motor size

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mikechoochoo
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motor size

Post by mikechoochoo »

I have a big old 19 inch Le Blonde lathe that is missing its motor. It has a factory Cullen Three horsepower drive on it, missing the motor but would a three hp single phase motor be big enough for this beast. The three hp is cast into the side of the drive and is a 3.
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Richard_W
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Re: motor size

Post by Richard_W »

I ran a Le Blond that had a 10 hp high torque motor in it that only ran at 800 rpm. My model 16 Pratt & Whitney has a 7 1/2 hp motor. I would think that 3 hp would be under powered. This isn't one of those Le Blond slide bed lathes that came off an airplane is it? As I recall they had small motors to save weight. I have only seen one of them.

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Harold_V
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Re: motor size

Post by Harold_V »

A great deal depends on the speeds at your disposal and how you intend to use the machine, although I tend to agree with Richard. Older lathes, those made before tungsten carbide was in use, often are geared exceedingly slow---and do not require huge motors. If you expect to use your machine lightly, no carbide, and not taking serious roughing cuts, you may get by with a three horse motor, but my Sag 12 Graziano (a 12" machine) has three horse. It's adequate for the machine and is capable of taking some serious cuts with negative rake carbide. I would not be satisfied if it had any less power. Don't know if this helps, or not, but that's how I see it.

H
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LIALLEGHENY
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Re: motor size

Post by LIALLEGHENY »

I have a 19" Leblond Regal and it has a 5 hp motor from the factory. I also scrapped a 19 Leblond that had a 7.5 hp motor on it. Eventually I am going to swap the 5 hp over to the 7.5 hp. Why? I run mostly insert tooling and at the higher rpm range which insert tooling prefers, I have many times slowed the machine down to the stalling point because 5 hp isn't enough. Like Harold says it all depends on what tooling you are going to use and what material you are turning.

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Bill Shields
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Re: motor size

Post by Bill Shields »

A 3 hp single phase motor is not the best of ideas.

If necessary get a VFD and run a 3 Phase motor on split phase 220.

As to it being enough HP..enough has been said already. I have an old SB clunker with a 3 HP motor on it...and it is marginal.
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Steggy
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Re: motor size

Post by Steggy »

Bill Shields wrote: Fri Feb 12, 2021 10:21 pmA 3 hp single phase motor is not the best of ideas.
Not only that, such a motor will be significantly more costly than a three-phase motor of the same power and will wallop the power line at startup.
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Harold_V
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Re: motor size

Post by Harold_V »

BigDumbDinosaur wrote: Sat Feb 13, 2021 12:50 am such a motor will be significantly more costly than a three-phase motor of the same power and will wallop the power line at startup.
The inrush current for motors can be mind boggling.
I've posted before on the motor/generator induction melting system I've returned to service. They were the systems built before the third generation (solid state) of induction units were available.

Mine is a 50 kw supply, which operates on 240 volts, three phase. At full load, it draws 190 amps. However, on startup, it draws right at 1,490 amps, and does so for six seconds (verified by our power company). The motor/generator starts free of load, but it's a 3,500 rpm affair, and is exceedingly heavy. The load is so severe and prolonged that I have blown fuses on the primary side of our service, which is 400 amps.

I heartily agree that single phase motors are not a great idea--especially when they are larger than one horse.

H
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pete
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Re: motor size

Post by pete »

I'd sure agree with what everyone else has said.Without a top condition OEM motor and I already had a free one on hand? First I'd look at what head stock bearing type you have. The original and available motor speed is also a good indicator. It's original lathe motor was very likely much lower rpm than today's comman off the shelf single ph motors. Lower rpm rated single ph can still be bought, there just not that easy to find or all that common. But that lower rpm isn't really an option especially with a sleeve type bearing set up if that's what your lathe has. And motor drive technology has moved on by light years. The older motors lb for lb have I'm convinced better low end torque than the much more lightly built motors have today. But to actually re-motor any lathe today? I'd never even contemplate using any single phase motor. At best it's a convenience to be able to plug into any wall outlet.

