Repowering a Lathe

O

OrangeAlpine

Active User
H-M Supporter Gold Member
I have an Enco 12 x 36 and the motor has always been prone to acting up with strange buzzes, hums and sometimes refusal to start. Lately, there has been a strange hum while running at speed. I think it is time to consider repowering.

The current motor seems to be 1 1/2 hp (7.11 Amps, 220). 1140 rpm. Pulley sizing gives 1/2 spindle speed when the belt is on the small motor pulley. Max spindle speed is 1200. Here are my issues:

HP requirement. I have a 1 hp DC motor that I am considering using. I always thought the lathe had excess power and the 1 hp would be okay. But when I upgraded the 4 jaw chuck, the motor really had to work to get up to speed on the higher speeds. The old chuck weighed 32lbs, the new one 38. I know the DC motor would start at zero rpm, so starting effort is not critical, but it does give some insight as to how hard the motor is working. Anyway, any thoughts or experience on power requirements?

Motor type.
Replacing with a 220, 1140 rpm motor seems a waste. They are expensive and really have little going for them other than they power the lathe at the correct rpm.
DC with PWM vs. 3 phase with VFD. I have zero experience with both. What's to consider?

Motor rpm.
The DC motor I have is 2400 rpm so I could belt it up using the small motor pulley and have a max spindle speed close to OEM. Three phase with VFD is a different ball game as the speed variation is plus or minus motor design, so I see no real value in an 1140 rpm three phase. I'm thinking an 1725 rpm motor would work better. Maybe 3450?

Bill
 
Bill:

Why not consider just taking the old Enco motor to a motor repair shop and get it looked at. They probably can bring it back to new specs at less cost and effort than changing out. I had problems with the motor on my milling machine and I found a motor rebuild shop in town and they did a great job at about half the cost of the new motor if I could have even found it.

Just a thought
 
as a point of information a three phase motor will run smoother than a single phase motor for the same given application, the power impulses are 120* apart. there are 3 phase motors that run at 1200 rpm's , as an option.
there is nothing really to a DC motor. they are easy to repair.
you, with a little patience, i'm sure can replace bearings and brushes if so equipped. most other repairs and testing are easily accomplished.
the only real issue for a home shop would be to rewind the motor, or make repairs to the rotor.
in either case your motor wouldn't run if the rotor or windings were damaged anyway.

i'm a three phase fanatic, take my words with a grain of salt.
DC is cheap and easy to control and a great choice for certain applications.

you'll have a difficult time in managing the lathe speed at 3450 rpm ...way too fast, speed reduction would be a prerequisite.
 
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ML_Woy said:
Bill:

Why not consider just taking the old Enco motor to a motor repair shop and get it looked at. They probably can bring it back to new specs at less cost and effort than changing out. I had problems with the motor on my milling machine and I found a motor rebuild shop in town and they did a great job at about half the cost of the new motor if I could have even found it.

Just a thought
Click to expand...

The Siren's song of variable speed is hugely attractive. But mostly because I've always heard the Chinese motors are, in general, a disaster. But maybe that's just part of the general slam against Far East machinery and is as unwarranted as the statements that as machinery, they are ****. I don't know.

But at this stage, I'm open to everything.

Bill
 
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I guess it depends what criteria we're using for a recommendation. If budget is critical, you do own the DC motor. But I think you might find it not able to keep up with a lathe that size. Depending on what you cut etc. I suppose you could rebuild the current motor but unless it is an oddball frame size or some other factor that it makes it worthwhile to keep it, I rarely see the value in rebuilding small AC motors anymore. That leaves a new AC motor. Single phase 1-1.5hp 1700 rpm motors are fairly reasonable in standard frame sizes, if you do your homework. Plus it will be a fairly straightforward install if that is a concern. What is your objection to a 3-phase with VFD? 3 phase motors run smoother and more efficiently than single-phase. Plus the VFD gives you variable speed and so many more options. I just installed a brand new Baldor 1.5 hp 3ph (for $230 on ebay, $700 msrp due to odd 204 frame size) and a Teco 2hp 7300EV VFD for $160 in my Hardinge and it runs so smoothly and literally modernizes a machine all on it's own. You can generally use the existing switches and task them through the VFD. These things have not become so wildly popular by being impossible to install and set up. They are extremely user friendly and I think they actually simplify the entire motor retrofit process.
So those are the options. I vote for the 3ph with vfd!

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I'm not looking for recommendations as much as information. The pluses and minuses of each installtion, but especially hp requirements. As an example, I would not consider a single phase 1725 rpm motor. It would require a complete redo of the pulley system in order to get workable speeds. Not so with the other options. Also, I do not want to lash together a setup that would result in potentially dangerous overspeed. Not so much for me, but future owners.

BTW, I have nothing against VFD, that's why it's in the mix. Don't have any experience with VFD or DC, so I'm seeking information from those that have. At the moment (good at least until this is posted) , I'm thinking that if 1 hp is considered adequate, I'll have the DC motor checked out and get another controller.

