KS 10: Bedding the Balancerail

KS 10: Bedding the Balancerail

There are three principal styles of grand keyframe balancerail - the stiff, Steinway/Mason & Hamlin style supported by adjustable glidebolts, the more flexible Asian style with glidebolts plus hidden glidebolts for action elevation, and an awkward alternative with no glidebolts. In all three cases, the balancerail fit can be affected by any of the previous steps being off. So first steps first. And in all cases, adjust with no pedals for bench setup and with pedals for the final in-piano steps. 

Old way: The traditional trick of turning each glidebolt to just let a strip of newspaper be pulled from underneath without tearing works pretty well, certainly as a roughing in of the fit. But the procedure works best with keys off and topstack on (in case it affects keyframe shape). This represents extra worktime since sampling needs the keys back on, and returning to the piano from the bench will require them off for the with-pedals touchup and back on to finish the regulation.

Newspaper will rip in a straight line without pre-folding. Make a strip about half-a-page long and an inch wide. Then, cut the end to 45-degrees for reaching under the bass end glidebolt (because it's right beside the action stoprail and keyframe structure forces an angled access). Lift the keyframe, slide the strip under the glidebolt, let the weight back down, and adjust the glidebolt to just release the newspaper without tearing it. All the glidebolts must be up first, of course, and the return spring out. Then, proceed one after another. This strategy guarantees weight of the keys will complete the bedding and glidebolts will be well-balanced.

Another commonly used method of balancerail bedding involves thumping on keypins/buttons with the fleshy part of one hand while lifting and lowering the fully-assembled, cheekblock-bound action to gauge glidebolt contact with the other. This requires considerable strength and skill. But, well-done, it is fast.

New way: Use a WNG Keyframe Bedding Tool (with action fully-assembled and cheekblocks in). This dial indicator, pinched vertically between two adjustable set screws (to accommodate different size action cavities), sits on key button, cutaway clearing balance pin, and bears with plunger on pinblock above. Since the pinblock won't shift, this gauge indicates movement or no movement in the balancerail. With glidebolts retracted, lower them one-by-one to touch down, moving the needle, and then eliminate indicator motion.

You can leave the Bedding Tool where it is and turn the neighboring glidebolt to just move the indicator and then back up to just not move it. Using this one-and-next-one technique, quickly set them all to just no-motion. Then validate one-to-the-next-to-the-next, pushing lightly on each glidebolt for no indicator movement. 

With unfamiliar keyframes, particularly containing a long, glidebolt-free section, pull the action out for a look at its underside. As with this Baldwin action, there may be a glidebolt that doesn't show from above, forcing removal of a key to complete the bedding.

Again, no pedals on the way out to the bench but with pedals back in the piano to finish up, as pedaling will lever the keybed into noticeable deflection.

In flexible keyframes, leave hidden glidebolts where they are to maintain action elevations unless good reasons require a reset. Back up the rest of the glidebolts to clear the keybed and proceed to eliminate motion in each with the method suggested above. 

Next week: Bedding and Action Elevations

(Index of all articles in this series)



Alan Eder

Excellent series, Chris! Thanks so much for sharing the benefits of your considerable experience with the rest of us. In the case of a keyframe with hidden glide bolts, how does one determine whether or not the hidden glide bolts protrude the amount that they should before proceeding to bed the other glide bolts? Best, Alan

Alan Eder
Mike Dugan

Wonderful information! Thank you for sharing.

Mike Dugan

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