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Joined: May 2015
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I need to make the let off closer than the 1/4" that most of the bass keys are at on my grand piano.
I looked at the action, and for most of the first octave, and some of the second, the let-off screws are maxed out, and cannot be turned and raised anymore.
I was told thinner regulating punchings may be required, but
is there anything else I could try?
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The most likely thing is the hammers are worn down to where the action is not capable of being properly regulated. Time for an action rebuild?
Last edited by Ed McMorrow, RPT; 05/06/15 04:44 PM.
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The most likely thing is the hammers are worn down to where the action is not capable of being properly regulated. Time for an action rebuild? Thanks for responding. The hammers were replaced not too long ago, so this in not likely. Besides gluing thinner regulating punchings in there, has anyone tried removing the let-off buttons, and sanding the wood side down about 1/16"? In any case, I am aware I will need to check the hammer drop afterwards.
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Do I understand correctly that the hammers were replaced recently but the action was not then regulated to suit the new hammers?
Dorrie Bell
retired piano technician
Boston, MA
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Do I understand correctly that the hammers were replaced recently but the action was not then regulated to suit the new hammers? I doubt it, because the rest of the notes, from A2 on up, have about 1/16" let-off, so they appear to be adjusted correctly. The cross-strung bass strings obviously have to be higher than the other strings, so that's where the problem is, and the let-off buttons there were already maxed out, so whoever last regulated it no doubt saw the problem. Too bad there doesn't appear to be an easy way to raise the entire let-off rail as a whole....
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The hammers should have been bored so that the length from the tip to the bore for the shank is the same for all notes. This requires boring to a different length in the bass, longer on a grand, shorter on a vertical. If this was not done reasonably close to the proper lengths, that may have to be corrected.
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The hammers should have been bored so that the length from the tip to the bore for the shank is the same for all notes. This requires boring to a different length in the bass, longer on a grand, shorter on a vertical. If this was not done reasonably close to the proper lengths, that may have to be corrected. Good point. The grand bass hammers appear to be only slightly higher than the other hammers, but it's certainly not as obvious as the difference on my upright piano. I've replaced hammers, but I don't feel like re-doing all these if they were incorrectly installed. Maybe I'll sand the let-off buttons down 1/16", and glue on thinner punchings. That in itself will be a bit of a chore!
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Remove the action. Measure the distance from the keybed to the string at each end of the bass section and record those values. Measure the height of the hammer shank flange center pin from the keybed. Subtract that value from the string height, and that will tell you what the hammer bore should be.
For the end hammers in the bass, measure the distance from the crown of the hammer to the center of the of the hammer shank as it passes through the hammer molding. That tells you what the hammer bore is for those hammers.
Compare what the hammer bore is to what the hammer bore should be. If the hammer bore of the drilled set is short by a decent margin, then the your regulating screws will max out as you describe.
What make and size of piano is this? I once bored a set of hammers for a runt grand where, in the bass, the string height varied by almost 3/8"!
fine grand piano custom rebuilding, piano technician and tuner
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What William said. Don't ruin the action by trying to take the lazy way out. Remove the hammers of the bass section and the rest that can't be properly regulated, replace or rebore the existing with the correct bore distance and properly regulate. Do it once, do it right.
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Easier way to tell if the hammers are bored incorrectly: Place a straightedge against the tenor strings from below at the strike point, and measure from that to the bass strings at the bass break. That should be the difference in the bore distance between the bass and tenor hammers. A similar method works for verticals.
Some pianos have a bar at this point, so you would need a straightedge with a cutout for that.
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We already have something of a visual clue in that the bass hammers don't seem much longer than the tenor ones. Given what appears to be a slovenly job, there is no reason to assume that the tenor or treble hammer bores are correct, although they at least appear to be able to be regulated. Is there also an error in bore distance in the tenor and treble, and if so, how much?
It would take less than 5 minutes extra to measure several locations in the plain wire sections to determine what their string heights are. Collectively, one can then decide on an informed course of action.
If the hammers are taken out to be plugged and then rebored to the correct dimension, one must make note of how much hammer molding is then left for the tail length. Sine we are likely boring the hammers to make them longer, if that amount is substantial, then a radical foreshortening of the tail length will have consequences in the regulation that must follow. The question is then, can I rebore, or is replacement of the hammers the only viable option?
fine grand piano custom rebuilding, piano technician and tuner
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We already have something of a visual clue in that the bass hammers don't seem much longer than the tenor ones. Given what appears to be a slovenly job, there is no reason to assume that the tenor or treble hammer bores are correct, although they at least appear to be able to be regulated. Is there also an error in bore distance in the tenor and treble, and if so, how much?
It would take less than 5 minutes extra to measure several locations in the plain wire sections to determine what their string heights are. Collectively, one can then decide on an informed course of action.
If the hammers are taken out to be plugged and then rebored to the correct dimension, one must make note of how much hammer molding is then left for the tail length. Sine we are likely boring the hammers to make them longer, if that amount is substantial, then a radical foreshortening of the tail length will have consequences in the regulation that must follow. The question is then, can I rebore, or is replacement of the hammers the only viable option? Well said! 
Keith Akins, RPT
Piano Technologist
USA Distributor for Isaac Cadenza hammers and Profundo Bass Strings
Supporting Piano Owners D-I-Y piano tuning and repair
editor emeritus of Piano Technicians Journal
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Remove the action. Measure the distance from the keybed to the string at each end of the bass section and record those values. Measure the height of the hammer shank flange center pin from the keybed. Subtract that value from the string height, and that will tell you what the hammer bore should be.
For the end hammers in the bass, measure the distance from the crown of the hammer to the center of the of the hammer shank as it passes through the hammer molding. That tells you what the hammer bore is for those hammers.
Compare what the hammer bore is to what the hammer bore should be. If the hammer bore of the drilled set is short by a decent margin, then the your regulating screws will max out as you describe.
What make and size of piano is this? I once bored a set of hammers for a runt grand where, in the bass, the string height varied by almost 3/8"! Thanks for the explanation. This paper clarifies it even more: http://www.spurlocktools.com/index_htm_files/Hampubpdf995.pdfI just had a master piano tech look at my piano, and just by looking at it, he felt the bass hammers were correctly bored. Stunningly, he actually recommended doing what I was thinking: raising the let-off rail. He suggested this because the several let-off buttons that were maxed out were in the center of the rail, while the outer sides still had room. Also, the center of the rail is attached with a small metal L bracket. He suggested I remove the bracket, plug up the hole with epoxy and fill it with wood, and re-drill a hole up higher, to raise the center of the rail. I'm not sure it will be enough, but it seems possible. Will keep you updated...
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Wait before you jump into changing the position of the letoff rail. This should never need to be done unless you are drastically redesigning.
If Spurlock's guide checks out on your action and the bore is correct (namely, vertical offset of the hammer assembly above the shank line), then check the knuckles. This hasn't been mentioned, but all knuckles get compressed and have roughly a 7:1 impact on hammer height for a given jack toe position. One pass of bolstering material can raise the hammer line by 1/4" or more, depending on the thickness of yarn used.
Bolster or replace the knuckles properly and this won't be an issue. If there's more than 1/4" gap at max letoff with proper bore, then you'll have to raise the rail.
Edit: Sorry, didn't read your line there at the end about the brackets and center letoff being lower than the extremities. Sounds like you have a loose/warped rail to begin with.
Last edited by Tunewerk; 05/28/15 05:47 PM.
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