and painted. I should be able to report back in a month or so on my experience. Rikard (2333)
Just received my TECO-Westinghouse VFD/Magnatek 1HP motor combo from Dealers Electric Motor. Everything as advertised. Motor: Magnatek TEFC 143CT mount 7/8" shaft with key Rated 6-60 HZ, 1800 RPM @60HZ, 1HP, 3PH Brand new! Inverter Drive: FM100-201-N1 Input: 1Phase or 3Phase, 200~230V, 50/60 Hz, 4.5A Brand new in original box with documentation. Both items packed well enough to survive the UPS journey from coast to coast w/o damage. I'm Jazzed! Currently my motor has a 5/8" shaft, so I'll either have to bore out that pulley to 7/8", or make another one. Caution, my drive configuration is CUSTOM, so your stock setup will be different. With a rated top RPM of 1800 for the Magnatek motor, you guys with a standard 3600 RPM setup will have problems. My setup uses an 1150 RPM motor with custom 2-step pulleys to get me to the standard counter-shaft speeds. The new motor will put that nominal speed in the middle of the new motor's range (180-1800 RPM). Very nice, indeed! More To Follow. Paul R. (2334)
The standard speed for a South Bend drive motor is 1725 RPM, not 3600, according to "How to Run a Lathe", so it seems this motor would match a standard lathe quite well. Chris (2335)
Better still! My lathe came with a 3600 RPM repulsion/induction motor that looked original, so I figured that's what they came with. But then again, my lathe was real funky. It had a non-back-geared headstock and an extra jack-shaft. I still think 3600 RPM might have been standard with such a large pulley on the counter-shaft, though. Doing some rough calculations, I can leave my motor belt set on the lowest speed and get the effective range of up to 1100 RPM spindle speed, down to 30 RPM w/o going into back-gear. With back-gear, I can get some ridiculously slow RPMs. Paul R. (2336)
Speed Control for 9"
My dad is giving me a 9" South Bend Model B that he bought new in 1948 or there about. It is going to make a great addition to my shop set up of 7x12 and mini-mill. I am wondering if anyone has ever put some kind of DC Motor control on one of these and if so, how? ian (6770)
The things usually come with a single phase 110V AC motor. The only way that you can add a speed control is by changing the motor to a DC motor with a speed control. WW Grainger is a good source for this kind of stuff. It could be kinda expensive to convert. Tom (6771)
Ian; I'm using a 2 HP treadmill motor on my SB13. I made a pulley for the motor that provides a 5:1 speed reduction so fairly slow speeds are well into the torque band of the motor, and if opened up all the way will avoid overspeeding the spindle by very much. This is a '29 unit with bronze 2 piece bearings so 1000 RPM is pushing things, 700 RPM is about the highest you really want to run. The motor is mounted to a plate that in turn is secured to a pair of clamps that go on the rear ways, much as a micrometer stop mounts. There is a piece of 3/4 inch shaft between the clamps, the plate has a block mounted to the underside bored .751 through that the shaft goes through. This allows the motor plate to swing for belt tension while keeping the belt in alignment. The holes in the plate are slots rather than just close fitting holes, this allows fine alignment adjustments of the belt and motor. Stan (6772)
Not true. A Variable Frequency Drive (VFD) can be used to give you any speed you want with the OEM motor. Not that you'd want to run it at 3000 rpm. Tom (6774)
A simple but slightly expensive solution would be to install a VFD. This can be used to drive a single phase or a 3 phase motor. All the advantages inherent in 3 phase such as good starting torques, true reversing can be achieved. There are some motor/VFD sets available on eBay. But you should also be able to just get the VFD and use the motor you already have. One advantage of a VFD over a DC motor/controller is that you can easily switch it between different motors so you can drive/control all the other AC motors you have in shop. John (6775)
I got my DC motor and controller off eBay for around 100.00 Clint (6776)
After mounting a 1 hp treadmill motor on my bandsaw, I plan to do the same thing on my lathe. Old treadmills are a dime a dozen. I found this one dumped on the side of the road. Everything you need is right on the treadmill. I did have a jackshaft on the saw that was used for the old motor, so I ran the DC motor through it also. Sure is a nice setup for any machine that you need to control the speed of. John (6805)
VFD drives
I just purchased a Model A. Unfortunately, the existing motor is 3 phase (1/2 HP) and I don't have access to this service. I am debating between replacing the motor with a single phase 1/2 to 3/4 HP instant reversing or installing a VFD. Can someone comment on the pros and cons of these alternatives? Denny (8043)
Denny, After installing VFD/3ph motors on my 9" SBL and my Mill/Drill, I would recommend a VFD if you can swing it. The only reservations I would have are the size of your existing motor and the fact that it is probably not really rated for variable frequency. That being said, a good 1/2 hp 3-phase motor will probably outperform a cheap 1-phase, and for the most part, a 1/2 hp motor will probably be sufficient. I bought a 1hp package for my lathe, and a 2hp package for my Mill/Drill from www.dealerselectric.com and am quite happy. Lots of folks pick up a VFD on eBay for small bucks also. Paul R. (8045)
Denny I changed both my SB lathes over to 3/4 HP 110 volt with no problems what so ever. I am planning to change out a little longer to DC motor, I have them just have not had a chance to do it yet. There is really no reason for a reversing motor when running a chuck. The only time you would use one is if you run collets and threading If you have a 110volt 1/2-3/4 HP Reversing motor, then yes, by all means use it and you will not have any problems. Clint (8047)
