Yamaha does teach the use of glide bolt adjustment to adapt to aftertouch loss as a result of seasonal RH change. I believe the standard is to have the glides a bit low, so they could be raised if aftertouch increases too much. Hence, on many Yamahas (perhaps most), you will find that raising all the bolts until they are clear of the key bed, and then lowering them until they just contact, will result in a lower key height, and resultant lesser key dip and aftertouch. I think that is the sort of thing Bill was warning against, and it is a reasonable warning.
If you do get into that problem, it can be remedied fairly easily by re-establishing the lower glide bolt position. Once everything is bedded evenly, simply turn all the bolts down by an even amount (45 degrees, 90 degrees, whatever will do the job), and then even out between the bolts in the normal, knocking way.
Rather than the WNG tool, I simply use a 6" rule. I prop/lean it against a key in front of each glide bolt in turn. I adjust the pocket clip so it is just above the keytop (giving a gap of about 1 mm), and then turn the bolt in either direction. That tells me whether it is contacting, and whether it is low. Assuming it is contacting and low (meaning the when you back the glide up, the gap reduces), simply continue until the gap stops reducing (you might need to raise the clip on the rule). Turn the bolt a few degrees in each direction to see where the dead on spot is: down raises the key, up does nothing.
Move through each glide in turn. If you made major changes, go through twice, or even three times. Now do the lift and knock testing. Do it again pressing on all the pedals (that flexes the keybed down a bit). I find this method fast and efficient, and it doesn't add yet one more tool to my kit I lug around. I already have the 6" rule, weighs next to nothing, takes next to no space. Yeah, I know, tool geeks need to have the cool tool, and I have my share of those as well. But I don't carry many of them around with me.
This does leave out the problem of the hidden glide, when present. That one should probably always be raised enough initially to be out of the picture (not to the extreme, just so it knocks, so you don't have that far to go in re-adjusting it).
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Fred Sturm
University of New Mexico
fssturm@unm.eduhttp://fredsturm.nethttp://www.artoftuning.com"We either make ourselves happy or miserable. The amount of work is the same." - Carlos Casteneda
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Original Message:
Sent: 03-19-2017 13:47
From: David Weiss
Subject: Bedding the keyframe
When I first became a piano technician the Journal articles written by Bill Spurlock were very helpful For those of you who remember them, they were beautifully written, concise and clear. Sometimes I go back and read them and always find things that I have forgotten.
I was recently re-reading his article on bedding the keyframe. Bill makes the following statement, "turning the glide bolts completely out of contact with the keybed may significantly change the key height. You would have then created needless work of resetting the key height and dip from scratch."
Normally when I bed the keyframe I turn all of the glide bolts up so none of them are making contact, then I turn them down one by one until they are all making slight contact, always going back to recheck the ones I already did. I believe this is a fairly standard procedure. I have not had the experience of completely altering key height and key dip.
I am wondering why Bill issued that warning. Is it really possible that taking the glide bolts very slightly out of contact for only a few minutes could drastically change the key height and key dip? Are others using the same procedure I use?
Note that Bill's article is not about the more complete method of keyframe bedding where you remove the top stack. His method is for use in the field with a piano in reasonably good condition.
Thanks,
David
David Weiss
Registered Piano Technician
(434) 823-9733
davidweisspiano@gmail.com
www.davidweisspiano.com