Glide bolts

[A440A@aol.com]

Antares writes: 
>> We bang on the piano (on the wooden beam that is situated
>> against the iron
>> frame and directly over the keyboard, what is the name?
>> please) and listen
>> for a rattle.....
>> If we hear a rattle we put one finger lightly on each bolt,
>> ubtil we have
>> found the one that causes the rattle.
>> Tighten bolt, end of story.

Greetings,   
    I would caution against this in some situations.  If glide bolts are not 
evenly bearing the load, the action becomes sensitive to climate changes, ie, 
if you have one or two glides that have been turned way, way down, lifting 
the nearest glides off the keybed, lowering those until they just touch will 
leave a lot of stress in the keyframe. The first change of humidity may flex 
the frame and lift the untouched glide buttons farther away off the keybed.  
The next tech will repeat the mistake and so on, until the front rail begins 
to lift off the keybed.  
   Rather than simply tightening the one or two glides that knock, I would 
suggest a gentle lift attempt at the ones that do not, and if they can't be 
easily raised enough to cause a knock, then perhaps raising those glides 
rather than turning the others down would be a better approach. 
   There are also aftertouch considerations when moving glidebolts around, so 
when confronted with a knocking balance rail, I will often raise all the 
bolts off the keybed and adjust from scratch.  If there is a loss of 
aftertouch after all the glides have been evenly mated, it is usually 
possible to turn them all the same amount to restore the aftertouch and still 
keep them balanced in their pressure. 
   I much prefer to set the glide bolts with keys and stack removed, then 
insure a stress free foundation for the action when I mate the stack to the 
keyframe, but this is not something that is always appropos in the field.   
Whatever method is employed, it is important to test with the damper and una 
corda pedals firmly depressed, as the lateral movement and keybed flex that 
results from this will cause one or more glides to lose contact.  Usually 
turning the offending bolt down at this point will not upset the overall 
picture. 
Regards, 
Ed Foote RPT