DESIGN OF THE OVERS ACTION

A class presented at the Reno 2001 PTG convention by Ron Overs
11-15 July, 2001

INTRODUCTION

Ron Overs has had a 27 year history of service dedicated to the Australian piano industry. His rebuilt grand pianos - recently incorporating more and more of his own design changes - can be found in many of Australia's concert and recording venues and institutions. He has come to be recognised as Australia's premier grand piano rebuilder. Ron's passion is design.

Over the past eighteen months, Ron has undertaken the development of his first production grand piano. The Overs-Steinbach 7'4" grand piano is the culmination of years of prototyping on the pianos of other manufacturers. Coming to piano manufacture as a tuner/technician, Ron was determined to tackle problems such as tuning stability and inefficiencies of design head on, when building his own piano. He started with scale design and is presently focussed on the piano action.

In December 1998, while surveying the available contemporary grand piano action designs for use in his own grand piano, Ron concluded that none had the leverage systems optimised to reduce friction to a practical minimum. The first half of 1999 was dedicated to modifying an existing action to research the feasibility of a new improved design. In August 1999 he commenced work on a new design. Much CAD development was undertaken and by December several possibilities had been narrowed down to a preferred option. A test model was built in January 2000. The preferred model proved to be very close to the final working prototype, which was completed in February 2000.

The modern grand piano action, originally conceived and designed by Sebastian Erard in the early 1800s, has once again has been the subject of the evolutionary process. The Overs action is proving to be a significant step forward in grand piano action performance.

An Overview of the Action Design Improvements

In this grand piano action redesign, every lever and its relationship to its opposing member or contact surface has been examined and revised to minimise friction and to improve control and response time. To achieve this outcome, the following principal features of the design were modified;


Three dimensions of the action were revised to reposition the jack/knuckle contact, allowing it to move through the line of centres at the half blow point. These were:


(i) The knuckle slot to hammer flange centre distance was increased from the contemporary standard of 17.00 mm to 20.0 mm.

(ii) The wippen flange centre to jack centre distance was reduced from the contemporary standard of 99 mm to 75 mm.

(iii) The knuckle (roller) diameter was reduced to 9 mm diameter.

The repetition-lever-centre position was altered to minimise friction between the repetition lever and the knuckle.

A new screw adjustable repetition lever/jack spring was designed to reduce friction between the spring arms and the repetition lever and jack.

The drop screw was relocated to the hammer side of the hammer flange centre.

A new jack tender (tail) was designed to achieve a specific relationship between the tender angle and the radius of the tender/letoff button contact arc, to minimise friction and wear.

Other features of this design, which have been used on previous piano action designs include;


A repetition lever flange design was chosen which performs the functions of;


(i) repetition lever flange

(ii) jack position stop

(iii) mount for the repetition lever height/position adjusting screw.

(iv) Repetition lever over-travel stop

A screw adjustable wippen helper spring.

Hammer stop rail adjusted to meet the hammer shank


DETAILS OF THE OVERS ACTION DESIGN

1) Jack/knuckle contact point re-positioned

In other contemporary action designs, when the hammer is at rest the jack/knuckle contact point is typically 7 to 8 mm below the line-of-centres (ie. the line between the wippen flange and hammer flange centres), whereas at let-off the jack/knuckle contact will be 2 mm below the line-of-centres. The mean position of the jack/knuckle contact point, with respect to the line of least friction, will therefore be 4.5 - 5.0 mm distant from the line of least friction. Hence the jack/knuckle contact, in other contemporary designs, never gets closer than 2 mm from the line of centres.

In the Overs action, when the hammer is at rest, the revised jack/knuckle contact point is positioned 3.5 mm below the line-of-centres, moving through the line of centres to 3.5 mm above the line at let-off. Therefore, the mean position of the jack/knuckle contact point is positioned directly on the line-of-centres. This geometry change in the Overs action was achieved through the combined effect of the following changes, the last of which is new;

1) The wippen flange centre to jack centre distance was reduced from a typical 99.0 mm, as found on most contemporary actions, to 75.0 mm. The reduction of the wippen length is not a new idea. A Schwander design used in a Rogers grand piano from around 1920 had a wippen with a 70 mm flange to jack centre distance. A Langer grand action from 1909 had what appears to be around 68 mm. But neither of these designs used a 9 mm knuckle (roller) positioned 20 mm out from the hammer centre.

2) The knuckle (roller) diameter was reduced from a typical 10.5 mm to 9.0 mm. In the later part of the twentieth century, action designers have tended to specify larger diameter knuckles. This has been a retrograde step with respect to action geometry and friction.

