Need help setting up a large lathe (air interlock)

Discussion in 'Tools' started by Entropy455, Jul 25, 2018.

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  1. Dec 11, 2018 #81

    ignator

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    I think you missed the point of this thread. The OP has a large industrial lathe (HUGE to be more accurate), which dwarfs all hobby machines. It has a 3 phase 40HP motor. There is no simple solution to power this in a home shop with single phase power.
    I do want to correct your assertion that VFD's are complex. They are commodity machines these days, and very affordable. 40 years ago, they were just coming to the HVAC market for fan speed control. Now VFDs are in home washing machines, and air conditioning systems.
    Simple is plugging a lathe or mill into a wall outlet as purchased from the tool dealer. Wiring a VFD does take the ability to connect "door bell circuits", as making cords and wire interconnect that operate at AC line voltages and currents takes some domain knowledge to do safely. From reading comments about hobby machinists purchasing industrial equipment, there is this fear of buying a 3 phase machine, as they now must add additional wiring and systems that generate 3 phase, and that may push them into an area where they lack the knowledge. The cost of a rotary phase converter (RPC), purchased off the shelf is moderately expensive. There are many posts about making RPC's home-made. There are many posts about connecting a VFD to a 3 phase motor. If you price a VFD vs RPC, the cost difference is nominally 3:1 less expensive (in the 3HP, 4.5Kw size). There are very cheap VFDs of the Hungyang variety that currently are not reliable (that will change, but gives a bad name to VFDs, and hobbyists have found these $110 USD solutions attractive). Most namebrand VFDs are manufactured in Asia, from quality designs.
    Changing a motor to DC and connecting a speed controller is just as "complex" as connecting a VFD. Both give variable speed. If the motor comes from a treadmill, that takes additional skill to make a motor mount as well the skill to hack the electronics.
    When I see machine shop equipment sold locally, the 3 phase machines are less expensive over single phase. We all are cost sensitive in this hobby, and passing on a machine because of a perceived "complex" power system needs to be understood by those in the market for shop equipment. If a hobbyist does not have the skill to connect a VFD or RPC, they should stay away from 3 phase machines. But that is a small count of hobbyist's that grew up fixing and manufacturing repair parts, as they also repaired electrical appliances, and learned how to work with AC power.

    All that said, my Wells-Index vertical milling machine has a 1960s 3 phase motor. NEMA changed the motor dimensions since this machine was made. That and it has a bastard C-face motor. It would be a major effort to convert to single phase. Originally, I powered it with a home built RPC. This worked but I always had to manually start it, and it was noisy in the shop. I found a very affordable VFD, and I would never go back to fixed frequency operation, as I now can control spindle RPM directly from the VFD display. It makes switching between using an edge finder, drills, boring head, quick and I can convert the SFM to spindle RPM, and dial in the speed to not damage my tooling or the part.
     
  2. Dec 11, 2018 #82

    DJP

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    My comments were not about the discussion to power a very large lathe in a non-industrial infrastructure. I was only saying that any additional complexity is a potential new failure point which is why I prefer simple motor/belt/pulley driven machines for my hobby use.

    Your example of washing machines with VFDs also doesn't sit well with me. My wife and I had a Maytag washer that dutifully cleaned clothes for over 40 years. It was purely mechanical. Our daughter is now on her third modern front loading washer with fancy circuit board. When the board fails the machine is scrap and needs to be replaced. I'm not sure what fails but the added convenience drives complexity and the cost to repair is too high. We bought a new commercial duty washer recently (a clone of our old washer) and expect it to last beyond our lifetime.

    Thanks for the historical overview of creating 3 phase power. Your response is a valuable addition to the forum.
     
  3. Dec 11, 2018 #83

    ignator

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    Agree 100%, my Maytag that came with the house (1972 manufacture) failed from the timer motor (that drives the drum switch) plastic gears, that became embrittled, replaced in 2002. I glued them back together only to have it fail completely.
    Front load washers are nothing but a short lived machine. The circuit boards are not of commercial quality, nor is the valued engineered design. Components are not derated (2x thermal overage), and hence overheat. They do what the industry wants, have you replace them every 7 years.

