<html> Hi Gang! I guess I should chime in on this topic, as I've played around with action centers quite a bit. The wool cloth swells a lot with moisture changes.  This is the main reason action centers are so hard to manufacture so that they work in all climates.  You will find that the most reliable action companies make the centers seem rather loose if you are in a dry climate.  They do it that way so that it will still work in humid climates.  To really be reliable in Florida and Southern Texas, they need to be on the edge of too loose in Alberta! When a wood flange swells with high humidity the action center hole swells also, more so with the grain than across the grain.  Think of it this way: when you have a hole in a normal (non-laminated) piece of wood, the hole behaves like the plug of wood which was removed.  With a large humidity increase, action center holes in the wood get slightly oval if they were drilled when the wood was very dry.  Since the hole is so small, though, this effect is pretty slight. The wool fibers swell in all directions, but the cloth sheet swells in the direction that is easiest to move.  If you wet a piece of wool cloth laying out on a table, it will get a lot thicker and a little smaller in width and length.  Then it will generally stay there after it dries.  If you submerge a hammer in water, it's reaction will depend on how tightly bound together the fibers are.  Soft hammers will bloom out into a fuzzy ball, while very hard hammers will hardly change shape at all.  I once soaked a really nasty hard sample hammer in a glass of water for a week, and after it dried out it sounded pretty good! If you wet wool cloth and place a weight on it, it will swell up slightly and try to lift the weight, then it will shrink back down and (if the weight was heavy enough) the cloth will end up a little thinner than it was before.  Similarly, if you put a hammer into a hammer press and add steam, the hammer will get smaller and harder.  This is how alcohol and water works to loosen a flange bushing.  Because the bushing is bound up by the pin and flange, the fibers try to swell with the moisture (the water does the work, the alcohol is sort of a "thinner" and penetrating agent).  They get squeezed more tightly together and pack the fibers more tightly together, sometimes squeezing out the sides a little! Then when they dry again, the bushing is thinner and works more freely. Sizing doesn't work as well after a certain point, as the wool becomes packed as tightly as it practically can.  If the original cloth was kind of cheap, wet sizing with alcohol and water gives great results, if a bit inconsistent. In theory, action centers in wood parts _should_ react less to humidity changes than plastic parts do, but in reality the difference is so slight as to not be measurable consistently.  I have done some experiments comparing the changes in center pin friction with extreme humidity changes, and sometimes I found slight differences in the change between wood and plastic.  In other tests, I couldn't find any differences, so the tests were just inconclusive. If you want to do some testing yourself, be sure to rebush all flanges with the same cloth before you start, so that you eliminate different cloths and pins as variables. Keep in mind that humidity is only one reason that action centers get sluggish.  In my action center class I talk about all the different reasons that centers go tight, and there is a pretty good list.  Cloth which was not originally glued into the flange in a stable position is one common reason (twisted cloth), as are burrs on the pins. Don Mannino RPT </html>