Although the serial port connection to the K3 does not require soldering (to the K3), other models do require soldering.
Readers might find this device useful:
http://www.dansworkshop.com/2008/03/smt-hot-air-pencil/
For a high current, low voltage, power source Dan uses the transformer from a micro-wave oven, with the high voltage winding cut away and a new, high current, low voltage, winding added.
Lots of information on the 'net about doing that for "DIY welders".