Bill
 
I have a VFD on my lathe - mostly to get 3 PH power, but I find myself routinely using the VFD for speed ranges even though the lathe has a mechanical variable speed feature built into it. If my 3 ph motor ever goes south, I will consider a DC motor replacement and remove the mechanical drive feature.

I have to agree with other responders - that you need to convince yourself that 1 HP is enough for a 12" lathe before you go the DC route. But, if most of your work is in the 6" OD and less range, the 1 HP might be a good candidate.

It might be worth doing a little more research on the DC motor before you make a decision.
One way to determine the load on the existing AC motor is to use a clamp-on amp meter to measure current when the motor is under load.
The % running amps of full load amp rating (FLA) is close to being proportional to the HP output of the motor. For example, 9 amps on a 10 amp, 1 HP rated motor =~ 0.9 HP. But - the motor is already acting spooky, this may no longer be a reliable way to estimate the HP.

The biggest benefit of DC is that you get full torque right down to 0 RPM. (Even the good VFDs lose torque as you go down in Hz).
(Monarch lathes have used DC drives since the 1940's to get variable speed with good low end torque).
The low-cost, current feedback type of DC drive gives fairly good speed control for home hobby machines - comparable to a VFD.
The cost of a DC drive is comparable to a VFD, maybe a little higher.
There are several types of high precision speed control DC drives available for a lot more $, but for home use, I am convinced that the simple DC drives are adequate.

DC motors typically come in 90 VDC ratings for use with 120 VAC drives, and 180 VDC for use with 240 VAC drives.
The motor name plate will tell you the VDC and Amp DC rating and therefore what type of drive is needed. The speed given on the name plate is the "base speed." The drive does not care what the DC motor speed is as long as the drive can deliver the amps that the motor is demanding. You get about the Base motor speed at rated armature volts and amps and rated shaft HP. (EDIT - so with a 2400 rpm rated motor, you may be able to use the existing 1/2 speed pulleys.)
The name plate will also give a "Field Volts" and "Field Amps" rating if there is a wound field. If there is a field rating on the name plate, you need a drive it with a field power supply - most DC drives have this option available or already built in.
Some DC motors have "permanent magnet" fields which do not require a field connection.

The only downside I see to DC motor systems is that there is eventually brush maintenance. But, for us hobby users, I would think it takes years of use before this becomes a concern.

Sorry to ramble on. Hope this helps,
Terry S.
 
I know this isn't an answer to the original post, but more of a question about the required HP, like was mentioned in the last posting. I have a 2HP 3-phase Clausing 5914 that I'm fixing up. At this time, I'm borrowing a friends rotary phase convertor and everything is working fine with the speed control on the lathe. (a nice wide range of speeds). I was wondering about buying a static phase convertor, which would yield about 1.3HP. Are there any other drawbacks to using a static convertor? I'm on a tight budget and Clausing parts are eating it up quickly, so the Static convertor option is looking good.

Jack
Fort Loramie, Ohio
 
His
jmhoying said:
I know this isn't an answer to the original post, but more of a question about the required HP, like was mentioned in the last posting. I have a 2HP 3-phase Clausing 5914 that I'm fixing up. At this time, I'm borrowing a friends rotary phase convertor and everything is working fine with the speed control on the lathe. (a nice wide range of speeds). I was wondering about buying a static phase convertor, which would yield about 1.3HP. Are there any other drawbacks to using a static convertor? I'm on a tight budget and Clausing parts are eating it up quickly, so the Static convertor option is looking good.

Jack
Fort Loramie, Ohio
Click to expand...
I guess my question is why? Why would you opt for a static converter over a VFD? Price isn't much different for either, from what I know. A 2hp Teco VFD can be bought for $145-175 depending on model. I think static converters are in the same range? Aside from the drawback of losing 30% of the power, you can't run the motor for lengths of time due to overheating concerns and multiple restarts within a short period of time are also an issue. These factors make me question the amount of stress the converter is placing on the motor. You're not saving money if it ruins the motor in a couple of years. Unless something has changed that I don't know about...I would go either vfd or spend the money and do a rotary converter. This will work for you.
http://dealerselectric.com/item.asp?PID=4554&cID=0&scID=165
I own two of the higher level model of the same drive #JNEV 202H1and they work awesome.


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My DC motor (PM) is labeled as follows:

Volts DC 115

Amps 8

I found a KB Electronics Controller on Ebay, about $75. Model KBIC-240D. I think it would serve my purposes, but would someone in the know please check? Electronics is a foreign language. I found this little ditty on Page 7 of the manual and find it a little distrubing.

CAUTION!
Consult factory before using on constant horsepower applications such as saws or drill
presses. Do not use in explosive atmosphere. Be sure the KBIC
®
is used within its maximum ratings.


http://www.kbelectronics.com/manuals/kbic_manual.pdf

Anybody have any idea what the constant hp caution is about?

Bill
 
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