Hammer angle to Strings on Over Strung Upright

In my 1956 Brock, which has a HerrBergerBrooks action, I see that the base hammers are angled at about fourteen degrees to the left so as to make better contact with the wound base strings which are angle at about thirty four degrees.
From a sketch I have made it looks as if the the hammers could be set at the same angle as the strings and not touch each other.
Can somebody tell me why the hammer and string angles are not identical??

Sometimes hammer sets were not wide enough to cover bi-chords if they were set parallel to the strings.

Also, if the angle is the same as the strings, the hammers will interfere with each other when they move. Usually there is very little clearance between the top of the hammer that is moving and the tip of the adjacent, stationary hammer, even if there seems to be plenty of room when they are both stationary.

Setting a hammer parallel to the two strings in a bass unison would allow the hammer to span the maximum distance possible with it's width. Basic geometry - the shortest distance between two parallel lines is the perpendicular.

Of course there would be passing problems with hammers at 30 degrees,as BDB stated.

Picture two strings with typical 6 to 7 mm side-to-side spacing. Along the horizontal strikeline this spacing will be somewhat greater; depending on the string angle it can be as much as 8+ mm.

A typical upright bass hammer is going to be somewhere around 10.5 to 11 mm wide. If the hammers are aligned exactly in line with the strings this is more than enough width for the hammers to strike both strings precisely. But because of their length, width and bore angles they would not clear each other and it would be impossible to play the piano. At least through the bass section.

Based on side-to-side clearance requirement it would be best to install them in line with the hammershanks. Side-to-side clearance through their arc of travel would then be no problem at all. Unfortunately, because of their rounded strike face and their width the hammers will now also impact the adjacent strings of the unisons immediately below and above the note being played.

(A few years ago I wrote a couple of articles for the Journal on the design of small pianos illustrating this point.)

The ideal hammer bore angle, then, is always a compromise between side-to-side clearance through the arc of travel and not hitting the adjacent strings of the unisons above and below the note being played.

ddf

I have seen and heard hammers which have worn enough in the bass that they will hit a string on the adjacent note when they are played. Filing the hammers takes care of that, but it is one of the many problems that you can have with worn-out hammers.

That one of the problems with older hammer sets along with older sets I have come across in mostly European instruments that were not even 10mm wide.

TYpical European hammers are 2 differnt sizes as 9.5 mm and 10 or 10.5 mm

SOme can even have 3 differnt thicknesses and I have seen Grotrian or Sauter (I dont recall exactly) vertical hammers having aprogressive lenght from mediums to treble (no way to find similar hammers today, the originals where from the 80's)

At least some hammermakers will do this on request.

When we were building our 122 cm upright Abel supplied us with bass hammers that were 11.0 mm wide; tenor hammers that were 10.0 mm wide and treble hammers that were 9.0 mm wide. It is up to the pianomaker to specify these dimensions.

As well, we are able to order upright hammers of different widths from aftermarket hammermakers such as Ronsen. I don't think they even charge extra for the service.

I always order grand hammers a bit on the wide side and run them all through a jig I use on my table saw to taper them and trim them to the width I want.

ddf

I just returned from tuning some no name European upright and the hammer set was really slim; molding was 9mm, hammer felt 8mm in the bass. In the tenor/treble side the hammers were wider, 9-10mm.

Should have taken a couple of photos. I have run across some early English uprights with the same slim hammers…the names Danemann and Sames come to mind.

Renner told me that they provide grand hammers of the same width bass and treble for the US market (at last they are simpler to bore).

Basses hammer are often (not always) thinner, probably for weight questions on our grand pianos.

FOr sure if one want to repair old (and less old) pianos, a good setup to taper precisely the heads is really important, when we work on old pianos that have high action ratio even the light models from the usual suppliers can be too heavy.

I finally appreciated the trapezoid shape of the US Steinways, less easy to travel the heads but the gain in weight is huge, that goes with the style of tone on those pianos when the action is faster than today.

Most hammermakers supply after-market hammers cut to the same width. As you say, they are easier to bore. But, in the U.S. at least, most of the better rebuilders do taper them prior to installation. Generally the crown of the hammer is somewhere between 10.0 and 11.0 mm (depending on the piano) and the tail of the hammer is somewhere between 7.0 and 8.0 mm. The exact dimensions varies with the individual rebuilder.





I don't know about others but I generally cut bass hammers about 1.0 mm narrower than the adjacent tenor hammers. With a bit of fine-tuning it is possible to blend the mass of the hammers uniformly across the bass-to-tenor transition.