It's been a while since I've work with one of these lathes, but I thought that reverse is important. Don't you need to be in reverse when using the back gears? Denny (8049)
Your using a 1HP VFD package? That's not too big for a 9" lathe? Also, it looks like the cost of an instant reversing single phase motor (not including the new switch I'll probably need) is more than a comparable VFD package. Is that right? Denny(8050)
You will need reverse for metric threading or any threading if you don't have a thread dial. Ed (8051)
Denny, I had the original SBL motor on mine for many years. When it bagged out I bought a 1 HP DC Motor and a Penta Variable speed control / reverse. The Penta control was about $400 CDN but I picked up a brand new motor off e-bay for $50 US so all told it cost me around $500 CDN or say $350 US. I do a lot of small threading jobs so it really shines for this. I have since bought the same set-up for my ML7 Myford so you see I think it works just excellent for what I do. I find that if you have it sometime you'll need it. When you are threading a very small piece it really is nice to be able to run extra slow and be able to stop in ample time without giving yourself a heart failure in the process. I also build up shafts on my lathe with the Mig welder fitted on the tool post. The variable speed is a real winner for this job. Anyway just another fellows opinion for you to mull over. (8053)
Yes. Instant reversing single phase motors are expensive. c (8055)
A consideration when obtaining VFDs to operate 3 phase motors from single phase input; a derating factor is usually given for the VFD, sometimes as much as 40% (depending on load). A 1 hp rated VFD, with single phase power input, is a conservative rating to drive a 1/2 horse 3 phase motor. Fred (8060)
The 1 and 2 HP Teco/Westinghouse VFD's I got are full-rated for 1- or 3-phase. Paul R. (8064)
Paul, The VFD I got from Allen Bradley was derated. Stands to reason that 3 phase at 220V constitutes more power delivered than single phase at the same voltage. I wonder if the TECOs are already "derated". Fred (8066)
A review of what this involves might be useful here. From what I've seen, the VFDs rated for full horsepower on either 1 or 3 phase supply are not "derated" per se - they have been designed with single phase parameters and get 3 phase ability for little added cost. The VFDs I'm familiar with all rectify the incoming AC and place it on a DC "bus" that has a storage capacitor or two placed across it. One way of looking at it is that the capacitor "smooths" the incoming pulses from the power line, and in single phase you get 120 of these pulses per second. With three phase, you get 360 pulses per second, so the capacitor can be significantly smaller in value for a 'three phase only' unit and still sustain the bus voltage high enough under load to supply the full motor rating when it's needed. With the smaller cap using single phase input, the bus voltage will droop further under load than with 3 phase input, and may drop below proper operating values for the VFD. What the manufacturers must do for a dual supply unit is to enlarge the filter capacitor and (sometimes) install rectifier diodes with higher peak current ratings. I mention "sometimes" because solid state rectifiers with large ratings are so inexpensive that they don't always do this. They often use two caps, a smaller one directly across the rectifier output and a larger one across the DC bus, with the bus separated from the rectifiers by a surge resistor (a thermistor whose resistance goes down as it heats up under load). That effectively reduces the starting current requirement rating on the rectifiers, as well as being easier on the bus capacitor(s) as well. So, can you do the same thing to a used 3 phase VFD you pick up on the side of the road? Possibly...though automatic protection circuitry may get in your way - it depends on the sophistication of the design. You need to consider two things - the size of the existing capacitor(s) and the current rating on the rectifier diodes. On many of the models I've looked at, the DC bus is brought out to a couple of terminals on the interconnection strip, so it may be possible to put some additional computer grade capacitors in a safety enclosure and just wire them in, especially if there is a surge thermistor in the line. Capacitor values for a 220v 3 phase unit are typically in the 800uF per rated hp range, but single phase will do better with twice that value. My ancient 3ph to 3ph 220v Emerson uses 1200uF for the 2hp model and 2100uF for the 3hp model, along with a 420uF primary cap across the rectifiers. This is why a 3hp unit is often desirable for, say, a 2hp motor if it was designed as only a 3 phase input VFD...it already has a higher capacitor value built into it. Bus voltage for a 220v unit is normally 300-340vdc, so you'll need 400vdc or 450vdc capacitors. If you need a surge thermistor, places like Digikey carry those at very reasonable prices. Model number will depend on load rating of your VFD. All this assumes that you have already run into problems with using the unit at full rated power. I have a 1HP 460v 3 phase in VFD I have been running on my Hardinge HLV-H with single phase input for almost 2 years now and never had the 1HP motor noticeably slow down, even on the heaviest cuts I've demanded of it. Same with the Bridgeport, using the old Emerson. If you have the luxury of buying what you want, then either a single phase rated unit or ~50% extra capacity in a 3 phase input unit is the easiest way to go. But if you happen on a good deal in a smaller VFD, you might want to simply try it before you start adding capacitors and all that it entails. Mike (8080)
