10:48
@Pᴀᴜʟsᴛᴇʀ2 14-30 is a 120/240V connector, while 6-20 is a 240V connector. So you'll just ignore the neutral from the 14-30.
Make sure you use a cord that's sized according to the welder manufacturer's instructions.
And make the cord as short as practical
Or, if you want a really long cord, make sure you size it up appropriately.