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AC vs DC

Discussion in 'Woodturning Discussion Forum' started by Larry Mitchell, Feb 14, 2021.

  1. Larry Mitchell

    Larry Mitchell

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    Like many, looking for a new mid-size lathe. Rather than discussing brands/models I would like to hear comparisons between power supplies, 220v 1hp Servo and 110v 1.75hp AC in particular. Lathe size being 14” to16” throw and 24” between centers.
     
  2. Ed Jarvis

    Ed Jarvis

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    I agree with you larry. I live in an apartment cant get 220 V. I am looking for a 14" swing lathe. quality constructed and cant afford to go to the top end of the lathe market to get one.
     
  3. Dean Center

    Dean Center

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    You'll find a lot more choices in new lathes at 16". The Jet 1640 is 110v at this time and a very nice lathe. (Older ones had an option for a 2 hp motor and presumably would be 220v) Used lathes of 14" include some Reeves drive lathes that would be problematic.
     
  4. Bill Blasic

    Bill Blasic

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    Nova has a new 14" Midi type. I have one but you may like it.
    Nova Comet 14DR Midi Lathe a VS 1 HP lathe
     
    Timothy White likes this.
  5. Larry Mitchell

    Larry Mitchell

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    Thanks to Dean and Bill for their input...appreciate you both.

    Below are the specs of my first choice, 220v Servo motor being the reason for original question.

    2E8E1F60-9535-42D1-B81A-5DE1A1E16422.jpeg
     
  6. Doug Freeman

    Doug Freeman

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    I think Harvey lathes are the only thing available with a dc servo motor. The servo motors are supposed to have better low speed torque vs same hp ac vfd. You need to search the web to find actual speed and torque values for different sized motor drives using different technology. Add another technology to your search - switched reluctance motors, offered in the Nova DVR lathe series, as well as their drill presses. Based on the research I’ve done, the info is not readily available. Mainly you find descriptions of the tech and why the design is better vs others, but not much direct value torque vs speed, ie its 25% more at 200 rpm or whatever. You will also find people’s opinions on particular lathes/drives, and “it’s a lot better than my previous acme lathe”, which usually was a smaller cheaper lathe. Not that many people with direct experience using many lathes with different drive technology. I suspect that’s why you arent getting a lot of comments.

    A couple of other lathes to look at would be the Nova Saturn 16 x 24, and Grizzly G0838 16x24 and G0844 14x20. Laguna has a 15” swing as well.
     
  7. Larry Mitchell

    Larry Mitchell

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    Thanks Doug, kinda figured that was the reason, was looking for an info short-cut. Yes, my choices are the Harvey T40 (14x24) or the soon to be released Record Power (16x24) Coronet Envoy. Only limitations are 220v access or paying more for features I won’t use/need/want because its 115v. Good thing I’m in no hurry. LOL D339B137-9F6C-40A7-A422-4A1AA9454290.jpeg
     
  8. Doug Freeman

    Doug Freeman

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    What are the main features you want/need and why? Sometimes people think they need a certain feature but are unaware of alternative methods to achieve the same result with the turning, and many more options are opened up.
     
  9. Larry Mitchell

    Larry Mitchell

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    $2000 budget (because I don’t need/want a big butt status quo lathe), Bench mount (have 25”x72” #150 maple top table or a 500# hydraulic 36” x 48” cart that will allow my wet sharpener to be along side lathe), 14-16” swing, swivel headstock (back issue), 24” between centers (tool handles or rolling pins will be longest I’ll turn), auto eject tail stock, ability to turn oak (have 10 acres of it.)

    AND...something different. You say Honda, I say Subaru...you say Kawasaki, I say KTM.

    Don’t want/need a sliding headstock to turn outside, legs/stand to store away.

    Getting hands on is difficult...no dealers close, 200+ miles to nearest.
     
  10. Doug Freeman

    Doug Freeman

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    I think my pick would be a Nova Saturn. Has legs that are relatively small and easy to stash away, 16” x 24”. ~1.75 HP on 120v. I’m probably a bit partial - I have the full size Galaxi. No issue turning 15” oak bowls. Excellent outrigger. I can stall it with a 5/8” gouge but I have to try to do so. Core oak bowls without a problem. It might not be “different” enough for you. I have KTM and Suzuki, Im not brand loyal. If interested you can get hands on with my Galaxi. I’m 150 mi north of you. I visit Melborne a few times a year - I love riding Hwy 9 from there west to Hwy 5.
     
  11. Larry Mitchell

    Larry Mitchell

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    South 9 aka Devil’s Backbone (3 miles South of me) is the reason I retired to AR from AZ.

    Thanks for the offer and suggestion Doug.

    429385C4-A101-4A17-B310-162192387A07.jpeg
     
  12. Doug Freeman

    Doug Freeman

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    Well, we have the same taste in bikes. Is that a 990 Duke? This pic was taken at the 215/103 intersection near Oark. I try to get down to AR 5-6 times a year. If interested I'll take you on a tour of the best bike roads southern MO has to offer.

