There other people here that can be a lot more detail but stick-out changes everything current, amps, voltages.
M.G.
It can have a pretty dramatic effect on amperage.
For example with .072" Lincoln NR 232 (E71T-8) at moderate parameters for the wire, a change from a seemingly reasonable minimum to maximum stickout covers about a 50 amp swing. And with this wire specifically that will dramatically effect the tendency to include slag or not. Additionally, depending on parameters, moving from a reasonable and working longer stickout to a very short stickout can produce gas marking on the face of the weld. I see guys do this on overhead welds fairly regularly.
I can't verify this, but I have read in a textbook that a certain minimum amount of stickout is needed to properly "activate" the fluxing mixture.
bellaru,
As the electrode extension is increased in a constant voltage system, the electrical resistance of the electrode increases, causing the electrode to be heated. As the amount of heating increases, the arc energy required to melt the electrode decreases. Longer electrode extensions may be employed to gain higher deposition rates at a given amperage. When the electrode extension is increased without any change in the wire feed speed, the amperage will decrease. This results in less penetration and less admixture. With the increase in electrical stickout, it’s common to increase the machine voltage setting to compensate for the greater voltage drop across the electrode. In constant voltage systems, it’s possible to simultaneously increase both the electrical stickout and the wire feed speed in a balanced manner so that the current remains constant. When this is done, higher deposition rates are attained. Other welding variables, such as voltage and travel speed, must be adjusted to maintain a stable arc and to ensure quality welding.
All I can say is have two people, one under the hood and one watching or set up a camera on the readout on the machine/suitcase. Start welding with correct wire feed speed and voltage with proper stick out. Watch the numbers with everything done properly. Then start adjusting your distance, in and out. Watch the voltages. If you have amperage shown you can watch it also and see how far it swings. Then really all you have to do is look at the optimal setting as suggested by the manufacturer and look at the differences you've seen and simple reasoning will do the rest, along with Scotts explanation everything should come together.
The stick-out portion of the wire is important because it transmits the current from the welding tip to the welding arc. Generally, the welding tip and gas nozzle are aligned so that the stick-out can be controlled accurately.
While the arc length remains constant when you use a constant-voltage machine, the current you use will fluctuate depending on your skill. The longer the stick-out length becomes, the lower the current output will be. Likewise, if you use a short stick-out, current levels will be higher. You must have consistent stick-out length for a good-looking weld.
Most manufacturers recommend a minimum of 1/2 in. stick-out for 0.045-in. and larger wires. The larger wire diameters require a greater amount of stick-out.
A minimum stick-out is beneficial because the wire can be preheated in a short amount of time. This preheat can help you vaporize any moisture that has gathered in the core of the wire and prepare the wire to be transferred to a molten state as it reaches the arc.
Another factor to consider regarding stick-out is its effect on the gas shielding of the puddle. Excessive stick-out can create a lack of shielding gas covering the weld zone.