Pianotech

.5 mm more realistic. Need to allow for wood movement.  Main purpose of dag is to secure key frame during transport.

I was under the impression that the ONLY reason for these restraints was for moving purposes. Same as for the "key up-stop rail", and the L shaped thing-a-ma-gig under the trap work. 

Peter Grey Piano Doctor 

I don't remember which 'old' Steinway tech explained this to me (and some other - less old) Steinway tech may disagree, but the positive 'capture' of the back rail serves to stabilize the action bedding to, among other things, prevent a 'knock' that can be mistaken for balance rail knock (but it's the back), a well as allowing the  glides some positive pressure putting some flex into the frame, making it effectively more rigid.
My hallucination-prone memory also recalls somewhere in Steinway's video-training materials referring to the glide bolts as suitable for slight key-height adjustment which, if true, would definitely require positive pressure on the back rail.  That's a BIG IF.

The dag/dogs (but not Tags) should not be used to compensate for sloppy rail bedding.

The official name for the Steinway part is "keyframe hold down dag block". That's a mouthful so we simply call them "dags". (You'll never hear someone from Steinway call them dogs which implies a holdfast. An action with an una corda function should never be held fast)

The dags are supposed to touch the keyframe by design, but as lightly as possible to allow for the action to shift. Turning the glides way up and inserting something like a .005" shim to test contact would be appropriate. 

Steinway does not recommend or condone the practice of using the "balance rail stud" or "glide" to adjust the key height / key dip, regardless of the fact that the legacy name for this part is  "TR screw" (touch regulating).

Can the balance rail stud be used to cheat and effectively increase or decrease aftertouch? Yes it can, but unless there is a really good reason to do so, Steinway doesn't recommend it. 

I don't remember which 'old' Steinway tech explained this to me (and some other - less old) Steinway tech may disagree, but the positive 'capture' of the back rail serves to stabilize the action bedding to, among other things, prevent a 'knock' that can be mistaken for balance rail knock (but it's the back), a well as allowing the  glides some positive pressure putting some flex into the frame, making it effectively more rigid.
My hallucination-prone memory also recalls somewhere in Steinway's video-training materials referring to the glide bolts as suitable for slight key-height adjustment which, if true, would definitely require positive pressure on the back rail.  That's a BIG IF.

The dag/dogs (but not Tags) should not be used to compensate for sloppy rail bedding.

The official name for the Steinway part is "keyframe hold down dag block". That's a mouthful so we simply call them "dags". (You'll never hear someone from Steinway call them dogs which implies a holdfast. An action with an una corda function should never be held fast)

The dags are supposed to touch the keyframe by design, but as lightly as possible to allow for the action to shift. Turning the glides way up and inserting something like a .005" shim to test contact would be appropriate. 

Steinway does not recommend or condone the practice of using the "balance rail stud" or "glide" to adjust the key height / key dip, regardless of the fact that the legacy name for this part is  "TR screw" (touch regulating).

Can the balance rail stud be used to cheat and effectively increase or decrease aftertouch? Yes it can, but unless there is a really good reason to do so, Steinway doesn't recommend it. 

I don't remember which 'old' Steinway tech explained this to me (and some other - less old) Steinway tech may disagree, but the positive 'capture' of the back rail serves to stabilize the action bedding to, among other things, prevent a 'knock' that can be mistaken for balance rail knock (but it's the back), a well as allowing the  glides some positive pressure putting some flex into the frame, making it effectively more rigid.
My hallucination-prone memory also recalls somewhere in Steinway's video-training materials referring to the glide bolts as suitable for slight key-height adjustment which, if true, would definitely require positive pressure on the back rail.  That's a BIG IF.

The dag/dogs (but not Tags) should not be used to compensate for sloppy rail bedding.

I don't remember which 'old' Steinway tech explained this to me (and some other - less old) Steinway tech may disagree, but the positive 'capture' of the back rail serves to stabilize the action bedding to, among other things, prevent a 'knock' that can be mistaken for balance rail knock (but it's the back), a well as allowing the  glides some positive pressure putting some flex into the frame, making it effectively more rigid.
My hallucination-prone memory also recalls somewhere in Steinway's video-training materials referring to the glide bolts as suitable for slight key-height adjustment which, if true, would definitely require positive pressure on the back rail.  That's a BIG IF.

The dag/dogs (but not Tags) should not be used to compensate for sloppy rail bedding.

Interesting.  That would explain the rounded portion of the dag, to reduce contact area.  I suppose that would need slight taper/wedge shape as well, to guide it home?

Still, seems dangerous to have moving parts that actually touch like that, especially since there is so much friction between the keyframe and key bed already.

------------------------------
Tom Dowell
Hulbert Piano
tom@hulbertpiano.com
262-221-0792
------------------------------


Original Message:
Sent: 05-23-2026 11:59
From: Peter Acronico
Subject: Dag/Dog pressure or clearance Spec?

Why is contact at this point any more dangerous than the contact (and its friction) along the entire keyframe/keybed?  or keyblock plate and end pins?  And, for that matter, why dangerous?  It's just one more thing we have to learn to do carefully.

Interesting.  That would explain the rounded portion of the dag, to reduce contact area.  I suppose that would need slight taper/wedge shape as well, to guide it home?

Still, seems dangerous to have moving parts that actually touch like that, especially since there is so much friction between the keyframe and key bed already.

------------------------------
Tom Dowell
Hulbert Piano
tom@hulbertpiano.com
262-221-0792


Original Message:
Sent: 05-23-2026 11:59
From: Peter Acronico
Subject: Dag/Dog pressure or clearance Spec?

