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Joined: May 2012
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Hello,

Maybe someone can help here... There is a school whose pianos I service. They have a 90 year old Bradbury 6' grand. It is a bit of a frankenstein from previous technicians' work... nevertheless, not a bad instrument.

I was pointed to a few notes that do not work when played fortissimo. So, of course, it is the backchecks are very steep and getting caught on the hammer tails. Also, the checks are a bit worn (but not too bad).

In any case, for over half the piano, it seems that I cannot get the checks in such a place that I get clearance and good checking. Either no checking (which is where about half the piano mostly was when I found it) or it checks but it has friction or is getting caught with a hard blow.

I've been futzing with it all evening and it just seems that the tails are improperly arched... Even adjusting the angles more vertical on backchecks seems to get clearance sometimes, but the tails hit so high on the check that they bounce on the top of the check after hitting the string. Or... If I make the check less vertical, I can get decent checking, but the tail is catching the bottom of the backcheck on the way up during hard strikes.

I cannot get it to work just right... It is either one problem or the other. I think another technician was dealing with the same thing (or he/she created the problem) because less than 20% of the notes properly check on the instrument. All are either dragging or just not close enough to check or interfere .

You get my point. So... any help?

Thanks!

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Very difficult to say without seeing the action, but it sounds like the checks might be a bit too tall. If they’re the screw on head type, you could try winding a head down a couple of turns to see if that helps. On my current rebuild, the checks were 7mm too tall, and the hammers were resting on them in the bass and tenor; I ended up knocking the checks 7mm further into the keys which sorted out the problem. I’ve added #checkalteration to an Instagram post that shows the procedure smile


Started work at the Blüthner piano re-building workshop in Perivale, UK, in 1989. Self employed since 2000. Learning something new about pianos every day... smile

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I worked on one once where the repetition springs were too weak to lift the hammer out of check and they were hanging up. A tech before I got there had moved them too far back to where they would barely check at all. But it solved the hanging up. I was able to strengthen the springs enough to help. It was definitely a frustration in geometry. I like to catch the tails midway in the arc when possible.


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Wild guess:

The piano at one point has got a new set of hammers and the shape of the hammer tails is different from the original ones. The only remedy known to me: New backchecks that fit the new hammers.

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Fundamentals first. This being a school piano, neglect of basic things like periodic action regulation is a likely culprit. Are the hammers sitting on the rest rails? Does a straight edge on top of the keys show a trough in the middle of the piano? How much aftertouch is there in the offending notes (if any)?

Here is your check for backcheck height: Regulate a few notes to where they are letting off at about 1/8" from the string. Place the action on the bench with the hammer side facing you, slowly depress the key and watch the hammer cycle through let-off and drop. At let off, the bottom of the tail should be about 1/16 of an inch above the top of the back check. Check this in several places in the scale.

If you do not have enough aftertouch when you do this, remove enough punchings from the front rail so that it will cycle through let off and allow your test.

If the rep springs are weak, you can do this test at the same bench time. Hit a key, the hammer travels up and down and is caught by the backcheck. Slowly release the key to allow it to rise. At a minimum, you should be able to see the hammer rise up a ways. This would show that the spring is sufficiently strong to lift the hammer and allow the jack to reset under the knuckle, thus allowing repetition.

Do these tests before you start changing back check heights. Otherwise, you are putting the cart before the horse.

When we depress the key in the front, the backcheck at the other end is traveling in an arc upward and inward. If you lack sufficient travel in the key (due to settling), then the key travels less distance than it would when regulated well. The cycle is over before the backcheck has the opportunity to travel far enough inward to engage the hammer tail.

Because backchecking is dependent on a number of other adjustments being in their proper place, adjusting the back checks is on the the last things I do in action regulation.


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Adding to Williams excellent suggestions, too worn back checks can cause the symptoms you describe. Try bolstering one of the back checks by inserting cloth under the leather and see if that helps. Also make sure the hammer tails are not glazed. They don't need to be really rough, but they do need some.

Beyond all of this it is a 90 year old piano and is past its serviceable life.


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Thank you everyone. I'll definitely check it out on Friday (pun somewhat intended...). The action regulation is well... functional. Springs are fine, key height is correct, blow distance was low but I didn't think that was getting in the way. However, the let-off does need correction, on some keys it is a mile away, on others it is okay. That is obviously messing with the aftertouch.

All that being said, the hammers are older than the backchecks. This was one of the school board members pianos and it was donated. Soundboard is nice and although 90 years, it was rebuilt likely 40 years ago by my estimate.

I now teach piano at the school so they've brought me on as a technician too... The school said they used a number of technicians who all spent minimal time there. They were surprised at my first tunings taking 90 minutes and sounding so good! They said the previous tuners took 30 minutes per piano....

In anycase, I'll key you updated. I haven't posted here in about 4 years and it is great to get such a vibrant and helpful response! It made me happy with humanity to have this board today.

Cheers!

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In addition to what has already been suggested, one "routine checking maintenance item" to look into is to slightly roughen the tails when checking is "iffy". I just use my sandstick and rub it lightly cross-grain (treble-to-bass) in the area where the tail contacts the check. Many times... problem gone.


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PianoIndy, when you try to adjust the backchecks, are you just bending them forward and backward, or are you also trying to adjust the angle of the head? Your mention of the hammers sometimes just bouncing off, instead of checking, makes me ask. Sometimes there is a "sweet spot" of angle and of distance where they work best. Also, rather than testing with a hard blow, you can pull the backchecks toward the front of the piano and see if the hammer will clear when pressing a key. And also with the action out of the piano, you can let the hammer drop from about 60 degrees with the key depressed to see if they will check.

As was mentioned, roughing the hammer tail with sandpaper is good. So might be scuffing the backcheck with a small wire brush.

Sorry if this is already what you are doing. But be sure to let us all know what works. smile


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Hello all,

Mostly working now. Because I was called in and directed towards the problem, I was hoping I could fix it without a full regulation. In any case, I did reset the hammer line, let-off, drop, after touch and even went over the key level before doing all this. Most of the checking came after this. I did have to adjust the angles which I was already doing on some. Before the original post, I had already wire brushed the checks (which seemed glazed) and scuffed the tails with 60 grit sand paper. On the work bench, all the checks were good. In the piano, I had a few that still wouldn't check when I returned the action. So, I'll investigate when I have more time on Monday. As I mentioned, I teach here now (now mostly online) and they've given me a good bit of time to rehab a number of their pianos. So now, the action is functional, but gotta do a little more fine tuning of the regulation....

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Final update. As William pointed out, fundamentals first... The back checks can only work when all the other regulation is in order. Indeed, once regulated, most of the checking issues cleared up. There was a little bit of scuffing and de-glazing of the tails to be done. Also, some checks did have to have their angles adjusted and the position adjusted. Essentially, as we all know, most parts of regulation effect most other parts of regulation. So, it is hard to look at any problem in isolation. Lesson learned .. rather re-learned which is a good thing to keep front of mind. Thanks all


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