Something I have noticed is that my wire comes in two lengths. 12ft and 10ft. The 12ft wire is very springy and hard to bend, I think it is 316 stainless. The 10ft pieces however are easy to bend, and not springy at tall, leading me to believe it's 304 stainless. It doesn't make any difference, except that the 12ft stuff is harder to bend. Make sure when you buy wire that it is 304. They may give you a higher grade but are not really doing you a favor. I bend most of my track by hand, and use a couple pairs of strong needle nose pliers to get what my fingers cannot. The easier to bend the better.
The teeter totter can be problematic on any sculpture because if the marbles are spaced too closely, then while one end of the teeter is down because of the marble rolling over it, the other end is up and will allow the marble that's following to drop out. I fix this problem by having the spiral below to catch any dropping marbles, or a detour around the teeter-totter and then back on to the track.
The tipping arm can be tricky as well. If I do not add a little piece of wire that holds back extra marbles while the arm is dropping a marble from the upper track to the lower track, then the extras will just fly off over the top of the arm.
These are the steps I use to make one:
1) make frame, 1/4" round rod
2) make loop d' loop, make sure it works
3) make track splitter
4) attach loop d' loop to frame, test a little
5) attach track splitter
6) make the track that people will drop the marbles into - the one that leads directly into the splitter.
6) make track that will lead from switch to loop d' loop. All track should be made "on" the sculpture.
7) make next section of track leading from other side of track splitter, about 5 ft of track here.
8) make, then attach tipping arm
9) make teeter totter.
10) make track leading from exit of tipping arm to entrance of teeter-totter. make sure the ball picks up enough speed. Just a little will do, but it won't roll over if it's too slow.
11) attach teeter totter
12) make spiral, then eyeball where it will be, and make the entrance and exit tracks leading into and out of the spiral, OFF the sculpture. this way you can easily get to the critical weld.
13) install spiral
14) make the track that leads from the teeter-totter to the spiral.
15) make the track that leads out of the loop, that will carry the marble that exits.
16) Now make track that starts from the end of the spiral and connect it directly into the track leaving the loop d' loop.
17) make and add spinner if desired
18) bend up a speed bump for the "marbles on track" element. Make sure the marble has good speed for this element.
Add the supports and whatever else is needed as you go. Then you can easily drop in marbles to test it as you build. Adding the track supports as you go also helps keep the track in place once you find where it needs to be. It is held in place by the support, and you can keep bending.
Now final testing. Drop in lots of marbles at once to see where things go wrong, and adjust it. Clean it, and your ready to show it off!
Here's three recent desktops; #25, #24 and #19 respectively.