# VFD and Motor for Lathe



## saltytri (Sep 28, 2009)

I'm about to pull the trigger on a VFD and motor for a HF 8x12 lathe that will be converted to CNC. This VFD seems to be about right:

http://www.wolfautomation.com/Product.aspx?ProductID=19500

I'll use a 56 frame TEFC inverter duty motor. So here are my questions (are you out there, Barry?):

The lathe is supplied with what is supposed to be a 3/4 HP motor. Not that I believe that rating, of course. I've read everything I can find on VFD conversions and the conventional wisdom seems to be that it is a good idea to move up a little in power, especially to get enough torque at low RPMs. In this instance, the VFD is a sensorless vector type, which should help with the torque. And, the HF three-step pulleys can be retained, which will allow a reduction factor of about .46. So, should I get a 1 HP VFD and motor or spring for 1.5 HP at an additional cost of about a hundred bucks?

This VFD comes standard in a NEMA 1 enclosure and is available in NEMA 4 for another hundred bucks or so. Not having seen the NEMA 1 unit, I don't know if it would be OK in a lathe environment. I do plan to put it right on the lathe. It may well be possible to house it in a protective box but, if this is necessary for a NEMA 1 model, I may be bucks and time ahead with the NEMA 4 version.

Lastly, does anyone have a specific recommendation for the motor?

All suggestions will be much appreciated.

David


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## 65535 (Sep 29, 2009)

Baldor or Leeson motor, Nema4 enclosure if mounted ON the lathe or near it.


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## wquiles (Sep 29, 2009)

65535 said:


> Baldor or Leeson motor, Nema4 enclosure if mounted ON the lathe or near it.



+1 on all points

Barry just finished his VFD here (mine will happen soon as well) - we are both using NEMA4 VFD units:
https://www.candlepowerforums.com/threads/241878


As a point of reference, I converted my 8x to variable speed (but using a DC motor and controller) and I highly recommend the variable speed capability:
https://www.candlepowerforums.com/threads/193712

Will


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## saltytri (Sep 29, 2009)

There are a bunch of superficially similar VFDs out there. Seeing the Lenze unit on Barry's drill press is what tipped me in that direction!

How about the HP issue. I'm inclined to think that 1 HP will be plenty for the small, and mostly aluminum, workpieces that this lathe will handle. Especially with the sensorless vector drive and a quality motor. I'd appreciate some other opinions on this before I jump.


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## precisionworks (Sep 29, 2009)

David,

The two drives are close in price ... $209.00 for 1.0 hp and $261.25 for 1.5 hp. Either one will do a good job for you, although the 1.5 hp has some advantages.

On a vector drive, the motor produces full torque at all frequencies from 60 Hz down to 1 Hz. BUT, a 1.5 hp motor has twice the torque of a .75 hp motor, which is a real advantage.

All electric motors produce full hp at full rpm. If you plan to run the motor at half rpm, you need to double motor size.



> This VFD comes standard in a NEMA 1 enclosure and is available in NEMA 4


A NEMA 1 enclosure is "open" for ventilation purposes. It keeps fingers and tools out of the enclosure, but allows metal chips, dust, cutting oil, coffee & beer to get inside. You can mount the drive far away from the lathe & remote control the drive with the software already built in. Or you can put the drive inside a metal box that has 4X the volume of the VFD ... which ends up being twice as large as the NEMA 4x enclosure.

NEMA 4x (IP65) means the drive is totally protected from dust & protected against low pressure water jets from any direction ... also known as a washdown enclosure. The cost is higher, but you never have to worry about a stray chip killing the drive.



> does anyone have a specific recommendation for the motor?


I like Baldor, and eBay usually has lots of 3-phase Baldors for sale. If the standard motor is 3450 rpm, you'll want to use a motor with close to the same speed. If 1725 rpm is standard, you'll want to replace with that rpm.

For the low rpm motor, look at M3546:

http://www.baldor.com/products/deta...08-230/460&winding=34WGX269&rating=40CMB-CONT

For the high rpm motor, try M3550:

http://www.baldor.com/products/deta...600&hp=1.5&winding=34WG0283&rating=40CMB-CONT


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## precisionworks (Sep 29, 2009)

> There are a bunch of superficially similar VFDs out there.


