Roller Size, again

[Overs Pianos]

Jon Page, Jim Bryant and list,

Sorry for the delay in getting back to this thread. Aren't weekends 
great for catching up on what we miss during work week.

Below are a couple of quotes from Jon Page.

>  I don't recall anyone saying that "a smaller roller will have
>a lower friction". Can you remember the context in which it was said?, or who
>said it?

I wrote it Jon. I was referring to the use of smaller rollers on 
those modern grand actions with a 99 mm distance between the wippen 
and jack centres (which covers most modern actions - certainly 
everything modern from Renner, Boston, Kawai, Samick, Steinway, 
Yamaha and Young Chang).

When these actions are fitted with a typical  10.5 mm roller, the 
contact between the jack and the roller will be 7 - 8 mm below the 
line of centres, ie.  between the wippen and hammer centres when the 
key is at rest. This offset makes a significant contribution towards 
friction losses in the above mentioned modern actions. If you were to 
fit a 9 mm roller in place of the 10.5, the contact point would be 
moved closer towards the line of centres. This will reduce the 
rubbing between the jack and the roller during the execution of the 
keystroke, thereby reducing friction losses. When we modify Kawai KG 
actions, which in their standard form play with a similar degree of 
difficulty to that of driving a tractor, we always fit a set of 9 mm 
diameter rollers (Abel make very nice 8 mm sets). This modification 
must usually be accompanied by a relocation of the wippen heel 
position and it's depth. Kawai KG actions have a leverage ratio which 
is generally 6:1. We change this to 5.5:1 (by repositioning the 
wippen heel and capstan). Consequently, the wippen heel will need to 
be increased in depth by about 2 mm (each action must be individually 
checked) to allow the capstan to be reset at a lower position to 
optimise the capstan/wippen heel contact.

While I realise that I have referred to three action modifications, 
and all three contribute to lowering friction losses, just using 
smaller rollers alone will reduce friction. For some pianos eg. Kawai 
GS80 The capstan position is often a little lower than ideal, yet the 
hammer/key leverage ratio is OK at around 5.6:1. The use of a 9 mm 
roller, in this instance, can be used to good effect since it will 
also cause the capstan/heel contact to move closer to the line of 
centres. In this case, a smaller roller can be used without making 
any other action changes. Some Hamburg Steinway Ds can be modified 
similarly. When we alter any modern 99 mm wippen action, we expect to 
get an upweight of 28 - 30 g with a downweight of 50 g (with centre 
pin bushing torque set at 4-5 gram/cm).

Jon (again) wrote:

>All this discussion on knuckle size prompted me to scrutinize a new set of
>shanks.
>2 sets actually. The discrepancy in height is surprising.
>
>One set ranged from .632 to .660 with the majority in the .640 to .650 range.
>The other set ranged from .610 to .640 with the majority in the .615 to
.625 range.

The variation in the mounted height of the roller from the lower edge 
of the hammer shank will have an effect similar to that of using 
rollers of varying diameter. Both hammer/key ratio and lost friction 
will vary if the roller height is not uniform. In fact when we 
replace rollers, we check the mounted height of each prior to gluing 
it in place, sanding the roller wood when necessary to a ensure a 
uniform height. Furthermore, it is important to ensure that the 
roller is fitted with the roller wood perpendicular to the hammer 
shank, since variations in the distance of the rollers from the 
hammer centres will cause significant variation in the hammer/key 
leverage ratio from note to note.

THE NEW OVERS GRAND PIANO ACTION

For those on the list who may be interested, our new grand piano 
action (patent pending) can be viewed (at rest and at check) at :

www.overspianos.com.au/actn.jpeg

We are planning to take a 225 mm grand with this action to the next 
PTG convention in Reno, July 2001. I look forward to meeting many of 
you there.

Regards to all,

Ron Overs