220 = more water
Richard---
I remember asking my father that very same question when I was young. Let's see if I can explain it.
Your motor is developing 1HP. In order to do that, it has to draw a certain amount of electricity (measured in W, or Watts). Now I have no idea what the Wattage of your 1HP motor is, so I'll just use 1100W as a guide.
According to classical electronics (assuming total power transfer without a reactive load, for those of you out there who pay attention to such), the power (in watts) delivered by a source is equal to the product of its voltage (in Volts, V) and its amperage (in Amperes, or Amps, A). Therefore, if you have a 110V source providing 10A, you have (110*10)W, or 1100W.
Now, let us take that same concept with 220V. If you have a 220V source providing 5A, you have (220*5)W, or 1100W.
The difference?
Wires and outlets are rated not only by voltage, but by amperage. As a general rule, the thicker the wire, the more amperage it can sustain. Here's why:
Resistance is measured in Ohms, and is defined as the quotient of the voltage drop across an element divided by the current through it. It is a fact of life that only superconductors are lossless, and anything else will have some sort of electrical resistance. Standard conducting wires will have lower resistance if they are thicker (imagine a water pipe: water flows more easily in a 2" pipe than a 1" pipe). Let us make an example using 100' of copper wire (larger gauge numbers are thinner wires)
12 gauge: 0.187 ohms (pretty standard for in-wall wiring)
18 gauge: 0.751 ohms (pretty standard for VCR's, etc)
Now---it is another fact of electronics that the power dissipated (in Watts) by a resistor is equal to the square of the current flowing through it (in Amps) multiplied by the resistance of the resistor (in Ohms). In any resistive element (wire, resistor, light bulb, etc), this results in heat. Using this equation, we discover:
1100W load, 110V source:
12 gauge wire: 18.7W
18 gauge wire: 75.1W
1100W load, 220V source:
12 gauge wire: 4.7W
18 gauge wire: 18.8W
So what does this mean?
Basically, if you have a device that can be wired for both 110V and 220V, and is wired for 110V, you will need thicker, heavier wire than if the item is wired for 220V.
I would recommend that you check the power requirements of your lathe. If you need more than 10A at 110V to power the sucker, I would encourage you to wire it for 220. Besides, having a 220 run to your (I almost typed shack---can you tell I'm also a radio amateur?) shop may prove handy should you discover you need a piece of equipment that requires 220V.
Good luck, and I hope it helped,
Henry C. Gernhardt, III