Mike, You mentioned that you use a 460V VFD on your Hardinge using single phase input. Are you using a Buck/Boost transformer set-up? I have been curious about whether one could use a VFD that was rated for 370 or 460 volt and adapt it to the lower voltage of 230. without using set-up and then set-down transformers. Probably not but it couldn't hurt to ask. I have been wanting to put a VFD on my mill but finances are tight. Also, could one power a 3 phase input VFD from a rotary phase converter? Or would the VFD balk at the third leg not being properly balanced? Webb (8082)
Webb. The first transformer in the chain is a small 480/240 lighting transformer I picked up at a hamfest for $20, though I do see them on the bay occasionally. It's used in reverse, which gives me between 470v and 500v on the output with my line - a bit high for my liking, considering the replacement cost of this 'high end' GE VFD (a $135 eBay purchase - the smaller 440-480v VFD's on eBay seem to go for very reasonable amounts.) At any rate, because the GE specs stated a 506v max input spec, I put a 24v control transformer secondary in series to buck the voltage down by 24vac. Overkill perhaps, but the VFD seems quite happy with that. Wish it were that easy. In theory you should be able to change the operating design center of the output side to use the lower bus voltage, but there are so many different designs out there, many of them using embedded or single purpose chip sets, that a redesign would be a significant task. I wouldn't even attempt it unless I had a detailed maintenance manual on the unit. The older 1970s and 80s VFD's like my Emerson are probably more amenable to that kind of conversion since they tend to use discrete components and you can diddle with values and pulse timing, but I wouldn't recommend trying it unless you had some experience in the area. Like 'they' say, it all depends. It's not clear to me why one would *want* to, if a simple 240/460v single phase transformer would do the job. The only reasons I can foresee why you would want to are: 1) if the particular VFD protection functions were inflexible and you couldn't work around them somehow while using a single phase input (happens with some sophisticated VFD's), or 2) if the VFD protection functions were inflexible and weren't capable of tolerating the 'wild' leg voltage excursions one occasionally sees from an otherwise tuned rotary converter that is forced to serve a number of machines with widely varying horsepower, or 3) if you had other machines you wanted to run simultaneously off of the rotary converter. Now, all of those are valid reasons and may fit your case, but it's generally simpler for a home shop to settle on one or two VFD's (220v and 440v) and switch them between machines, given their low cost. My 220v unit powers the Bridgeport, vertical bandsaw, and Baldor grinder (not all at once), while the 440v is dedicated to the Hardinge. Remote start/stop buttons are paralleled for the 220v version, but I *do* have to remember to throw the primary switch on for whichever machine I'm using. Mike (8090)
Mike, The reason I asked about using a Rotary-Phase converter in combination with a 3 phase input VFD is so I could get the full rated output of the VFD that would otherwise be de-rated by about 40 to 50% when connected to single phase. I thought of a couple of other questions (while I have your attention). My mill has a drum switch. Would I bypass this when using a VFD (relying on the start/stop and forward/reverse built into the VFD unit)? Or just throw the drum switch on (forward say) and then activate the VFD? What about if your equipment uses a push button station and contactor motor starters? Webb (8098)
Lots of variables in there, Webb. The VFD isn't a highly inductive load like the drive motor slaved to an idler motor, so it's not clear to me that all the phase relationships will support each other as is the case with a straight rotary system with two motors. The conventional wisdom would have us believe that would happen, but I haven't tried it so I can't say for sure. If you already had a 3 phase converter, there's absolutely no reason you couldn't hook it up and give it a go. On the other hand, I would try the VFD on single phase by itself first, as I mentioned in my first note. If that wasn't satisfactory, then you can move on to the other options like a larger capacitor or an idler motor. It all depends on what you have on hand to start with. I realize that may sound unsatisfactory to someone who has to order everything from scratch, but the incredible variety of VFDs out there force us into this step by step mode, or risk disappointment in the end. *IF* the VFD is sufficiently oversized (and I'm talking about perhaps a 5hp unit for a 1hp load, then you can generally keep the old method of powering up. It all depends on the sophistication of the VFD, as many of them will protectively shut down when faced with a sudden increase in load like that. It also depends on the value of that capacitance I mentioned, as it has to sustain the bus voltage high enough to avoid shutdown from that mode as well. Having said that, using a VFD in this mode isn't really getting the maximum out of the unit. It will baby your motors in a number of different ways if you use the VFD to start and stop them, which means leaving the drum switch on all the time and then using a small independent pushbutton station to control the VFD. For example, the GE/Fujitsu unit on my Hardinge went through a "motor measurement" cycle when I first turned it on, measuring all of the motor parameters to a high degree of precision, and uses that to constantly monitor the health of the motor while it's running - including temperature. It also has adjustable starting and stopping ramps to ease the motor up to speed and down to a stop. I think that's typical of all the later units. I just use the Hardinge control circuitry to set up the contactors in "on" condition and then use the VFD for the rest. It also solved another nagging concern for me - over the years I've had and seen more than one heavy workpiece get loose from the chuck or faceplate. Since I stand to the right of the plane of possible ejecta to operate the carriage, etc., that forces me to reach across that plane to hit the off control. Sometimes scary, not to mention the coolant stripes I used to get on my shirt. I mounted a new pushbutton station for the VFD under the right coolant tray lip - pointing up at a 45 degree angle - and now I don't have to look like Don Knotts, reaching in front of a vibrating workpiece. Lot more convenient, as well. Mike (8104)
