Lathe HP motor upgrade?

[Chazz]

So, there I was, taking a facing cut off of a 6" dia. x 1.5" thick 6061 round stock to make an adapter plate to mount my 3", 3 and 4 jaw chucks to my rotary table when low and behold, sniff, sniff,    I smell that 'electrical' burning smell.  Quickly, I reached for the E-Stop, oh wait, my 9 x 20 import doesn't have an E-Stop, so I turn it off.   Anyway, after 3 1/2 years my Rong-Fu .75 HP motor bit the biscut!    



 

So after some research, is there anything I should be leeary of by beefing the motor up from .75HP to 1.5HP?

Thanks,
Chazz

[kvom]

Be leery of another Chinese motor.

If you were to get a 3PH motor and a VFD you'd have a variable speed reversing lathe without changing pulleys or gears.

[Chazz]

Actually, I'm looking at 'U.S. Motors' 1.5HP, 220 3 Phase 'Accu Torq' vector drive and a Temco VFD (CF12?) featuring single phase 220 in to 3 phase 220 out + an additional analogue input on the VFD so if the day comes to CNC the Lathe, the motor (spindle) can be controlled by the CAM software.

I was more concerned about the casting, etc with a 100% increase in power.  I did purchase new spindle bearings rated at ~ 8,500RPM with grease and 12,500RPM with 'oil bath'.

Cheers,
Chazz

[Chazz]

I forgot to add, with the VFD, I don't have to buy a big honkin' 100LBS Rotary phase converter!   

Cheers,
Chazz

[andyf]

I'm a bit puzzled. Have you let the smoke out of the motor itself, or just out of the terminal box shown in your pic?

As to power, I replaced an AC 1/3 HP one on my small milling machine with a DC one from a running machine/treadmill, so I could use a simple variable speed drive. The replacement is 2HP, according to its label, which really is overkill. It has had no adverse effect on the mill, but if I tried using a 1" slot drill to chomp out a 1/2" deep slot in one pass, something would give. I don't ask the machine to work any harder than I did with the smaller motor; it simply isn't rigid enough.

Andy

 

[Chazz]

Hi Andy, the smoke was out of both the starter box and motor.  The motor shaft no longer spins freely. 

I'm puzzled too,    I've never seen a 2HP motor run on 115v, unless (depending on the wiring) you are only using 1/2 the motor and actually only getting 1HP?

Here in North America (I think) a typical 115V outlet can deliver 1200watts? and a 2HP motor uses 1500watts? (not an electrican type)

Cheers,
Chazz

[andyf]

Sounds well fried, Chazz.

We get much more oomph out of each 230V domestic socket here in the UK - up to 13A, or about 3kW. Our modern wiring regulations allow numerous such outlets in a ring circuit with a 30A circuit breaker in the "consumer unit"  on the assumption that 30A in total (nearly 7kW) is unlikely to be exceeded.

If my 2HP DC motor, badged "Leeson, Wisconsin" and in much smaller letters "Made in China" really is 2HP (about 1.5kW) output, and due to general losses in the speed controller and motor it actually takes 3kW input, then it is just about on the limit for its socket outlet (and the 13A fuse in the mains plug). But as I said, I only use a fraction of the available power, and the controller incorporates a soft start, so it probably never draws more than 1kW.

  Treat my remarks with caution; like you, I'm not an electrician.

Andy.

[John Hill]

Chazz, I am sure you can draw more than 1500 watts from your domestic supply, typically for things like a clothes dryer and radiant heaters.

But to answer your question, I doubt an increase in motor size will cause you any problems provided you dont work your machine any harder than before. The most likely frustration, in my opinion, will be related to getting the new motor onto the mountings intended for the smaller one.

[75Plus]

Here in North America (I think) a typical 115V outlet can deliver 1200watts? and a 2HP motor uses 1500watts? (not an electrican type)

Cheers,
Chazz

In the US the standard wiring for 115 V outlets is 12 ga. copper wire rated at and protected at 20 amps, fuse or circuit breaker. This would actually handle 3 hp but it would be pushing the envelope.