    KTM.jpg
     
  13. Larry Mitchell

    Larry Mitchell

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    Love me some of that peanut butter pie from Oark Cafe!! Sold the bike a couple years ago, things happen and after 56 years of riding various styles it was time to move on. Bike is 990 Super Duke R, one of only 500 imported in 2008. Rode a few areas in Missouri with my Goldwing. This is during a desert race in SoCal on my 1982 KTM 495....couple months before Barstow to Vegas. A8D689AF-E0BB-4346-8C77-B5CAC7F9CE5D.jpeg
     
  14. Doug Freeman

    Doug Freeman

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    Do any trail/dual sport riding in AR? I do some on a DR650. AR dirt roads and trails can turn into something else without much warning
     
  15. Roger Chandler

    Roger Chandler

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    My understanding is that an A/C motor/inverter combo will have more torque at low end speeds than a D/C Servo motor with controller. My former G0698 with 2 hp D/C motor would hunt at low speeds, and does not have the torque that my A/C motors with inverter has. The inverter can be programmed to maximize torque ratios and sync it with rpm’s. This info was explained to me by an electrical engineer, and has been proven out in my experience with the lathes I have used and owned, which includeds Powermatics, Jets, Robust American Beauty, Delta, Serious SL 2542, and of course Grizzly. The servo motors are good, but for coring and big wood, I would much rather have the A/C motor with inverter.
     
  16. Doug Freeman

    Doug Freeman

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    Thanks Roger. The info I find says the opposite, dc servo has more torque at slow speeds. The info I find on the G0698 says its an AC inverter drive not DC. Your direct hands on experience with many different lathes certainly helps. The fact that the top line lathes all use AC inverter drive says quite a bit about the subject. I would like to find info on a direct comparison (same HP/amp) of the Nova switched reluctance vs AC inverter at low speeds, below 500 rpm spindle speed. I suspect they are similar due to the gearing used with the ac inverter drive allowing higher motor rpm. The Nova motor can hunt a bit at slower speeds as the load increases. Over ~300 rpm things clear up and it isn't noticeable.
     
  17. stu senator

    stu senator

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    Pure DC motors have high torque at low speed. At any voltage the starting torque is determined by the voltage applied, the armature resistance and a motor constant determined by it's design. As the motor accelerates a back emf (electromotive force) develops that is again determined by the motor design and speed.This back emf plus the armature resistance then limit the current. At operating torque the input current is limited to the resistance plus the back emf plus some windage loss. If the torque increases (deeper cut) the current goes up and the speed is reduced. Hence hunting. The controller must compensate.

    Basically this means that at stall and low speed a DC motor draws a lot of current and is limited by the power supply and thermal mass of the motor (overheating).

    This is for a basic DC motor but holds mostly true in the newer type drives.

    The DC motors and power supplies as well as the AC lathes have to limit something and hence there are tradeoffs in any lathe and motor design.

    Make your choice on what you think you need and want. Not the details of the drive. A lathe is a tool and chose what you need based on cost and performance of the whole lathe not the parts.

    Stu
     
    Last edited: Feb 16, 2021
  18. robo hippy

    robo hippy

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    Doug, isn't that supposed to be Missery???? Grew up in St. Joe. Have one brother who lives on Table Rock Lake. I do miss real thunder storms, and lightening bugs though.... Daughter did basic training in Fort 'Lost in the Woods', and stayed up all night watching her first real thunderstorm...

    I always figured out motorcycles were too dangerous, so I took up hang gliding....

    robo hippy
     
  19. Larry Mitchell

    Larry Mitchell

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    Location (City & State):
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  20. Roger Chandler

    Roger Chandler

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    Doug, the 18/47 G0698 I owned for 5 years & then sold it to our club had a 2 hp D/C motor with controller. The newer 18/47 Grizzly G0733 that replaced that model, has a 2 hp A/C motor/ inverter. I have currently in my shop a G0766 22/42 with 3 hp A/C motor with Delta “M Series” inverter, and a G0800 24/48 with 3 hp A/C motor with the “EL Series” inverter. My Delta midi 46-460 has a D/C motor with controller.

    At low speeds, the torque from the A/C motor is noticably more than any D/C motor lathe I’ve ever turned on. Not sure about where your info comes from, but back when I was trying to research the A/C vs. D/C issue, I got input from several experienced lathe owners, 2 of which were “sparky’s”. Or Electrical Engineers, who steered me towards the A/C direction since I wanted my lathe to handle coring and big wood.

    At any rate, I sure wish you great success in your search and choice of lathes, as each individual turners unique situation needs to be factored into their choice. My Former G0698 18/47 is still going strong at our club, after 13 years, without any problems,. Most turners don’t turn much below 200 rpm’s so a D/C servo motor will likely serve them just fine. I do a good bit of big heavy/unbalanced wood and needed the high torque at low rpm’s, to keep the lathe from walking with unbalanced blanks. Best of luck!
     
  21. Larry Mitchell

    Larry Mitchell

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    Okay, final decision made...Record Power Coronet Envoy. Many thanks for all the information, suggestions, offers and motorcycle memories.
     
  22. Mark Jundanian

    Mark Jundanian

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    Congratulations. Now you will have to write a review for the rest of us.
     

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