Webb, I'm pretty much in agreement with Mike. Bottom line, modern full-rated inverter drives (VFD's) for small motors (2HP or less) can be had for single-phase 220 (home shop) readily. It just makes no sense to string together static or rotary phase converters ahead of the drive, unless you have old-technology stuff laying around that you want to attempt to use. Also, static phase converters cause you to derate your motor output anyway. As far as using the drum switch is concerned, NOTHING should go between the VFD and the motor (for 2HP or less motors and cabling under a meter in length). I rewired my drum switch to provide the control signals to the VFD so I would retain the same "user interface." One draw-back with VFD's is that they are dedicated to a particular machine. With a rotary phase converter, you can set one up in the corner of the shop and run several machines (typically, one at a time) while a VFD should not be shared or moved from machine to machine (needs to be reprogrammed). Yes, smooth start/stop are very cool to have, and may keep you from spinning your chuck off. Also make sure you don't configure an E-Stop brake that will stop the spindle dead in its tracks. That will surely launch your work-piece across the room. No more dimming house lights with the programmed acceleration/deceleration from your VFD. When first shopping for big iron, I was hesitant about considering machines with 3-phase motors. No more! With the price of VFD's so low, and competitive with phase converters, I'll never dismiss a machine because of its motor. When the motor on my mill/drill started failing, that was all I needed to install a new VFD/inverter-duty-motor combination. I'm hooked. I like the smooth start/stop and variable speed so much I'm considering VFD/motor retrofits for my big Rockwell wood lathe and my delta table saw should I ever need to replace those motors (dream on...). Paul R. (8110)
One of the enormous values of this group is that you get different perspectives to fill in a more complete picture of the issues involved in any particular subject. This is especially true of the more complex technical questions that seem to abound in our interest area. Paul's comments are 'right on', and are essential elements for consideration in making decisions in the VFD arena. I couldn't agree more, Paul. The eternal economic conundrum is the number of permutations that I left out of the equation. A person with an existing rotary will have a different perspective than one having a 460/230 transformer sitting in his garage, and so forth. That may change the ideal goal of having one VFD per machine, which is obviously Nirvana. This is certainly the ideal. Pragmatically, one may wish to leave the drum switches in place and relegate certain functions to the VFD and others to the drum switch. For example, it may be more trouble or cost to add a switch for the VFD to perform the reversing function, than to leave the drum switch for that function and add a separate on/off station for simple VFD power on/off. The variations to consider can get complex fairly quickly and of course depend on the particular VFD remote options available and what remote switches you have available in the junk box. Absolutely! Ummm, well, I take that back...maybe not true for all of them. The earlier VFD's don't use a computer to program functions tailored to a specific motor, so they are more easily used with more than one motor connected to them. The 1985 model Emerson Accu-spede (sic) that I use for several machines is one example of a VFD that is so lacking in sophistication that it doesn't care *what* you have connected to it as long as it is within its power rating. :-) Of course, it was only $75, so I can't complain too much. It has a single programmed ramp up/ramp down rate that is not instantly adjustable to connected motor needs, but that's no worse than developing a compromise tuning setup for a rotary converter used with several machines. Really excellent points for a threaded chuck, or one which has a large rotational inertia! I have yet to understand why instant reversing motors are considered a good idea, even for a threading function on a mill. I've come around to that view myself. Of course, it also has a large dependence on one's hobby budget. Thanks for inserting those missing pieces, Paul - really helps fill out the picture. Mike (8121)
VFD Drives
I understand that many members of this group use VFD's to power their lathes by converting single-phase power to three-phase power. Is this 230V single-phase to 230V three-phase? Or is it possible to use 110-120V single-phase converted to 110-120V three-phase? I have a 9" S.B. model A with a 110V, single-phase, 1.0 HP Emerson motor (which uses nearly all 15 available amps when running, BTW, and when someone turns on a light to one of the bathrooms, poof goes the circuit breaker, followed by screams from me and the fellow in the bathroom). Second question: To use a VFD, I assume I'll have to replace this motor with a three-phase motor. Is is possible to acquire 110-120V three-phase motors? Bilal (8866)
VFD's are normally meant for 230v 3-phase 60 Hz to 230v 3-phase 0-120 Hz (or thereabouts). Most can do 230v 1-phase to 230v 3phase with some reduction in maximum power (usually can operate at 2/3 of rated power) this is a function of the size of the caps in the VFD. I have never seen 3-phase power at 120v, I have only seen it at 230v or 460v. c (8867)
