Sometime in the early 90's a decision was made to fatten the knife edges for longer life. They're just a little too wide to freely breath and along the way the tolerance would slip and some knife edges would get fatter. I find these sporadically on 90's trems, but overall the knives are still just too wide to float freely. Around 99'/00'' these far too wide edges started showing up more consistently. It was sometime late in 2000' I reported the problem and by early 02' they've gotten the knife down to a fairly consistent .4mm which floats extremely well is the redesigned studs. Occasionally I will encounter a wider knife on an 02' that needs attention but they are infrequent. The real binding ones that will cause an audibly out of pitch return will most likely be found on 99' - early 01' models. The knife edge itself is not only flat but the flat part of the edge is much wider than it should be, the very corners where these planes meet also very sharp, promoting binding. Imagine sticking a box |_| in a V and expect it to pivot freely.
Not sure exactly when, but the tolerances of the V cut into the trem posts [or studs] had slipped. The bottom angle of the V was now smaller and tighter, pinching the knife edge causing binding. They have now corrected the posts and the New Cut posts have a groove cut around the post between the V and the start of the threads (I will start calling them Grooved posts when this is common knowledge). This groove is cut there just to be able to identify the new posts from the old. The new post is redesigned and the point of the V now has a nice U shape relief which is needed for the knife to freely pivot. Posts have never been better and I would recommend changing any old Edge/Lo Pro posts to these new non binding posts. They begin to appear on production guitars sometime mid to late 01'. This was Ibanez' cure to the fat knife edge problem I had reported in late 00'. I had never examined the post close enough to see the change in the angle but it's very easy to see the difference in the V of a new post compared to any old post.
This is an older post on the left and the New Cut post on the right, barely noticeable is the groove around the New Cut for identification, between the V and the threads. It's very tough to see but the bottom angle of the V on the older post is at a smaller angle making the V tighter. You can also see the very 'point' of the V on the New Cut post is much more open and U shaped.
This combination of tight posts and wide knives created problems with tuning stability on these guitars. The angle of the V in the posts is now smaller, while the edge of the Knife is wider, creating pinching of the knife in the V. The *corners* of the knife edge are also sharp, so they are now *biting* into the now reduced V of the post, not allowing the trem to return to neutral resulting in a 90%-97% guitars.
Very easy to determine if all other factors in your system are correct and tight. See section directly above before proceeding and complete each of those checks first. To diagnose, get the guitar into perfect tune, give it a little whammy abuse and then fine tune again. Push down on the bar and let it rise to neutral position. Check tuning, fine tune where necessary. Now pull up on the bar and let it return to neutral. DO NOT push the bar past neutral. Check tuning. If your strings are now all very sharp this is a classic sign of the flat knives and/or bad posts. It should also respond to just touching the bar up or down 1/4" from neutral if you check neutral.
Now, push the bar down and let it rise. Fine tune. You can play and it will stay in tune if the last motion the bar made was rising to neutral. As soon as you pull up on the bar it will return sharp unless you push it slightly past neutral so the bar is on the rise as the last motion. Confused? ;) The trem is not floating right so the neutral you're originally tuning to is a false neutral, but becomes neutral to the trem when the motion is in one direction. Still confused? Me too ;) If you pull up on the bar and fine tune it will act the same way as a second false neutral, but will only be in tune if the last motion is the bar falling, as soon as you let the bar rise to neutral it's flat.
You will need to pull the trem to check the knives. A good knife edge looks like the edge of a butterknife. It is not sharp, and it does not have a wide flat at the edge. See the next section Sharpening Knife Edges for a more detailed explanation.
Flat knife edges alone will cause tuning instability even with the New Cut corrected posts.
Bad posts will cause tuning instability even with good knife edges.
It's difficult to see the added identification groove in the shot above so here's a better shot. Notice that the groove will be cut in a different spot on each manufacturing batch but always between the V and the threads -