Originally Posted by mkepke
Have never encountered a wwking machine that required it - unless you have 3 phase power to your shop (ha ha).
There are plenty of machines or workstations that have both 240V and 120V motors, but they all have separate feeds (plugs).
Note that I would co-locate my 240V plugs next to 120V plugs to avoid cords snaking across the shop in all directions. It's annoying stepping around the 240V cord for the lathe, the 120V cord for the lathe's work light, the 120V cord for the lathe's sander...
As Jim mentioned, I too would re-task the neutral wire in the dryer circuit to a ground by marking with green-tape. And I'd replace the dryer outlet with a proper 2+ground 240V outlet. It's just a couple of bucks.
-Mark
Not quite so fast young man, there is a section in the NEC titled- Multi-Wire Branch Circuits. Using four wires: two hots, a neutral, and a ground, you can have both 110 and 220 out of the same double pole breaker. This is the wiring method of choice in my shop. One of the hots passes through DC sensor in panel box. At each location, I have two 110 recpt. and a 220 recpt. Both the 220 and one of the 110 recpt. operate the DC unit. A subpanel is basically a multiwire branch circuit.
As for three phase power, my neighbor has it in his shop, using a rotoray converter I build for him. He has a Bridgeport mill and a Sharpe lathe- what a good neighbor.
Linear Mode