A VFD will convert 220 single phase to 220 3 phase. I am not aware of a 110 volt option, but it might be available, just not sure. If your 1 phase motor is 110/220 you might be able to wire it for 220 (if you have 220 available) and you will draw less current (amps). I am keeping my eye out for a 1 HP motor to power my 10L, I'd be willing to trade straight up my 1/2 HP motor for your 1 HP motor and that would reduce your current load to the affected circuit. I don't live but 15 miles from you (Gaithersburg). Contact me offline if interested. My mill is powered by a VFD so you are welcome to come by and see that also. Mark (8871)
There are two variants of "low" voltage 3 phase. 120/208 star(Y) and 230 open delta. 120/208 can be thought of in terms of the letter Y. The central point of the Y is grounded. The voltage from the ground to any end of the Y is 120 Volts. The voltage between any two ends of the Y is 208. 110 V single phase loads are connected between the ground point and any of the 120 V ends. The best description I have for 230 open delta is to think of it in the shape of the letter L. The voltage on each leg of the letter is 230 V. It is also 230 V between the ends of the two legs. One of the legs is grounded in the center giving 115 V between the ground and the two ends of that leg. This leg of the circuit is exactly the same as the typical 120/240 V single phase supply. All single phase loads 115 V loads can be connected to that leg. Any 230 V single phase loads can be connected across either of the legs or between the ends of the two legs. As far as I know the small 3 phase motors are always connected to the ends of the legs regardless of whether you have 208 supply or 230 supply. Likewise they are rated to run on both voltage ranges. So although there is no 120 V 3 phase motor you can run a 208 V 3 phase motor off 3 120 V phases. You would have to check the suppliers but I think some converters will work with a 110-120 Volt single phase supply. They might not be able to deliver the full 110 volts on each phase though so it would be de-rated. Using a 220-240 V supply will require less current and electrically it is easier to supply the rull rated voltage. Sorry about the mix and match of voltages but 110, 115 and 120 are really the same thing. Same thing for 230 and 240. 208 is different and only comes from the Y connection. Hope this helps. If not hit delete. John (8876)
Anybody stuck with a 3ph motor should just make a converter- really easy stuff, just get your caps from McMaster and a surplus 3ph motor. Tom (8880)
I'm replying from British Columbia Canada. You are requesting info on Variable Frequency Drives, but the context of your question indicates that you are talking about Phase converters. I would first take a look at the size of the breaker that in on the line. If it is only a 15 amp breaker, it is not large enough to handle your one HP motor. Check this out with your local electrician. I suggest that the motor you are using is adequate for your 9" SB and does not merit the hassle of 3 phase conversion. I had two lathes in my shop until I sold them. They each had 1 HP single phase motors on them which were completely satisfactory. Now having said that I also have a 16" Colchester lathe which is my pride and joy. It has a 7 1/2 HP three phase motor driving it. Being in a domestic situation, the shop behind the house, I have had to go to a Phase converter. I am using a ten HP three phase older type motor which I picked up for $50.00 complete with a start up motor mounted atop of it. With this in place I am now able to power all the machines in my shop, lathe, mill, press, punch, and air compressor. It has worked well for close to 20 years now with complete satisfaction. If you would like to have a look at this situation, and have access to the "Home Shop Machinist" magazine out of Michigan, I have a writeup in May/June 1997 complete with pictures of my shop. Desmond (8881)
VFD drives
I've installed three VFD controllers made by KB electronics, sold by B B motor controls of Long Island NY. 1/2hp units sell for 150 dollars, a 1hp sells for 200. They are bare chassis, and must be installed in a protective enclosure. I use a plain electrical pull box, without knockouts, and drill my own conduit holes as needed. I just put a 1/2hp unit on my 9" model A, and couldn't be happier. Also changed over to a vee belt pulley set, driving a 46" type 5L cogged belt. I set minimum motor speed to about 60 RPM, acceleration and deceleration at about 1-1/2 seconds so that chucks won't unscrew. Actually at low speed, reversing is almost instantaneous. This makes power tapping and die threading simple. On my mill, I set the accel and decel for almost nil, as the inertial loads on the spindle are insignificant. Dave (10029)
Better deal here I think. Hey If you are looking for a VFD try this link these guys are great and you get a nice unit that needs nothing but wired in and your ready to go. I got mine last week and it works great! http://www.dealerselectric.com Frank (10033)
Maybe, but I prefer to mount a knob actuated speed potentiometer near my on off switch. I wouldn't care to fumble with touch pad switching when speed needs to change urgently. Dave (10036)
Dave it is very easy to put a remote complete with speed control pot, and fwd rev switch , and on off switch. The whole thing fits just great in a single box mounted on the original switch pad on my SB 13x40 I can email you pic's if wanted. Dee (10037)
I see your point! However that is a feature you wouldn't have on a milling machine (without adding it yourself) If you had 3 phase power and didn't need to convert it! Would you ? I put a E STOP button between my VDF and the panel for just that reason. I didn't want to have to try and hit that small key pad button in a real emergency! (10038)
