jbeech
rrAdvertiser
Location: Sanford, FL (Orlando area)
| This is explained in Addendum v1.7 - but in short - what's likely happened is there's play in one of the seesaw arms. If I had to bet, I suspect either the screw securing the seesaw arm onto the shaft going into the seesaw has backed out slightly, or there's a ganging of tolerances which has resulted in a loose fit on one of the arms. Checking for either condition is actually pretty easy.
Here's how - first, grasp the seesaw arm between your thumb and forefinger and give it a side-to-side wiggle. Next, rotate the head around and check the other seesaw arm the same way. Dollars to donuts there's more play in one versus the other! The usual cause is the bolt has backed out a little. Alternatively, there's a slightly greater amount of freeplay due to a ganging of tolerances. This just means the seesaw arm itself, either of the the two ball bearings, and/or the shaft itself (which the seesaw arm rides) on has a slight difference in fit. The solution is simplicity itself.
First, try tightening the bolt. Be careful though since this bolt threads into the plastic seesaw. Fortunately, if you strip it out, all's not lost. Just use a little plastic-type CA as thread locker and you'll be back in business because you can pretty much restore the threads this way. If the damage is too bad, then fortunately, the part is very inexpensive so it's not that big a deal.
Anyway, if that's not it, then back the bolt out and look to see if the shaft itself (the one the bearings ride on) isn't just a hair too long (you'll see it sticking out past the inner race of the outer bearing of the seesaw arm - it's pretty easy to discern). If this is the case, then next, using a jewler's file, just file down the end of the shaft down a few thousanths (or however much is needed to make for a perfect fit).
This process is called "blue printing" and top pilots engange in this on every assembly of a machine - and we explain how in the addendum sheet included with the Tiger 50 . . . remember, the addendum is what we learn since I wrote the manual (back in March of 2004). Granted, most of us aren't top pilots, but blue printing assemblies is a simple and easy (and free) modification. What's more, it can occasionally result in a tangibly better handling machine and it's fun to do (after all, this "is" modeling).
I placed a section on blue printing seesaw and mixing arms in the addendum because while you may check the fit and find everything perfect, the fact is that occasionally it's not, and blue printing let's you make it better (and of course, parts can wear also). Usually this ganging of tolerances isn't an issue but sometimes it works out against us. What's this mean?
Simply this . . . it's surely no surprise that two bearings with the same part number can actually vary slightly in dimensions, right? I.e. you can measure them both and by using instruments of sufficient precision will almost always discover that one can be slightly thinner than the other, similarly, the ID and the OD can vary slightly as well. The same holds true for the shaft - such that it might be slightly longer than others in the same parts bin. Nonetheless, these differences are within the +/- tolerances of the design. What happens sometimes is that during assembly, a thinner bearing and a longer shaft got matched up - which results in too much play in one of the seesaw arms. The process is refered to in the industry as a ganging of tolerances.
Naturally, the opposite can also happen, but in the case of the seesaw arm assembly a thicker bearing and a shorter shaft, while they can also come together during assembly, don't usually cause a problem. Why not? Because for this assembly, it's the loose fit that can cause a blade to flutter while the tight fit is felt as the screw being tight so you stop tightening it, understand? The flutter can easily be strong enough to lead to a spindle shaft bending. Fortunately, these are sacrificial parts and hence, are cheap and easy to replace. I hope this helps.
John Beech - GM (and janitor)
Audacity Models |
