According to Reblitz one should align the back of the jack to the back of the wood core of the knuckle. In many pianos the jacks aren't parallel to the wood cores of the knuckles. So I don't think that method is very reliable. Is there any other way?

On my Bechstein model M, on the top of the repetition lever there is a very thin groove on either side of the opening for the jack. These grooves are coincident, meaning they line up with each other making a straight line interrupted by the opening for the jack. Is it a valid procedure to align the back of the jacks to that line?

No, that is not what that groove is for. First you must make sure that the jacks are centered in the repetition window, and not rubbing either side of the window.
There are two methods to regulate the jacks to the knuckles. Method #1. Regulate the first and last jacks of each section(bass, tenor, both trebles),Than run a thread weighted on both ends across the back edge of the previously regulated jacks. Then regulate all the jacks in between to match the end jacks. This is the hard way.
Method #2. Put the action on a flat level work bench. Shim up the front rail of the action so that the dip is the same from end to end if needed. With the action turned around,(looking from behind the hammers), regulate each jack by looking in and depressing the rep lever( you must keep the hammers at the correct height, because depressing the rep lever will cause the hammers to sink lower), then regulate the jack. Leave each hammer you finished regulating in the raised position and go on to the next one, and than the next ect. until your done.

If the geometry and regulation is right, the jack should be at 90 degrees to the hammer shank at rest. Or close to it. The angle changes as the blow distance changes due to hammer wear. Really what you are looking is the center line of the knuckle. Imagine that line to be wide and set the back of the jack to it.

kpiano

Thanks, both of you!

So I should regulate the lever height and the blow distance first, and then the jack? Perhaps I should test to regulate the lever height and blow distance of one key first to see that the jack regulates correctly, and then choose a new blow distance if not.

My experience tells me that there is one important criterion for this adjustment. If you hold the hammer so it cannot rise, the jack should stay under the knuckle as you press the key. If it is lined up with the core of the knuckle and the jack slips out, or use any other method, it's wrong. But it still may be a good rule of thumb.

Once you have assured that, you could set all the keys so that they hit the letoff button at the same depth, but it is really easy to spend too much time regulating an action to the point that nobody is likely to see any difference, and that would be one way of doing it.

That is right BDB, but I think that the acceleration will be maximized when the jack is perpendicular to the shanks.

Randy Potter says to regulate the jack to knuckle then blow distance. Blow distance has to be "in the ballpark". If the hammers are down on the wippen cushions you had better bring them up or the knuckle won't be anywhere near where they were. You have to make a refinement circle so in a sense you are setting jack position both before and after setting blow distance. Then because the rep spring adjustment affects the rep lever height and the jack position, another check of the adjustment might be necessary before it is right.
kpiano

The repetition spring doesn't affect either the lever height nor the jack position significantly, but you can't get an accurate lever height if the tension is too weak.

Reread what I said about spending too much time. If you spend so much time on these things that your charges become so high that customers hesitate having it done, you aren't doing anyone a favor.

Blanket statements like the one BDB made are not good. Everytime I think something is not going to affect the regulation very much..... I have found that the rep lever height changes a lot in some actions when you set the rep spring. Obviously you regulate one note comepletely to see what the adjustments do so you don't waste time making an extra refinement circle. Still the action doesn't play right until you nit-pick through the last circle.
Blow distance is a relation to key dip. Set the key dip to what you like, 10mm or a little more is usual and then set blow distance so the hammer has enough travel to take it through letoff. You can set letoff at anytime, it doesn't change. Then make a circle through all the other adjustments, maybe two circles, and then refine the aftertouch by adjusting the blow distance. You have to leave the angle of the jack to knuckle at what ever it ends up at. You can compromise the keydip if the action plays significantly better with a shallower or deeper dip but I like a certain dip when I play. 3/8 dip isn't fun.
kpiano

Some technicians, including Franz Mohr, prefer to adjust the aftertouch, by changing the dip. Why do they do that?

