There are 2 basic ways to hold pieces together so that they can be solder to each other. One way is to wrap them together with binding wire, the other is to tack them. That's where a tacking machine comes in. By running a very high energy, low voltage current between the two pieces of metal, a tacking machine "tacks" (lightly welds) the metals together. A "tack" is not a permanent weld. It's purpose is to hold the pieces together in the proper position for subsequent soldering. If the position of the pieces when tacked is wrong, the tack can then be easily broken and retacked, with no damage to the work. Most work is actually held in the hand when tacking, so getting the right positioning is very easy and accurate. It's a tremendous time saver when soldering settings, hollowware, etc.
When using "fusion type findings" and using the fusion offset pencil option, you can permanently fusion weld earring posts, tie tack nails, lapel pin nails, joints and catches, and any other findings that are available with a fusion nib. These fusion type findings are readily available from any of the leading finding houses that you may be buying from now.
Tacking machines are not stock items (special order) and take about 2-3 weeks to build.
Their purpose is the same, but their power is not. Tack I is a lower power tacker and is excellent for gold and a few other metals. Tack II, on the other hand, is much more powerful and is designed to handle metals that Tack I cannot- platinum, silver, brass, titanium etc.