[kvom]

Actually, I'm looking at 'U.S. Motors' 1.5HP, 220 3 Phase 'Accu Torq' vector drive and a Temco VFD (CF12?) featuring single phase 220 in to 3 phase 220 out + an additional analogue input on the VFD so if the day comes to CNC the Lathe, the motor (spindle) can be controlled by the CAM software.

I was more concerned about the casting, etc with a 100% increase in power.  I did purchase new spindle bearings rated at ~ 8,500RPM with grease and 12,500RPM with 'oil bath'.

Cheers,
Chazz

I can't say I'd want to spin many lathe chucks very fast on a chinese rongfy type lathe.  My 10ee does go up to 4000 but the fastest I've ever tried is about 2500 with a collet chuck.  The motor/VFD combination sounds good. 

[Miner]

Chazz,
IMO a 220 single phase in to a VFD 220 3 phase out to the motor is the ideal way to go. That's the combination I have on a 3 hp Bridgeport clone. Doubling your lathes HP will help a lot on the avalible tourque when turning the rpms down for larger diameter parts for sure. As long as you don't try and take larger depths of cut with that extra HP then there's no differance to the lathe. The extra motor weight might? create a problem with it trying to twist the lathe bed casting more, So maybe mounting the motor seperate from the lathe bed itself may be a good idea. Your bearings might be rated to those speeds, But your really getting into very specialized and super expensive equipment for part holding that could handle those speeds. ANY imbalance at all would be a large problem. Even high quality lathe chucks would self destruct at speeds far less than your bearing limits. Your lathe spindle would most likely explode too. You may not be even planning for any speed increase. But if you are, I'd sure be doing a lot of research.

Pete

[loply]

For what it's worth, not so long ago I bought a 3hp 3 phase motor off eBay, a Baldor one, for about £60 delivered, brand new.

Bought a suitable VFD from a hongkong seller on eBay for about £70 delivered, luckily it didn't get stung for import tax, and got the thing set up with a potentiometer for speed variation and a nice fwd/off/reverse switch.

Was all very easy and runs smooth as you like. I was put off by the expensive VFDs available and took a gamble on a cheap one, certainly works well for now, time will tell if it lasts...

[Miner]

Loply,
You just might have been real lucky. I was just reading a post a few days ago where somebody mentioned some of the real low priced VFDs may or may not work due to some of them having missing electronic parts. I have no way to verify if that story was true or not. Wish I could remember exactly what forum I read it on.

That "nice fwd/off/reverse switch" you mentioned isn't between the VFD and the motor is it? I know very little about VFDs but I do know they don't like any switches between the VFD and the motor.

Pete

[Chazz]

Thanks folks, a few pionts I failed to mention above, I plan to keep the belt system and vary RPMs within the range of the selected speed, for example, facing a piece of 4" round, I'd set the belts for a 1,000RPM then dial the machine down to say, 600 RPM and as the cutter moves toward the center I can turn up the RPMs accordingly (I think  ).

The 'dead' motor ran at 1720RPM and the replacement motor is 1800RPM, although the replaced spindle bearings are rated at 8,000+ RPMs, I'd NEVER try to spin 'er up that much, I'll stick to the stock 2,000RPM thank you very much. 

I am now thinking I'll pay the extra $45.00 and upgrade to the 2HP. 

@Pete et al, as to mounting the motor, the larger dementions prohibit direct mounting, which is fine.  Between the chip tray and the pedistal I have a 17" deep x 32" wide x 3/8" thick piece of steel plate and if my meausrements are close, I'll just need to get an ~ 2" longer timing belt.

I'm still a bit confused about speed reduction and torq loss, this is my (limited) understanding.  If you use a potentiometer (light dimmer) to control RPM then for every increase in resistance (bleed-off of power) you get both a reduction in RPM and available torq.  In a Vector duty motor coupled with a VFD, I have 220v single phase in and like a really, really good Vegas card dealer, (at 100% power) deals 20,000 pulses of 220v to each leg in the 3 phasse motor for a total of 60,000 pulses or Hz.   
Now let's say I want to go 20% slower than 1,000RPM, so, 800RPM, by turning the RPMs down on the VFD, what I'm actually doing is now sending 16,000 pulses\sec\leg @ 220v, thus a reduction in speed and although there will\may be torq loss, it should be very little compared to any resistive approach.