The Teco unit allow remote controls and the manual explains how! (10040)
Right to all. There is no absolute answer, and everyone is going to stand behind their own product! I made a new control box that is similar to a Cutler Hammer drum switch housing- bent up of two pieces of 14 gage steel. On the model A, it mounts on the left hand gear guard, just like south bend standard! On the front of the box, I mounted a three position maintained switch- 22 mm industrial type with two NO contact blocks in back. That controls stop-forward-reverse. On top of the box I mounted the speed potentiometer. The power on-off is only operated once a day, so I mounted it out of the way on the side of the junction box enclosure. That hangs off the back of the rear drive motor mount casting. Both my mill and lathe are set up the same way, and with the same electronics, both the switches flip and operate the same way. Dave (10042)
Variable Speed Drives: AC, DC
Two questions about variable speed: How many of you have a variable speed drive of some type and do you find it very useful? For those of you with some experience with variable-speed motors, what kind of system would you recommend: AC PWM (pulse-width modulated), DC PWM DC SCR ....and for the DC, shunt-wound or permanent-magnet? (10795)
I had one of the "tread-mill" motors on a 9" lathe and it worked, but not that well at low speeds. I also have a VFD on my mill drill and love it, but again at real low speeds, it just doesn't have the torque. Between the two, I like the VFD best. (10799)
I had to convert a Swedish miller from 460VAC 50Hz 3ph., and used a PMDC motor with a "BAV" (Big-Assed Variac) speed control. Has worked very well for several years, and am glad I converted. For the story see http://www/gearloose.com  I am seriously toying with the idea of doing the same with my Model A, because the product I make appears to machine best _between_ two of the fixed belt speeds. Besides, there's a guy on here who needs my AC Motor! (10800)
I have a 1HP VFD/motor setup on my 9" model A and LOVE IT! Most of the time I leave the flat belt on slowest speed and use the VFD to set the desired speed. Granted, the only way you can get real low-speed torque is to use the back-gears, so don't expect to do heavy threading or large diameter heavy cuts w/o back-gear. Personally, I would not use a DC brush motor on my lathe. They are too whiny and the slow-speed performance lacks. I also installed a 2HP VFD/motor setup on my mill drill. You can check out some of the pictures in the mill_drill Yahoo group's Photos section, http://photos.groups.yahoo.com/group/mill_drill/lst under "PaulH's VFD Installation". Paul R. (10809)
I will be getting one for my mill here in another month or two, to run a 2HP 3phase which is one of there big advantages. 3phase motors are like $10 per HP used and there is nothing to them compared to single phase capacitor motors with all the junk inside them. Plus 3 phase pull less amps per HP and a $250 drive will power a 3HP 3Phase no sweat. Kerry (10818)
VSD's
Some people add "chokes" (copper wire wrapped around a steel donut) to handle voltage transients with VFD's. ah, the good old days... I remember them well. the Graham 6 step drives, the Parametrics and Reliance PWD drives.... for some time the pwm drives have been using IGBT's. the high frequency offers signals that are actually better than the 3 phase sine wave from the wall. A simple PWM drive will power the motor for a normal application, a Vector drive will start a motor at higher torque AND can be used for synchronous motor speeds, very good speed regulation. A DC drive can deliver 150% of starting torque. A lot of people de-rate drives and use a 3hp for 2hp motor. but that is usually because they have the wrong drive. Often the drives are selected for cost rather than performance as from what I have gathered, E-Bay is one of the suppliers. you get what is available. And then there are those who figure that running a drive at 3/4 of it's rating will just increase it's life. All the drive manufacturers have sales and engineering sheets that will help in the selection of a drive. some time spent reading will pay off in the long run. http://www.reliance.com/prodserv/standriv/appnotes/d7725.pdf  Dave (11194)
Dave and Kerry, I looked at your link and I guess you missed this part... C. The speed regulator section provides gate pulses to the continually alternating Insulated Gate Bipolar Transistors (IGBTs). The relative on-to-off times for pulses to be successively fired is continually alternating so as to create a sinusoidal voltage pattern at the IGBT output. The wave frequency is altered to produce variable speed outputs. As I read this description, "gate pulses" and "sinusoidal" still means that there is a stair step ramp up and down (albeit very fine steps). I didn't mean to imply that VFD's aren't good. On the contrary, I believe they are the way to go. I just meant to point out that the signal output from a VFD is different from the signal provided by your power company in regards to 3 phase. As to your friend that builds rota-phases for a living; has he put an oscilloscope on his rota-phase and an ampere meters on all leads? I doubt it. If he did, he would find it doesn't produce true 120 degree 3 phase output. The simplest test I can think of is to take a volt meter and measure the three phase-to-neutral voltages. Most rota-phases will put out relatively good phase-to-phase voltage but their phase-to-neutral voltage of the generated third leg will be off. If he puts an autotransformer in his rota-phase, then you can get full HP but it has to be tuned to a particular load. No good for a shop that has varying loads (i.e. different pieces of equipment being turned on and off). Webb (11197)
Reduced speed on single phase motor?