Well, if a piano gets mad, it can quickly turn on you and attack, and this becomes more likely the deeper in the action cavity you are working.

Seriously, though, this is dangerous in the sense that it can create a difficult to diagnose, major problem. In this case, because the wood would be contacted on both sides, it could become clamped, making the una corda pedal not work, or even locking the action in the action cavity. 

Danger is always relative.  I don't think anyone's health is in danger, but possibly my reputation!

Why is contact at this point any more dangerous than the contact (and its friction) along the entire keyframe/keybed?  or keyblock plate and end pins?  And, for that matter, why dangerous?  It's just one more thing we have to learn to do carefully.

Interesting.  That would explain the rounded portion of the dag, to reduce contact area.  I suppose that would need slight taper/wedge shape as well, to guide it home?

Still, seems dangerous to have moving parts that actually touch like that, especially since there is so much friction between the keyframe and key bed already.

------------------------------
Tom Dowell
Hulbert Piano
tom@hulbertpiano.com
262-221-0792


Original Message:
Sent: 05-23-2026 11:59
From: Peter Acronico
Subject: Dag/Dog pressure or clearance Spec?

I like the term dangerous here as it seems that this is a difficult feature to measure and adjust and it could potentially be a source of a hard-to-find problem, like a knock, squeak or loss of power.  Removing a front rail knock by sanding away all places where no knocking occurs is hard enough.  Try doing this to a back rail, where even diagnosing it is difficult.  How often do we insert a thin dowel through the strings to contact the back rail and check for bedding?

Well, if a piano gets mad, it can quickly turn on you and attack, and this becomes more likely the deeper in the action cavity you are working.

Seriously, though, this is dangerous in the sense that it can create a difficult to diagnose, major problem. In this case, because the wood would be contacted on both sides, it could become clamped, making the una corda pedal not work, or even locking the action in the action cavity. 

Danger is always relative.  I don't think anyone's health is in danger, but possibly my reputation!

Why is contact at this point any more dangerous than the contact (and its friction) along the entire keyframe/keybed?  or keyblock plate and end pins?  And, for that matter, why dangerous?  It's just one more thing we have to learn to do carefully.

Interesting.  That would explain the rounded portion of the dag, to reduce contact area.  I suppose that would need slight taper/wedge shape as well, to guide it home?

Still, seems dangerous to have moving parts that actually touch like that, especially since there is so much friction between the keyframe and key bed already.

------------------------------
Tom Dowell
Hulbert Piano
tom@hulbertpiano.com
262-221-0792


Original Message:
Sent: 05-23-2026 11:59
From: Peter Acronico
Subject: Dag/Dog pressure or clearance Spec?

Blaine Hebert's post rescued me from the mire I had submerged into trying to respond to Daniel D's excellent response.  He brings us 'full-circle' with "How often do we insert a thin dowel through the strings to contact the back rail and check for bedding?"  Well, my response is "Only when necessary",  though, as with string-splicing, we should perhaps be doing it more frequently, just to develop or maintain our skills (and our positive attitude).  But it cleverly brings us back to our original author - Tom Dowell - whose question was about the intended parameters of the dag/dogs when doing the initial set-up, not analyzing or correcting a problem in the field.  This is about proper keyframe fitting, which is accomplished (initially) with keyframe only.  Whatever distortions are later introduced by the weight of the keys and action frame, or twisting introduced by careless cleat (? - under feet of action frame) preparation will not alter the one to one relationship between the thickness of the back rail and the height to the underside of the dag/dogs.  
A secondary note:  the 'thin dowel' only helps in locating an ambiguously-sourced 'knock', not a binding dag/dog.  I have a 'first-line' method for assessing the loose fit which I'll describe in response to Daniel's post, to give him first dibs at shooting it down.  Rudimentary testing for excessive tightness can be observed by noting any significant difference in una corda resistance as action is being inserted or removed from cavity. 

This is just an annoyance.  AND,  it's probably one of the last of our skills that AI will replace.

Save DANGER for things like actually arriving safely to a job, or going out without your passport, or war. 

Honor Memorial Day, by thinking about it, or going out to by a washing machine.  That's what we do. 

I like the term dangerous here as it seems that this is a difficult feature to measure and adjust and it could potentially be a source of a hard-to-find problem, like a knock, squeak or loss of power.  Removing a front rail knock by sanding away all places where no knocking occurs is hard enough.  Try doing this to a back rail, where even diagnosing it is difficult.  How often do we insert a thin dowel through the strings to contact the back rail and check for bedding?

Well, if a piano gets mad, it can quickly turn on you and attack, and this becomes more likely the deeper in the action cavity you are working.

Seriously, though, this is dangerous in the sense that it can create a difficult to diagnose, major problem. In this case, because the wood would be contacted on both sides, it could become clamped, making the una corda pedal not work, or even locking the action in the action cavity. 

Danger is always relative.  I don't think anyone's health is in danger, but possibly my reputation!

Why is contact at this point any more dangerous than the contact (and its friction) along the entire keyframe/keybed?  or keyblock plate and end pins?  And, for that matter, why dangerous?  It's just one more thing we have to learn to do carefully.

Interesting.  That would explain the rounded portion of the dag, to reduce contact area.  I suppose that would need slight taper/wedge shape as well, to guide it home?

Still, seems dangerous to have moving parts that actually touch like that, especially since there is so much friction between the keyframe and key bed already.

------------------------------
Tom Dowell
Hulbert Piano
tom@hulbertpiano.com
262-221-0792


Original Message:
Sent: 05-23-2026 11:59
From: Peter Acronico
Subject: Dag/Dog pressure or clearance Spec?