3) The knuckle slot distance from the hammer flange centre was increased from the typical 17.0 mm, of other contemporary actions, to 20.0 mm. While this new setting increases the mean rotational speed of the wippen by 7% with respect to the hammer (when compared to other contemporary actions) it reduces the pressure loading of the knuckle on the jack by a corresponding amount. This will reduce the wear and tear on the knuckle slightly, while increasing the wippen speed will increase inertia. This negative inertia effect is offset in the Overs action, since the shorter 75.0 mm wippen weighs only 18 grams, compared to 21 grams for a typical 99.0 mm wippen.

The Overs action is the first action design in which these three parameters have been used together in the one action design - part of the patent claim.

2) Repetition lever centre re-positioned

The repetition lever contacts two friction surfaces during the execution of a key stroke - the knuckle and the drop screw. Contact with the drop screw occurs at or just prior to the contact of the jack tail (tender) with the let-off button. The contact pressure between the repetition lever and the knuckle is at its most extreme when the hammer is in the check position.

An investigation of the repetition-lever-centre position, and its effect on friction between both the repetition/knuckle contact and the repetition/drop screw contact, will show that it is not possible to position the centre such that it simultaneously minimises friction between these two contact surfaces. Therefore, since repetition lever/knuckle friction has the more significant influence on the dynamic performance of an action, a decision was made to position the repetition centre to minimise repetition lever/knuckle friction as the hammer rises out of check. In other contemporary designs there is considerable fiction between the repetition lever/knuckle contact during 'hammer rise' out of check, since the repetition centre is not ideally positioned (it is usually positioned too high). In the Overs action, when the hammer is in the check position the repetition lever centre, repetition/knuckle contact and the hammer flange centre are all aligned, resulting in reduced friction between the jack and repetition lever as the hammer is released from the back-check. As an additional benefit, this geometry revision allows the repetition spring to lift the hammer out of check at a lighter spring loading. The repetition lever spring must work against friction between itself and the repetition lever, the repetition/knuckle friction and the hammer/shank weight, effectively to raise the hammer out of the check position. Since the spring arm friction and repetition lever friction is reduced, the repetition lever spring pressure required for correct action function with the heavier bass hammers can be approximately 20% lower in the Overs action.

3) A new repetition lever/jack spring design

The repetition lever/jack spring system has been completely revised in the Overs action. The repetition lever spring is new, with the spring pivot point (coil) re-located from the repetition lever flange to the underside of the repetition lever. While there are previous designs with the repetition spring mounted on the repetition lever, in the Overs action the spring has been positioned such that the lower spring arm (as it leaves the coil) is located substantially on the line of centres between the repetition lever and jack centres. While some other designs such as the modern Baldwin wippen might appear to be similar to the Overs action, the lower spring arm of the Baldwin wippen does not lie on the line of centres. Furthermore, the Baldwin repetition lever spring has a single coil positioned midway along the lower spring arm, presumably to achieve a more uniform spring rate. In the Overs action the repetition lever spring is manufactured with three and one quarter coils at the pivot point to achieve a more uniform spring pressure. The upper spring arm has been reduced to a short specially shaped tail, which sits on and is centrally located by the repetition-lever-spring adjustment screw. The adjustment screw is mounted in the repetition lever between the lever centre and the jack throat. In contemporary double wing (butterfly) spring action types, the position of both spring arms is less than ideal. Even in the Renner design with the spring tension adjusting screw, there is considerable movement between the screw and the upper spring arm. In conventional double wing spring actions, where the spring bears against a slot under the repetition lever, the movement between the spring upper arm and the repetition lever spring slot is increased further, resulting in greater friction and noise in many high use actions. Repetition lever spring-arm friction is minimised in the design of the Overs action, further reducing the repetition lever spring tension required to raise the hammer out of the check position. Furthermore, in the Overs action, the lower spring-arm hole in the jack has been re-positioned to lie substantially on the line-of-centres between the jack and repetition lever centres. This also is positioned to minimise the movement of the jack spring lower arm in the jack-hole during the let-off.

4) Drop screw re-location

As mentioned previously, the repetition lever centre was re-positioned to minimise friction between the repetition lever/knuckle contact. A negative effect of this is that it slightly increases friction between the repetition lever and the drop screw. However, since the knuckle slot was moved to 20.0 mm from the hammer flange centre in the Overs action, considerably more space was created between the knuckle and the hammer flange centre. This allowed room for both the jack throat and the drop screw to share the available space. A decision was made to move the drop screw, since relocating it to the other side of the hammer flange centre would reduce slightly the friction with the drop screw. Furthermore, it allows for a noticeable increase in the rigidity of the hammer flange, while at the same time allowing the repetition lever to be shortened and lightened. This drop screw re-location is not possible on other contemporary action designs, since the shorter distance between the hammer centre and the knuckle slot precludes it. This modification, previously thought to be unique to the Overs action, was discovered recently in an action design from the early 1930s. This particular aspect of the Overs action must therefore revert to the status of prior art.