Is it something that should be tried. I have a 3600 1HP motor that I would like to have at 1700 RPM now because it's a polisher and has dual shaft I don't want to gear it down. and go through pulley's and all that. if it is something that can't be done or would not be cost effective I'll just gat a 1HP 3 ph and another AC drive. Which is what I plan on doing to my 9" junior except I think I'll go with 1/2 or 3/4 in 3PH because of the added torque from the better motors. Can ya tell I like the AC drive. I don't know what I would do with out it. Maybe hand crank the Mill? Or do the make a AC drive for single phase motors? Kerry (11350)
Single phase motors don't lend themselves to variable speed operation due to the fact that they have a set of windings in them that only operate during starting. These windings are switched out by a centrifugal switch. As long as the motor stays at or near its operating speed the start windings are out of the picture. If you try to slow it down you will cause the start windings to be activated. These coils draw excessive current in order to get the motor up to speed. If they are kept connected for an extended period of time the motor will overheat. 3 phase motors are superior in many ways to single phase motors, if you can use em do so. Rob (11353)
Kerry, Would you like to sell that 1HP, 3600 rpm polishing motor? I think I can get you just about any kind of lathe motor you need. Let me know what your motor needs are and if possible, please send me a couple of pics of that 3600 motor you have. Maybe you would be interested in a trade? I live in Rhode Island so shipping may be calculated. (11360)
Kerry, The only way I know of getting an induction motor to run at a slower speed is to use a VFD. The RPM. of an induction motor depends on the number of "poles" inside the motor (windings) and of course the cycle rate of your power. Here in the U.S., all power is at 60 cycles per second (at least what you get out of your service panel - I'm not talking about long distance transmission). Therefore, the RPM of a motor (no load) is 7200/(# of poles). A 2 pole motor is 3600; a 4 pole motor is 1800; etc. But if you change the cycle rate coming into the motor, you change the RPM of the motor (remember that we're talking about induction motors). That is what a VFD will do. Now with all that "blather" aside, I'm curious why you want a slower buffer? Buffing, like most forms of metal working, is about SFM (surface feet per minute). I'll admit I don't know a lot about buffing but what I do know from the gunsmithing field is a 1 HP 3600 RPM buffer turning a 6 or 8 inch buffing wheel would work just fine. Webb (11381)
Yep you're right you can run a 6" wheel on a 3600 rpm motor but an eight inch wheel to me is pushing it and I don't like the speed. I set up our shop at work with a 3/4 HP 1700 RPM Baldor buffer and a full set of 8" wheels from brownells after I brought my setup in and sold them on the idea. but after using the bigger wheels at a slower speed I feel I get more control and it takes longer to burn up a part. Kerry slower speed is to use a VFD. The RPM. of an induction motor depends on the number of "poles" inside the motor (windings) and of course the cycle rate of your power. Here in the U.S., all power is at 60 cycles per second (at least what you get out of your service panel - I'm not talking about long distance transmission). Therefore, the RPM of a motor (no load) is 7200/(# of poles). A 2 pole motor is 3600; a 4 pole motor is 1800; etc. But if you change the cycle rate coming into the motor, you change the RPM of the motor (remember that we're talking about induction motors). That is what a VFD will do. slower buffer? Buffing, like most forms of metal working, is about SFM (surface feet per minute). I'll admit I don't know a lot about buffing but what I do know from the gunsmithing field is a 1 HP 3600 RPM buffer turning a 6 or 8 inch buffing wheel would work just fine. (11409)
Speed Control on 14"
Anyone familiar with the variable speed control on a 70's vintage 14"? This is the one with the increase and decrease buttons and an analog meter for readout. From seeing it disassembled, it looked like the speed was varied by a pair of variable diameter pulleys. I'm hoping this is the case so that I can use a static phase converter to power the lathe. If it is actually a VFD, I don't think I can put a static phase converter in front of it. Wally (16126)
Even if it is a VFD the static converter should be ok. Sounds like its what is known as a reeves drive, If it has the double cone pulleys. Those things are rugged and smooth operating. Just make sure the spindles are clean and well lubricated, but not over lubricated. RC (16177)
VFD on a SB 16" is great but...
I just finished installing a Variable frequency drive on a older 16" SB lathe. It uses 230VAC single phase power in and puts out variable frequency / voltage from 3 - 60HZ and 12 - 203V 3 phase. I installed an older 3 HP, 3 phase motor so I would still have great power even down at lower motor speeds. It's fabulous! I set the min speed to 3 Hz and it just crawls making it easy to center using a dial indicator. I am having trouble with the 2" woven flat belt slipping a lot, though. I've used belt dressing which has helped, but I still have the slipping problem with even moderate cuts. If I replace the belt, what is the best material to use that just won't slip? Has anyone found a great solution to belt slipping on the larger lathes? (18592)
Leather belts need a minimum diameter pulley based upon the thickness of the belt. All flat belts should be run on a crowned sheave. Too much belt dressing is counterproductive. You may have multiple minor issued adding up. Urethane flat belts grip fairly well and are tough. JP (18594)
I use a nitrile rubber coated polyester belt on my 16/24 with a 5hp baldor motor. The grip is very strong and sticky. Works great . If the bearing throws oil on it I just wash it off with ivory soap and clean the cones. It never needs dressing. (18904)
It sounds good, but what about the clip? I'm concerned about it making noise when it runs. Ed P (18911)