In the Baldwin concert prep class offered in the 1990's, aftertouch was one of the last adjustments, made by altering the key dip. They gave us a penny with a hole drilled in the center for the front rail pin. We put the penny on top of the front rail bushing and adjusted the dip till we had a "penny's worth of aftertouch". This method would be more accurate than adjusting the aftertouch via blow distance.

Having said that - the blow distance alternative is much faster, and suffices for average players and average pianos. It's a quick way to make an action complete the cycle when there's no time or money for a full regulation.

Yamaha is resolute on 10mm as keydip and so the aftertouch must be adjusted with blow distance.

It would be easier to make a small precise change in aftertouch at the front of the key than the back. Afterall, the key has twice as much room to move at the front.
Rick Davenport in his regulation class used the capstan to give the action the finishing touch. Actions like Yamaha seem to respond to that final adjustment well. Some others don't. se la vie

kpiano

Just what is that groove for, anyway? I suppose if you adjust one jack properly and notice where the jack is relative to the groove, it would allow other jacks to be more easily set in the same relative position.

He groove is cut as a guide in the manufacturung process.
The jacks should be set to each individual knuckle because it is rare to find the knuckle of every shank glued at precisely the same distance from the centerpin line.

Curry wrote:
The jacks should be set to each individual knuckle because it is rare to find the knuckle of every shank glued at precisely the same distance from the centerpin line.

Indeed, and knuckle position variation can cause large variations in the hammer/key ratio. When this variation is significant, I believe it is worth pulling the knuckles and refitting or replacing them. A +/- 0.5 mm variation in knuckle position can cause a 5% variation in the hammer/key ratio.

The length of the knuckle tongues also can vary considerably. This causes friction variation between the jack/knuckle contact, since the jack/knuckle-contact offest from the hammer to wippen centre pin line will vary from note to note. Even when fitting quality knuckles from Abel, we first sand the knuckle tongues to a uniform height using a disk sander and jig. One of our common action modifications, to reduce friction, is fitting 9 mm diameter knuckles in place of the usual 10 to 10.5 mm standard units (drop screw to hammer flange clearance needs to be watched when fitting these smaller knuckles). But they can very much improve the overall level of action friction. Very often the 9 mm knuckles have tongues which are too long to allow them to be fully seated in the hammer shank slot. In this case we disc sand them down to allow the tongues to be fully seated.


As Curry also mentioned the repetition lever groove is cut at the time of manufacture. In theory, this groove is intended to represent the ideal position of the jack for alignment with the knuckle. But variations in the manufacturing tolerances of the wippens and the action spread distance will ensure that, in practice, the groove should be ignored. The jack position is probably best adjusted using the second method Curry mentioned in an earlier post.

Keith Roberts mentioned that Yamaha is resolute on a 10 mm dip. They are one of the few companies who can be particular about consistent dip, as they take considerable care to set up their actions with a consistent hammer/key ratio. When there is variation in the ratio, each action will require an individual relationship between blow distance and key dip to achieve an optimal aftertouch.

I've probably meandered off topic during this post David R, but keep looking at your action - the solution will come to you.

Best regards,
Ron O.

Hello Ron. How have you been? It's great that you are posting here.

Hello Curry,

I've been plugging away building our next piano (a 225 which is coming your way - sold to a client in Boston), rebuilding a couple of grands (a Kawai KG6 and Baldwin SD-10 - both are modified) and preparing for the development of our 280 and 196 cm pianos (planning to begin production later next year). I've had a few people mention this forum, and looked at it a couple of times. Will you be going to the national convention at Rochester next June? We will be exhibiting the piano we're building at present for our Boston client.

Regards,
Ron O.

Ron, your work certainly keeps you busy. The SD-10, one of my favorites, will certainly turn out to be a winner.
I will mostt likely be in Rochester. We will meet again.