I don't understand this statement. One of the reasons that Steinway (and many rebuilders) cut grand hammers to a trapezoid shape is to reduce their mass. The mass of the hammers after being cut to the trapezoid shape is less, not more, than it was before being cut.

ddf

Yes Del, I noticed the mass reduction is way better when tapering the whole hammer than when tapering only the tail (or a little above the tail as it is generally done on most European grands)

I only have seen trapezoidal hammers on NY Steinways, do you mean most US grands have the same tapering done ?

My English.. "the gain in weight" reduction, of course ...

BTW, which is your preferred method to produce a full tapering on hammers ? I use the nice Spurlock gig, but mosty often it is only to taper the tails (up to the agrafe) so I do that on a large sandiong disk (grit 150)

Above, the felt get dirty easily. Tapering with the precision circular saw table is excellent but a little longer, and it is very difficult to keep the good parallel position with the smaller hammers (that said even on factory done job, I often noticed the high treble hammers look like if they have been bored in the same orientation than the basses ( at 2-3 ° ) as it is not something that correspond to the strings orientation, I was suspecting loss of squareness during the tapering (but also, why not, at the moment the hammers where sliced, due to the slant of the felt for instance...)

I also have wandered for some time if a non square to strike line shape (for treble hammers) was not a way to "open" the tone (as Bluethner with their particular slicing, that provide a really special tone)..

Trying to have non identical spectrum for any of the 3 strings of the unison is a way top en-light the tone...

Regards

Many did, but not all. It is now common among better piano rebuilders.




Ah, I understand.




I use a jig -- actually a pair of them; one for the first side, another for the second side -- of my own design. They use "toggle clamps" to hold the hammers in place and I am able to do all 88 of them. I start the cut right at the top of the hammers and cut all the way down. If I am reducing the overall width of the hammers I set the two jigs up so an equal amount of material is cut from each side. (Important since they have already been bored....)





Perhaps. I'm not aware of any U.S. manufacturers who did that. Steinway -- and the several manufacturers that made careers of copying them -- did make the strings of the lower treble section of unequal length (by staggering the bridge pins) for a while. But this had more to do with trying to overcome a soundboard design problem than anything else.

ddf

For what I have seen, Bechstein also have clearly different lenghts in the top sections (and why not, may be lower too)

Your gigs use a saw or sanding disks ?

I have seen a neat setup with a large cutting disk, (horizontaI , could be used to slice bass hammer sides tool) I thought I could buy an old ham slicing machine and modify it. I understand that 2 setups is way more efficient ..

Best...

Circular saw.

The last time I tapered a set of hammers I started dreaming of a safer system using a large, slow turning disc sander. I have the hammer holding devices designed in my head and I may just switch.

ddf

One of the many things that make a ShopSmith worth having for piano work. Nothing like a sanding disc on a quill.

Del:

In the PTG article did you cover what happens when the shank is set at an angle to the vertical? The hammer then travels in a cone instead of a plane. And for the hammer to be perpendicular to the strings when striking them, they cannot be perpendicular to the strings when at rest.

When I replaced the hammers on my own Walter Console, mostly as a project, I ran into this and decided the improvement in tone was worth it. But my, oh my, did I have to do some tapering for clearance! I did cheat on the lowest bass notes, though. They don't hit the strings quite perpendicular, but I don't think it is as important with single strings. The tone improvement is probably from the better hammer mating.

No, I did not. I don’t know of any modern pianomaker doing this. Probably for good reason. Unless the hammerbutt flanges were also angled—A nightmare I don’t even want to begin contemplating!—I should think it would increase the torsional stress on the hammershanks (introducing a lot of erratic hammer wobble) and the hammerbutt flanges introducing increased action center wear. But I must admit I haven’t really thought about this much. (Question: Without altering action center spacing on the action rails how much can you angle those hammershanks?)

The articles came about, in part, because I regularly hear from people who tell me that “good pianos” have a lot of—or very little of—this or that particular feature. Usually it is something like string length (especially in the low bass of very short pianos), string angles (again usually, but not always, in short pianos), scale tensions, soundboard area or some such. According to these claims it should be possible to come up with concert grand performance in a piano the size of a spinet. If only I would do such and such….

Briefly; as they might apply to this topic:

From a purely theoretical standpoint when laying out an overstrung scale to fit in a short piano it would seem that the more we angle the bass strings the better. Why not, after all, take full advantage of one of the only two inherent benefits of overstringing and make those bass strings as long as possible? As you discovered with your Walter, though, there are downsides to this approach that may not, at first thought, be apparent.