Yeah, it ticks as it hits the cones, but not very loud at all. it doesn't slap like you'd think. after a little while I didn't notice the ticking anymore, but I also didn't hear my old, useless, soggy-ass leather belt sliming all over the cones in a heavy cut as the rpms drooped, especially on the highest speed with the small end of the cone! (my machine runs a 5hp Baldor motor, with a 5-1/2" motor pulley so I get about 1200rpm in high "gear" ) c.m. (18927)
VFD's
Thanks, Jim B, Gabe, Bernard R and all VFD informed members for the VFD info. I just finished packing the guns and rigging equipment for my trip to Maryland. My cloths are still in the dryer, but the trailer is hitched to the truck with all lights working and the tires aired up. From what you guys have said about these VFD s ; they look like they are affordable, work well when set up correctly, vary the speed well without loosing much, if any, power when run nearest to 60 Hz (for heavy work). And I can keep the old motor, while ditching the rotary phase converter. If you can set it up like Bernard said with a simple pot controlling output frequency it would be great, as the ones on the ships required pushing small buttons in the correct sequence to change the output. I have the old drum switch on the pipe mount coming off of the lathe bed, a very stout unit. Would it be possible to mount a box with the forward/reverse switch being a 3 position toggle switch, the pot for speed control, a digital readout for spindle speed, motor speed or output frequency, and maybe a big red non-returning emergency stop button to be located remotely from the box that houses the VFD, say on the old stout pipe mount? When I get back I am getting one of these VFD s. I did not know the prices were affordable. BTW, if you want to get a rear T. A. screw (cross feed screw) out of a 13 SB lathe with a taper attachment, do not put the end of this screw 4 away from the wall behind the lathe. Put it at least 8 away from the wall with 10 being better. I am going to have to move my lathe when I get back as I want to overhaul the apron / saddle / cross feed next. I have a small 25 by 35 shop that has no extra room in it (the machine tool hobby must share space with a Jaguar hobby, motorcycle hobby, welding hobby and my ammunition), 4 was not worth all the rigging that I am going to have to do to move the lathe 6 away from the wall (zoning does not permit moving the wall). I like this users group. You guys are knowledge rich and other than a certain powerful lawyer, gentlemen. I wish you all well in my absence, as we do not have a computer in Maryland. Maybe one of my shooting friends, a computer sciences professor, at the University of Maryland can get me on line up there, after all, he talked me through getting this computer working to do what I want it to do. Nick (26113)
Nick, When it comes to buying the switches, you need light duty. preferably gold plated, instrument types. The signal to the VFD are likely 24Volt at about 10milliAmp, (the VFD provides the voltage source all you need is the wire and the switches) at these levels normal house hold switches do not provide reliable switching. My own preference is illuminated push button switches, one for motor ON/OFF and another for motor reverse, www.mouser.com has a wide selection. All the VFD's I've used have a digital readout which can be set to show different parameters, I normally leave mine showing output frequency. A chart showing VFD frequency with corresponding RPM at your normal gearing and back gearing is easier than doing the conversion in your head. The way I would wire it up would be, incoming ac line to the main switch, then to the emergency shut down, mounted on on near the machine and then to the VFD. In use, the existing Fwd/Stop/Reverse switch is permanently left Fwd, then put tape or lock it in some way to prevent operation, only use your push button switches to operate. (VFDs don't like having their motors disconnected when running.) Bernard R (26124)
Nick, VFDs just recently became affordable. About 5 years ago, a VFD rated for 1HP was close to $1000. Now, you can get the "basic" type for around $200, new. There is now a "vector flux" type that has good torque throughout the range, but they aren't cheap. To run a 250W motor with a VFD I was given the following price for VFDs rated at 1/3 HP. "basic VFD" 115V input/230 3 ph output constant torque 15 to 60 Hz no provision for tachometer based feedback or add-ons $160-$200 "Vector flux" 230 V 1 ph input/ 230 V 3ph output constant torque from 0 to 60 Hz ability to use tach feedback and other neat add-ons $500 (just the controller) $300 for Tach feedback module I went with a speed pot on my mill setup. After you setup your SB to run with a VFD, you won't want to run it any other way. A VFD/3 ph setup is my preferred way to make something that isn't variable speed, variable speed. It beats DC and old mechanical pulleys hands down, which is why they spec AC drives on today's CNC machines. Gabe (26133)
Gabe, Try www.automationdirect.com , a Hitachi sensorless vector drive for 1/2 HP is listed at $269, I'm using the 2HP unit for my mill @ $399 (less when I got mine). Bernard R (26137)
Nick, I purchased a 3HP Hitachi VFD from Drives Warehouse on eBay. I have been absolutely pleased with it thus far. I love this VFD. Jim (26147)
They certainly have excellent prices. I'll go there when I eventually make my lathe variable speed. I did my mill because 440 RPMs was not a desirable slow speed, coupled with the fact it took a metric frame motor, made VFD/3-phase the only way to go. Unless my VFD breaks or something, it won't ever have a single phase motor on it again. My lathes have acceptable low range speeds and single phase motors, so it is hard to justify doing them immediately, though converting them to is high on my wish list. -Gabe (26148)
Nick I think you have made the correct decision for your situation, I installed a VFD for a friend's wood lathe a couple of years ago when prices were higher. there are a couple of wrinkles to optimizing the package. In my case I even had the single phase motor rewound to 220V,3ph. because of a European flange mounting and long shaft. Expect rated torque from minimum speed to about 1800RPM and constant HP (decreasing torque) from about 1800 up to 2700 speeds above that are impractical even though they may be theoretically possible the usual motor would probably shake itself into oblivion. Jim (26182)
 
     
 

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