If any of our electrical types care to correct\expand, we're all here to learn and thank you.

Chazz 

[kvom]

You may get less pulses/sec but each one is longer.

On my 3PH Bridgeport motor  I get good torque down to 20Hz, and can easily overspeed to 90Hz.  With 1000 rpm at 60hz, you'd get 333rpm at 20Hz.

Below 20Hz, I use back gear on the mill.  For parting, 1000rpm belt setting will probably be too fast.  If your lathe has a back gear you'd use that, else move the belt.

[Miner]

Chazz,
Just like computers, My electrical knowledge is very limited. From what I've read, And I don't quite understand everything about them, Some of the newer vector drives offer really high tourque levels and at fairly low RPMs. I bought a pretty pricey Baldor industrial rated VFD about 5 years ago. ($1400) At that time I was advised by a Baldor tech. That SOME motors, (not specified as to what motors or types because even Baldor didn't or couldn't pin point for sure.) Anyway they didn't survive with a VFD. If? the motor didn't survive VFD use. It could be specialy rewound by a good competent electrical motor rewind shop specificly for use with a VFD. My 3 hp mill motor is a Taiwan/Asian frame size, So a rebuild/rewire for VFD use if needed would be the only way to go. (About $800 for my motor to be rewound 5 years ago.) It hasn't needed to be done yet or at least so far. Since Baldor do not build a drop in replacement frame size for my motor. I'd have to build an adapter plate to use one of their or other North American built frame sized motors. Baldor did and may still do offer a special motor designed and built to be used as a 100% tested and compatable combination of a VFD and motor that is/was ultra smooth for operation. It wasn't cheap at around $1800 for a 3 hp 5 years ago. But I will say I did really trust the Baldor techs. information. He or his company had nothing to gain with what he told me.

I'm maybe a little paranoid about burning up a motor due to replacement costs. I have a belt change Bridgeport type mill with a back gear. I'll obviously vary the speeds with the VFD, But normally or never go 30% higher or lower on what the normal motor RPMs should be. Low RPMs and extended run time result in really increased motor heat due to a slower cooling fan speed, I can do a quick belt change to keep the motor RPMs fairly high for larger cutting tools like fly cutters or drop into back gear for really low spindle speeds if I was boring large oversize holes with a boreing head. I personally think that a belt drive mill verses a variable speed belt drive type is the way to go if your going to use a VFD on a mill. High RPMs? I really don't know the exact quality of the motor bearings. I'd suspect fairly low quality, So I don't personally think it's a good idea to overspeed this motor too much. A decent spindle speeder from Tormach is about the same money as a motor rebuild and I can get over 8,000 rpm out of that for real small cutting tools and no changes or worrys about my mills bearings or motor.

So, I've added some non topic information for you, But you now know everything I know about VFDs and motors with VFDs. Maybe some of this helps, Maybe it doesn't. Before I bought my mill I spent far more time with my power supplier than what should have been nessisary about what exactly was the best system between Solid state 3 phase converters, Rotary 3 phase converters and VFDs. I never did get a clear cut answer from them. Luckily I decided on a VFD because I knew far less about them then than I do now. If your only dealing with a single 3 phase motor instead of multiple motors on the same machine a VFD really is the best way to go. And 3 phase is MUCH smoother than single phase. I'd think you'll see an immediate improvement in your surface finishes using it on a lathe.

Pete

[Chazz]

@Pete, again my minisquile(sp?) understanding of why some AC motors don't like VFD is due to the design of thev VFD, (in some design cases?) ie one VFD type will use one leg for starting the motor and when the motor hits a predetrermined set-point, passes off power distribution or runninig mode off to the other two legs, that is, the motor is running on 2 of 3 legs.....not good for some motors.

The VFD I'm looking at uses all 3 output legs to start and run, as well, it is programable for a 'soft' start, meaning I can program the motor to 'ramp-up' to 1,800 RPM and take 5~7 seconds, or more, to do so. 

Again, to any sparky types, added, newer and more importantly, corrected info appreciated,
Chazz