I have three SMVector drives, and find them easy to install & configure. Another popular drive is the Teco-Westinghouse JNEV series. Lower in price but only available in NEMA 1, used by quite a few people on the Practical Machinist forum.

1 hp $131
http://dealerselectric.com/item.asp?PID=417

2 hp $177
http://dealerselectric.com/item.asp?PID=394

Both are 230 volt single phase input.


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## saltytri (Sep 29, 2009)

Thanks, Barry. That tells me what I need to know!


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## saltytri (Oct 1, 2009)

precisionworks said:


> I like Baldor, and eBay usually has lots of 3-phase Baldors for sale. If the standard motor is 3450 rpm, you'll want to use a motor with close to the same speed. If 1725 rpm is standard, you'll want to replace with that rpm.
> 
> For the low rpm motor, look at M3546:
> 
> http://www.baldor.com/products/detail.asp?1=1&page=1&catalogonly=1&catalog=M3546&product=AC+Motors&family=General+Purpose|vw_ACMotors_GeneralPurpose&phase=3&hp=1&rpm=1400-1800&enclosure=TEFC&voltage=208-230%2F460&winding=34WGX269&rating=40CMB-CONT



I'm completely with you on the NEMA 4 VFD.

I've been reading up on motors and it looks like inverter duty motors are spec'd with insulation class F or H. The Baldor M3546 is a general purpose type that is spec'd with insulation class B. Is it really necessary to have a inverter-specific motor with F or H insulation or is this lower level of Baldor good enough?


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## saltytri (Oct 2, 2009)

No need to answer that last question. The 1.5 HP version in a 145T frame is the M3554T. This does have F class insulation. I found a closeout for $176 and ordered it. SCORE!


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## precisionworks (Oct 2, 2009)

> Is it really necessary to have a inverter-specific motor with F or H insulation



There are four motor insulation classes - A, B, F, & H. [FONT=Arial,Helvetica,Geneva,Swiss,SunSans-Regular]The temperature capability of each insulation class is defined as being the maximum temperature at which the insulation can be operated to yield an average life of 20,000 hours.[/FONT]
 
A: 105° C - 221° F
B: 130° C - 266° F
F: 155° C - 311° F
H: 180° C - 356° F

The letter tells the max operating temp of the motor, which allows you to use an IR thermometer or contact probe to check motor shell temp. Which is why you cannot use a bare hand resting on the motor shell - even 221° F is too hot to touch for long.



> inverter duty motors are spec'd with insulation class F or H


They are, as they are most often a TENV (totally enclosed _non ventilated_) design. Since the TENV motor has no external cooling fan like a TEFC (totally enclosed _fan cooled_) all internal motor heat is removed through conduction/convection from the heavy shell. These motors will run 24/7/365 at 1 Hz (1/60 of nameplate speed) and be very happy.

It's interesting that all the major motor manufacturers build all of their motors with Class F or better insulation. When a motor like the M3546 is rated for Class B use, it means that the motor is designed to operate within Class B temperature limits. Since the M3546 is a fan cooled motor, and the fan is driven by the motor shaft, you'll want to add an auxiliary fan if you plan to run the motor for long periods at low speeds under heavy loads. Most home shops don't need the aux fan as they never get into low speed + full load + long duration operation. Check your motor shell temp and add a small electric fan if the shell ever reaches 266° F.



> Is it really necessary to have a inverter-specific motor


Rarely in the home shop or small commercial shop, as the general purpose motor will run within the accepted temp limits. If the motor is in a factory that runs 24/7, and the motor is heavily loaded and run at low speeds - then you need the inverter duty motor. They are overkill for most typical users. But the design is bulletproof, and a few show up on eBay for next to nothing, so get a TENV if one is available. If not, the M3546 will work just as well.


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## saltytri (Oct 2, 2009)

Thanks for that very clear explanation, Barry. That information makes me feel just fine about the motor I just bought. It wasn't a screamin' eBay deal but pretty good nevertheless for a quality item.


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