    Industrial VFDs are a different class of machine. But eventually they will fail. Most likely the micro processor or the memory, as the silicon technology is getting so small that the applied DC voltages cause metal migration, and this is where size matters in silicon integrated circuit design. Same issue with all PCs, although lately it's the OS that has caused me to buy new hardware. But that is why I shut my VFD off, when not used, as well lightning strikes are an issue in my mind.

    I'm with you on complexity, in automobiles I was happy with electronic points, as that was the only issue I ever had with engine maintenance. Folks will say you need the electronics for high fuel efficiency, this is not true, I owned a 1987 Chevy Metro, one liter 3 cylinder. It got 54MPG with a carburetor. And because it was 1400 lbs, was very peppy. But it would be a death machine from crash survivability, as it was #1 in that category, the #2 car was a heavy Buick, the difference was the age of the drivers (very young vs very old). The engine is a Suzuki design, as the early imports were rebadged Suzuki Justi models. In fairness, heavy autos need electronics for fuel burn reduction, but mainly for emission compliance. And that we are stuck with.
     
  4. Dec 11, 2018 #84

    TSutrina

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    VFD creates three phases at the specified frequency. They are designed to connect to three phase induction motors. The output from a VFD is not a good sine wave. Pulse width modulation in effect creates and average sine current into the motor winding. The iron winding of the motor clean up the input to produces a reasonable good torque and motor speed. However, there is a significant amount of heat created. This is the reason that an induction motor for VFD are larger. Basically to deal with the problem you need to derate the motor to a lower power and this is done by lowering the voltage or limiting the current or both. I am a mechanical engineer that worked on the packaging of the electronics for aircraft 400Hz AC power and a few motor drives for induction aircraft 3 phase motors. The problem you may have if you can not get a VFD with sufficient power and want to run the machine as a much lower power level is adjusting the drive to match the winding of the motor. Basically the resistance of the winding is fixed, (may have more then one voltage capacity). The VFD has a maximum current it can put out and you do not want to in effect connect it to a winding that is in effect a short circuit to the VFD. It will go into current limit mode or put out to much current and fail. So the voltage needs to be set lower and how to do needs to be discussed with the VFD manufacture.
     
  5. Dec 12, 2018 #85

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    I have never seen this issue with any VFD powering a 60Hz induction motor. Nor have I seen any mention of this in the VFD user manual. The frequency of a VFD is a square wave driven with a carrier frequency that is a programmable parameter of the VFD. Mainly you change this for noise suppression. True it is not a pure sine wave, but since it has a fast edge, the inductance of the motor limits the current. And the average of these pulses follows a sine wave in nature. Typical carrier frequencies of 3-15Khz, but it depends on the design and IGBT transistors used.
    The bigger worry with a VFD is because V=L di/dt, the Voltage spikes can be big enough to punch through the enamel winding insulation. VFDs today control the dt edge rate to prevent this from being an issue. The issue if seen is from very old motors where the insulation is deteriorating or insufficient for the transients.

    VFDs will reduce the voltage as the Hz is reduced per the V/f program which is a user settable curve.

    Do note that the original OP has no desire to use an underpowered design solution for the lathe's 40HP motor. Because VFDs are using fast edge pulses, they soft start a motor without a large surge current of LRA. The OP also understands the rectifier and capacitor filters are overrated when powering the VFD from single phase input power. Eric's last posts indicated using a 100HP VFD that supports single phase input power, and this will power a 40HP motor.
     
  6. Dec 12, 2018 #86

    Entropy455

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    Modern HE cloths washers are complete garbage (I finally purchased one when my old washer failed). The washer tub would only fill about 6" deep with water, where some cloths were literally out of the water. The agitator moved about as fast as someone turning to get up out of their chair. It took 90 minutes to wash cloths, and they came out dirty. I assumed the unit was defective, so I took it back, and purchased anther brand. It did the same thing - a complete garbage waste of time.

    So I found a lightly-used 1980s vintage Maytag in the classifieds for 250 bucks, purchased it, and now I can actually wash cloths again. I gave the HE unit away.

    Commercial washing machines are quite literally the only new machines out there that will properly soak & agitate (aka wash) your cloths. Avoid anything and everything new that says HE.

