Lathe HP motor upgrade?

Gallery, Projects and General > How do I??

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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 :scratch:).

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. :headbang:

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. :scratch:
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.

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