Side-to-side string spacing within the bi-chord unisons is a more-or-less fixed dimension. Typically bi-chord agrafe hole spacing is 6 mm. Even if we don’t use agrafes we still have to stay close to this spacing. Side-to-side bridgepin spacing varies but it is usually around 7 to 10 mm. No matter the string angles we cannot decrease either of these by much or the strings are going to start hitting each other; especially as the overall diameter of the strings increases (which it does quickly in short scales).

With the strings at 90° to the strikeline side-to-side spacing between the notes—the action center spacing—could safely be as little as 13 mm (plus or minus some small amount) without causing any string clearance problems between notes. As the string angles increase, however, the action center spacing must be made increasing greater to keep the strings from adjacent notes from hitting each other. This is not a big deal until the string angles are made greater than about 30° – 35°. Action center spacing of around 14 mm will suffice; not a big increase. Much beyond this and the action center spacing has to be increasingly wider and once you pass 40° action center spacing has to be made increasingly wider by a lot.

Making the action center spacing wider, of course, makes the piano wider and it increases the amount of keyflare required. Increasing the keyflare increases the amount of side force on the keybushings causing them to wear out faster. It also results in an increasing amount of twist to the key and this increases action saturation.

If we’re going to attempt to align the hammers with these steeply angled strings there are also going to be problems. We’re going to have serious side-to-side clearance problems through the hammer’s arc of travel. Here we have two possible solutions: we can make the hammers thinner—the opposite of what we want in the bass section for acoustic performance—or we can increase action center spacing. Once the boring angles go much beyond 15° – 18° or so clearance through the hammer’s stroke becomes a problem. (Anyone doubting this has never replaced a set of hammers on a square!) So, we either limit our bore angles or, again, we have to increase the action center spacing beyond reasonable limits.

If we limit our bore angles and don’t align the hammers to the strings then once again action center spacing will have to be increased or the hammers will begin striking the neighboring strings of the adjacent unisons.

Etc. (Does anybody notice a trend here?)

The point of the article was that it is easy to focus on one or two scale or design parameters and say that this or that should be done to make a good piano. The reality is somewhat more difficult; choices must be made and compromises must be found. The best pianos will be those in which the designer has made reasonable and artful choices that result in a suitable balance between all of these.

ddf

Thats interesting..

What about the mass distribution on the shank>flange, with those tweaked setups we find in many grand pianos ? (strong papering vs shank burning)

On smaller pianos the shanks can even be positionned far left or right of 90° from the rail, it allow to lower the amount of papering and shank burning.

I thought that, due to the hammer angle, ther was a relatiovely large mass differnce between both sides of the sHank.
There is a differnce indeed (the center of equilibrium is not on the center of the shank) .
But this is relatively small and only exacerbated during the motion (due to the flex of the shank possibly)

At some point at rest the angle allows the hammer mass to be centered.

The papering, not only will only allow the hammer to travel to the strings without touching the neighboors, but it helps to even the pressure on the center, anyway to some point.

I have seen differnt setups in regard of the vertical

hammer vertical : square to the strings ; no mention of the hammer thicker on the left but this can be in the same direction than the slant the 3 strings adopt sometime

on pianos with "combs" (one center = 20 flanges) the hammers at rest are a lot angled, an they get back to vertical at contact moment (PLEYEL°

On some gands with large angle I have seen the vertical attained at half stroke.
On many grands however, the hammer looks vertical at rest but it is papered a lot.

On some pianos, the traveling is good when the spaces are even between top right and back left of the head, but on some others the tail have to be bertical , centered between the 2 adjacent hammers when the head is at string level..

I have seen sketches showing the gravity center displacment during the hammer travel, but I never find one explaing the gravity motion in the lateral plane.

If any study have been done on the subject I would be very interested to read it...

Best regards

To find the gravity center of a grand hammer you lay it on a blade on the shank, then on the head.

the gravity center is at the intersection of both dots projections.

correct ?

That method can be used (or on a needle) to find the gravity center of angled hammers, it allows to see where is the mass deported. (angle of the head vs the vertical)

the point move depending of the inclination of the shank.

That gravity center displacmenet is very probably what the regulation allow to feel under the finger.

Thanks for all the interesting disscussion. I'm tempted to buy a digital piano so that I can play whist I experiment with my upright.
May be take off the first three hammers in the base so that I can tinker with the first two !
I was thinking that to repair badly worn hammers, after shaping back to a reasonable profile, one could use 10mm Kevlar woven tape?
Glue it to the wood of the hammer and strech it round re reshaped profile.