At 3 hp or above? Not a hope I'd ever go with single ph motor. Even if I had to run a dedicated 220 V line in I'd 100% and always chose a 220v single ph in and 3 ph out VFD/motor set up for any home shop sized machine. There's literally every reason to do so other than a slightly higher initial cost to go that route. In an equal top condition scenario, sleeve bearings that a lot of the older machine tools have are surprisingly a more accurate and rigid system than any roller type bearings are. But that top condition is the operative requirement. And the exact oiling system design dictates it's maximum rpm. Fwiw the worlds most accurate lathes still use that bearing type today. But they also use a temperature controlled and pressurized oiling system to do so. Almost for sure that lathe has a back gear, so for larger diameters, threading etc a VFD might not be quite as important as on my lathe that doesn't have one. But there's still numerous reasons a VFD is still better in every way. How you foresee using the lathe as already mentioned is important. There are now constant torque VFD's, but without seeing your exact situation my guess is a 220V 5 hp motor and VFD combination would do everything you'd ever want. A 3 hp just might be good enough, except if you find it isn't. With larger lathes there's a lot of HP loss just due to frictional drag. And you really can't add HP and torque later. Carbide tooling as mentioned does like higher to much higher surface speed, using frictional heat to plasticize the material is just part of how it works. In a home shop? If you just can't get that rpm for the bearing type you have then the HSS tooling that worked a 100 years ago works just as well today. Any machine tool is always a design compromise, you work within it's design limits of what you have and what it can do.
shootnride
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Re: motor size

Post by shootnride »

Harold_V wrote: Sat Feb 13, 2021 2:42 am
Mine is a 50 kw supply, which operates on 240 volts, three phase. At full load, it draws 190 amps. However, on startup, it draws right at 1,490 amps, and does so for six seconds (verified by our power company). The motor/generator starts free of load, but it's a 3,500 rpm affair, and is exceedingly heavy. The load is so severe and prolonged that I have blown fuses on the primary side of our service, which is 400 amps.
H
This sure sounds like a situation where a Star-Delta starting system, or Part Winding Start motor or a VFD would be advantageous. But, maybe you are already incorporating something to reduce starting current.

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Bill Shields
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Re: motor size

Post by Bill Shields »

VFDs with soft starts go a long way to keeping your electric $$$ under control....
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Harold_V
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Re: motor size

Post by Harold_V »

shootnride wrote: Sat Feb 13, 2021 9:51 am This sure sounds like a situation where a Star-Delta starting system, or Part Winding Start motor or a VFD would be advantageous. But, maybe you are already incorporating something to reduce starting current.
Unfortunately, there has been no provision provided for a soft start, although such a device was offered by Ajax Magnethermic for some of their models.

At some point I have to stop pouring money in this project. It will get indefinite, but limited use, so I hesitate to keep spending, especially at my advanced age.

One of the things I have considered was to extend the shaft of the motor/generator, to which I would attach a powered spin up system, something I'd shop build. If I was able to reduce startup by even a second, that would make a significant difference to the degree of heating experienced.

PUD (Public Utility District), our supplier, installed larger fuses on the primary feed in the hopes that they would be a little more forgiving of the prolonged inrush heating. That was done only after a survey of the possible constant overload of the service, as they must protect the transformers. I am the only subscriber to this feed (it was installed specifically for me), so the load is predictable. While the increase of fuse amperage was only two amps (from 8 amps to 10 amps), it was a 25% increase, so that may have solved the riddle, but only time will tell. The set has been started a couple times without issue, but then that was possible with the smaller fuses, too.

The maker admonishes the user to NOT start the unit more than two times in an hour. That's due to the severe heating in startup. As the generator is excited by the operator, one is admonished to leave the unit running once started if further use is anticipated within the day.

Of interest, this motor/generator is a vertical unit---with only the top end of the shaft exposed, although within an end bearing cap. The cap could be machined to allow for an extension. I'm likely to get back to this project in the near future, as I am ready to fire the furnaces for the first time, a necessary process to vitrify the linings, which are dry rammed within a steel form.

Thanks for your thoughts, Ted.

Bill, I shudder to think of the cost for a VFD for this unit, which is rated @ 75 hp.

H
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Bill Shields
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Re: motor size

Post by Bill Shields »

Soft starts are generally a part of VFD units.

I thought we were looking at a 3-5 HP unit for this unit. Totally missed where a 75 would be used.

Must be getting old since I have no idea of where one would find a 75 HP single phase motor
Too many things going on to bother listing them.
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