Piano World Home Page Forums Our Most Popular Forums Piano Tuner-Technicians Forum Regarding glide bolts

I just want to know if I understand this correctly:

higher humidity - glide bolts go up (less pressure on keybed)
lower humidity - glide bolts exert greater weight on keybed

If my understanding is correct, then here is my question:

IS there a range of regulating glide bolts such that they maintain adequate contact with the key bed during seasons of high humidity?

Pardon me if this is a stupid question.

It is not on all glide bolts the same.

It is not the same with all key frame, while I think you are right with the directions of motion.

Some pianos are really more stable than other. (Steinway for instance, assuming the key frame have not been over tense initially)
Soft key frames too, as Yamaha.
Kawai on RX seem to have a real problem with that, as they instruct to make the glide bolts touching the keybed only at the end of the whole regulation , keyboard leveling included)so glide bolts have about zero pressure on them.
In the end I think that doe not impeach that the extremities of front rail tend to clack during dry season ( they should not as there are pressure screws in the blocks to regulate)

about 1/8 to 1/4 turn (maxi) on the center of the ones that move -
CAUTION !
turning the bolts without understanding the effects can throw your action out of regualtion, or change the tone in a way you do not like, so this is to be one by the rare trained techs capable of doing so.

For instance, lowering them too much in summer may force the keyframe and leave a gap in winter. raise the key dip, enlarge hammer travel distance, at some point make the impact of the hammer too woody or too noisy , modify aftertouch.

Raising glide bolts in winter may not be enough, will lower the keydip and make the tone less full (it is yet during winter due to a sounboard that sound as if less resilient so that plus that may make a less pleasing tone, more bland)

IMHO the real solution (particularly on a piano that have yet some years in the same place, it to make a neat key leveling job taking in account the season. minimal contact in winter, a little more firm in summer.

Of course using the glide bolts to compensate for a keyboard that lowered in mediums due to wear may exacerbates the problems, while a very small margin is available it is not there to abuse )



See also the extreme pressure/deformation can reflect in blocks tightness, I always check the pressure there (one may be able to have the front rail rattling when pushed up, not far from the block)
Surprisingly, older design keyframes of good quality but without bolts, can be very stable, as on Boesenderfer with the key bed hollow shaped.

But I find Sauter, Seiler, other brands, with a huge play under the middle of balance rail after decades.

PS installation of glide bolts on a rigid keyframes is not an option, there is also a difference in tone and touch if the contact under the balance rail is modified for the one of glide bolts.

Best way to regulate hardwood or massive keyframes when lost : without keys, but the stack screwed, and blocks. "paper strips just lightly retained by the balance rail. With the keyweight the pressure will be perfect (and even). Not for softwood keyframes that are often warping high by themselves.

Thank you for your reply Isaac.

I asked this question because on my two year old Hailun 178, NONE of the glide bolts were in contact with the key bed. That is, I took out the keys and put on the action with blocks, and ALL SEVEN glide bolts allowed paper to slide freely underneath. I already adjusted them with the paper method. Not easy at first to distribute the weight evenly, but I was successful after five tries. Whew! As you said, there is a significant improvement in tone and touch. More notably, I find that I can make a melody line sing better on my right hand while comping with my left. Key height is 65 mm and aftertouch is just right.

While I was regulating I took note of RH which was around 50%. In my place the RH would go as high as 80% and I wondered if this would affect the glide bolts.

Thanks so much for your reply.

A quick way to check if they are too tight is to lift the stem of the glide bold by grasping it with the fingers and pulling upwards. It should knock with very slight lifting and sound solid when the stem is returned to normal. Check all of them with the cheekblocks screwed in and well adjusted so that the front rail only just doesn't knock in their vicinity.

If you have to make large adjustments, check adjustment of the chrekblocks anyway. Even with adjusters on the cheek blocks, I always knock on the key frame and push pn the cheekblock back and forth when tightening them so that I don't over tighten.

I don't rely on shoulds and shouldn'ts where humidity is concerned with pianos. They can be quite contrary. Just check things at every opportunity such as every tuning and you will eventually find a spot where everything works fine all year unless the piano has to endure great extremes.

Thank you, rxd!

Rxd, I consider the thumb and finger method to be perfect for Steinway and some others, but for instance on Yamahas it is too easy to hae a rattle,

As I see it it depepd of the global equilibrium of the action, so depends of the way mass is is distributed front/back.
SOr for Yamahas, I raise the stack and "feel" how is the weight evened at the glise bolt level by ascertaining how much force up is necessary to have them tapping

PS What I mean is that on Yamahas they can tap "easily" with the fingers while being too much forced.

They can be screwed by tone on those pianos, too, tapping on the balance rail and stopping the rattle.

Great to read you noticed better tone an touch Electone, it is real sign of success with that not so easy regulation (took me 6 months daily training to begin to perceive more finely the glide bolts)
There are also different methods, more holistics may be, to check the glide bolts.

I wonder if in your case, depending of the time frame of the humid season, it would not be better to shim temporarily under the glie bolts with an adapted layer of suitable material, a paper/mylar of the good quality, not sensitive to moisture. Just there uring the humidity rise, so you dont threw off your regulation.

??

Ah. Yes, true with Yamaha and that reminded me that some Japanese pianos, possibly others have a hidden glidebolt. Be sure to look underneath the keyframe.

I was taught to do all the regulation of an action with the center rail glide bolts turned up enough that they do not contact the key-bed. Then bed them at the end of the process.

I think it is possible of course, but see it more as a security. On a Yamaha, for instance, I think that if you do so, you have raise the key level when regulating the glide bolts, if not you have rattles, insufficient firmness.

SOme of the regulations cannot be done as finely in my opinion, if the balance rail is allowed to flex at each activated note.

You mean, on a bench, or in the piano ?

I always have the bolts touching , even regulated "tight" in some pianos, but do most of the regulations in front of the piano.