5) A new jack tender (tail) design

The jack tender (tail) angle has been altered by positioning the top arc of the tender close to the line-of-centres between wippen flange and jack centres. The tender arc radius and position has been determined to minimise friction between the jack tender and the let-off button. During let-off, ie. from the instant the jack tender contacts with the let-off button to the check position, the jack tender arc center moves parallel to the surface of the let-off button by approximately 2.0 mm. During the course of this movement, the jack rotates through an arc of approximately 7 degrees. The magnitude of this movement will vary slightly relative to the key dip. During the let-off, the peripheral travel distance of the jack tender arc (about the jack tender arc centre), and the travel distance of the tender arc center parallel to the contact surface of the let-off button, will be within a couple of hundredths of a millimetre of each other. In the Overs action, all parameters including the angular rotation of the jack and its travel distance across the face of the let-off button were calculated using CAD analysis. This reduces friction at the let-off button/jack tender contact to a minimum, while also minimising wear of the let-off button face material. Let-off adjustment will tend to remain in correct regulation for a longer service period on an Overs action. In other contemporary actions let-off button wear, and the subsequent upward movement of the let-off position has been an ongoing problem for technicians maintaining concert instruments.

Two factors contribute to the improved let-off regulation stability of the Overs action;


a) The movement of the jack tender across the face of the let-off button will be a rolling type of movement, and not a gouging action.

b) The movement of the jack tender arc across the face of the let-off button will spread any wear and compression of the letoff button material covering over a larger surface area, thereby reducing the wear and compaction of the surface.

6) Four function repetition lever flange

A four function repetition lever flange (not part of this patent claim since it is prior art) functions as;

(i) repetition lever mounting flange

(ii) repetition lever over-travel stop

(iii) jack position stop

(iv) repetition lever height/position adjusting screw mount.

The dimensions of the block, the repetition lever and the box cloth washer underneath the repetition lever, have been deliberately chosen to allow the box cloth washer to act as a true repetition-lever-travel stop, preventing over-travel of the repetition lever during heavy playing.

7) An Adjustable Wippen Assist Spring

The wippen assist spring is located at the back of the wippen body, The active assist spring arm is connected to the wippen flange by means of a traditional loop cord. This spring assist system has been used in several previous action designs. The adjustable grub screw allows for fine regulation of the assist spring loading. Major adjustment of the assist spring loading is achieved by closing or opening the spring coil in the traditional manner. The assist spring supports part of the hammer mass and that of the wippen assembly, thereby reducing both the down weight and up weight. However, it is not practical or desirable to eliminate key leads completely (ie. not without substituting the lead weights with the MBA system), since the assist spring tension that would be required if used alone to adjust the down weight to an appropriate level, would interfere with back check operation. Therefore, best practice would be to use a combination of less key leads with the assistance of an adjustable wippen assist spring. As an added benefit, the adjustable assist spring also allows for the action balance weight to be modified to suit an individual pianist's requirements. The employment of assist springs, in combination with less key leads, allows for a faster and more responsive action with less key inertia.

For those technicians and piano manufacturers who are philosophically opposed to the idea of employing wippen assist springs, there is no reason why an Overs action could not be used (under licence of course) without the assist spring. However, it is not recommended that assist springs be employed without the adjustment screw. The author believes that assist springs have gained a controversial reputation as a consequence of inappropriate regulation in both factory and retrofit installations, which have been used without an adjustment screw.

Conclusion

The Overs action was launched at the Sydney APTTA convention in July 2000, and has been enthusiastically received by the majority of pianists and technicians who have taken the time to familiarise themselves with the dynamics and performance potential of this fully revised version of the modern grand piano action. The regulation procedures and the majority of the regulation specifications share much in common with other contemporary modern grand actions.

At this time, a number of high-end piano manufacturers have expressed an interested in trialing the Overs action, with a view to using it in their grand pianos under licence. One leading manufacturer has already committed to making a full appraisal, and may well choose to offer the action as a higher performance option to the standard Renner action. It is highly likely that in time the Overs action will become the default-standard grand piano action design for the majority of the world's grand pianos.

While it is intended eventually to make the action available to approved technicians for retrofitting under licence, negotiations with interested manufacturers must be a first priority. Possible methods for distributing to the retrofit market remain under consideration, while manufacturer enquires are now welcome.


First published 5 August 2001

These class notes were originally written for the PTG Reno 2001 convention,
and must not be reproduced in any form without the written consent
of a representative of Overs Pianos.

OVERS PIANOS 2001