<html> <body> Hi Dave,                     You seem to have a good grasp on what is happening. To illuminate the picture;   For argument sake. With a 4mm hole the key feels free, travelling through 5 degrees of arc, with a 7mm hole you start to feel resistance at the 3 degree point. and a firmer push is required to push the action through let off and after touch. The binding makes it difficult to feel let off, and makes even touch almost impossible  Both Korean manufacturers have tended to over ease the keys to mask the problem. leading to a noisy action, from chucking keys. After reaming, I have often had to steam the balance rail hole, because the hole had been over eased, masking the hole height problem Seen the same gross problem in the recent Chinese pianos. Now for the funny:     I have carried the reaming tool around for about 20yrs, and only used it when I did various balance rail hole repairs.   In the last 12 months I think I have almost wore it out. ;-)  I have hardly used my Yamaha easing tool on any thing but Yamaha pianos. Regards Roger <blockquote type=cite class=cite cite="">  Thanks for the detailed response.  Very interesting stuff.  I'll have to get a 4mm reamer and try this out.  You've done all of the legwork already!   If I'm reading this right, what's happening is the key is not rocking correctly at the pivot point/balance rail due to the overly tall hole, which essentially means the key is acting shorter than it really is...right?  And manufacturers have counteracted this by increasing dip to 11mm...?    I think I'll buy a Seiler just to experiment with in my garage....:-)   Thanks again!  Your generosity is always appreciated!   Dave </blockquote></body> </html>