    Below is my current big cannon. (this is the largest gun Americans may own without a permit). I only fire it on the 4th of July, to celebrate the 4th of July. It weighs about 2000 pounds, and is road towable. It will rattle windows over a one-mile radius, and you can feel the impulse solidly on your chest for a good 1/4 mile (it's lots of fun to shoot - firing blanks only for safety I might add). I need to get my big lathe running, because I want to turn a properly shaped cannon (aka hourglass traditional-looking) from some 20" diameter solid round bar.
    [​IMG]
     
  7. Dec 12, 2018 #87

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    So there is 'madness' behind owning your big lathe. It does look like fun.
     
  8. Dec 12, 2018 #88

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    I ended up with a top load HE washer, I do not understand the water fill algorithm used, it alternates between turning on water, then swishing the agitator. And some unknown sensor data it uses to determine if the cloths are in deep enough. The lid safety switch prevents watching what it is doing. It's only been in use for a year. I stayed away from front loads for the reason of excess complexity. As well the many complaints of 'organic smells' from bio-degrading soap water. I don't see any conformal coating on boards that are operating in a damp environment. The matching dryer, is gas, I opened it up to install the LPG pilot and valve changes. I don't think there is anything of quality left from seeing how minimal every part is. I should say that it is fantastic value engineering, to take every ounce of quality to ensure an operation life just long enough to live through the warrantee period.
    Maytag used to be made here in Iowa, they closed the plant over 15 years ago. The company morphed with Admiral, and now Amana, the only thing I see that is still of their design is the clips (under the top lid) used to access the machine for maintenance. My parents had a Maytag washer and dryer set that lasted 25 years of use, and used for 4 loads a day as it washed for 10 (I'm 2 of 8 off spring).
     
  9. Dec 12, 2018 #89

    DJP

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    The Speed Queen Commercial brand seems to be of the same rugged design as the old Maytags. We bet our future washing needs on Speed Queen although rebuilding the Maytag with a worn internal bearing was an option.
    This post may not make sense in a forum about metal machining but it explains my philosophy of keeping my hobby lathe and mill as simple as originally designed. Rugged is good and my first Southbend lathe was well over 75 years old when I passed it along to another hobbyist and upgraded to a Myford S7.
     
  10. Feb 6, 2019 #90

    Entropy455

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    Update:

    I just picked up some 1600 amp contactors (three off them) - 200 bucks for the set (surplus). This means I'm back to the phase converter project.

    I'm into the electric motors 600 bucks, and 200 into the contactors. Now I need about 400 dollars worth of capacitors. Then figure about another 300 bucks for miscellaneous supplies (terminals, lugs, indicators, paint, etc). I've already got the wire, a cabinet, and steel to make the frame for mounting the motors (all purchased surplus). Thus my 80 horsepower converter will end up costing about 1500 bucks.

    Additional hidden costs - I need to install a second 200 amp panel in my shop. Figure 600 bucks more (for the panel, meter disco/reco fees, the conduit, feeder wires, etc).

    The VFD would've been cool, but I'm saving 4 grand going with a rotary phase converter. The converter's idle-current will cost me about 66 cents per hour. The capacitors I'm purchasing are rated for 60,000 hours.
     
  11. Feb 6, 2019 #91

    ignator

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    Sorry I introduced a diversion.
     
  12. Feb 6, 2019 #92

    Entropy455

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    No apology necessary.

    As a result of your recommendations, I purchased a 1.5 horsepower 3-phase motor & VFD for my little lathe (super excited about it). I'm also going to retrofit my drill press with 3-phase motor & VFD.

    If anything, I should be thanking you for turning me on to VFDs. . .

    The decision to run a rotary phase converter for my big lathe is simply a function of cost. The contactors I stumbled on are several grand each, new. . . .

    I also have plans to build a distributor test stand, using a 3-phase motor with VFD.
     
  13. Feb 8, 2019 #93

    Wizard69

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    Entropy

    Lots of luck with the rotary phase converter build!

    As for some of the comments from various people about VFD's, I suspect many are misinformed about their reliability. We literally have hundreds of them at work on various 3 phase and single phase installations and for the most part the electronic out last the mechanics they are connected to by many years. The early VFD's where somewhat maintenance intensive, my early years included a lot of PTI drive repairs, but the modern highly integrated drive is a marvel of reliability. I just wanted to set the record straight here.
     
  14. Feb 8, 2019 #94

    ignator

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    Have you figured out the air pressure operation of the lathe, as this was your original post question.
     

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