Regulating Hammer Letoff

[goodenbp]

I have purchased an old German piano with a 3/4 frame and overdamped action. Delightful woodwork, and for a novice, has been proving to be absorbing in learning to fix it and begin to learn to tune it. Three screws hold the action in place and it can be removed as an entire assembly making it much easier to work on. Clearly someone has previously had a go at adjusting the action. There are additional (red)felt pieces under the middle sections keys, (so the keys sit slightly proud in the middle) The screw adjusters seem quite far out as you can see in the picture of a key. I can't imaging they designed it like that. In spite of this, the hammer let-off is typically around 20 mm. Now the Reblitz book, as does the Haynes piano manual,say that the measurement should be around 3 mm. No where near my 20mm. All notes do play, but some were blocking and after backing off the screw shown in the picture, are no longer blocking.
My question is: would that 3 mm figure apply equally to old(around 1890) pianos with overdamped actions and should be what I aim for? If that is the case would this indicate the backfelt and possibly the balance rail washers are compressed and these need the attention first? Is there a standard thickness of the backtouch felt and rail washers?
I have one other issue to mention for interest. Access to the strings for muting during tuning was difficult with the overdamped action. In the end I "tuned" it with the action removed and by plucking the strings like a guitar. Now I will grant this is not exactly quick but it was my time for myself. Will this incur the horror/mirth of the experts on the forum or is this an acceptable method?
Brian

[Colin Nicholson]

The screw under the pieces of felt have nothing to do with set-off (or let-off) - this will have been set at this height previously because the leather notches are worn away under the hammers - these are capstan screws. The extra piece of red bushing cloth is presumably there because the screw has reached the end of its thread (or tether!(?

The keys sitting proud will be adjusted by the centre rail - nothing really to do with those felts.

Best to leave backtouch well alone - once you start to change the geometry of the action ratio, it wont work properly.

How are you adjusting the set-off?
Do you know where the set-off rail is?.... and do you have a tool to adjust it?

Not the right procedure for tuning overdamped pianos - but if you are happy with the results, fine. Best to let a piano tuner do that bit!

[Colin Nicholson]

During doing some action work on a piano, I kept saying to myself.... "20mm" ? (referring to your version of set-off).... then it dawned on me.... I think that you are referring to the back-check distance after the hammer has rebounded from the string? This is not the set-off adjustment, but called "checking". It is usually around 15 - 17mm on most pianos, but if the leathers & back check felt are worn (or badly grooved) as they meet, then this distance from the string will be considerably more.

To adjust the set-off, you need to remove the damper rail/ lift wires - as one complete unit (2 screws at the top), so you can see over the top of the hammers. You'll never be able to adjust set-off properly by simply peering through the bird cage.
The set-off screws are the tiny little wooden buttons that sit above the jack toes (or knuckles) - and with most old pianos, these screws are probably seized or very tight. You'll also need a set-off tool to adjust them.

Might be a case of "back to the drawing board" - and refer to Reblitz again.
Your picture above & various explanations about (your version) of regulation dont really make sense.... with respect. You are best regulating the action without the damper rail on first: then put the rail back on later - but take care not to break the little damper buttons that are pinned to the bodies at the top.

If the leathers are worn, then this screw position (which is far from normal) has been adjusted like that to compensate for worn parts. As an experiment - try to wind one right down so it is flush with the key capstan.... then play that note.... and see what happens.

[goodenbp]

Thank you for your helpful comments Colin. I am appreciative of your time. You gave me the confidence to remove the damper rail. I should have done it earlier for the improved access it gives.
I note that the gaps between string and hammers after striking and holding a note, are all over the place. Anything from almost damping the strings to up to 22 mm worst case. I assume this is the “checking” measurement you refer to as normally being 15 to 17 mm. Clearly there are some issues there that I will need to address.
I confirm my earlier estimate of set-off or let-off. (holding the hammer with slight resistance as the key is depressed until the point where the jack releases and measuring gap to the strings) These distances as mentioned previously were found to be a lot more than the 3 mm mentioned in the books. (Reblitz 2nd Ed p 166) Given that all gaps are consistently well in excess of this, I had been loath to alter them, hence my previous post. Does this measurement apply to all pianos? I have made my own thin shafted tool for adjusting the difficult to access set off screws and am very fortunate that the few tested are turning easily. I adjusted one a lot to verify that I could get it to release at about the 3 mm mark. However since they are all so far off, perhaps it is best left for now knowing that set off correction is possible after the other issues are sorted.
You refer to the wearing of the leather notches under the hammers. If I have understood you, this would be the “hammer butt buckskin” that the jack pushes on and it makes sense that the capstan screw has to be adjusted to compensate. However to the eye, they look surprisingly good and do not appear worn or compressed. Certainly not to the extent that the capstan screws have been extended (1-2mm) combined with an additional layer of felt (1mm). The thickness of the buckskin is only about 2mm.
I also note that the red felt balance rail washers are all “home made” clearly hand cut with scissors from very thin (1mm) felt. There are no front rail washers at all. The backtouch felt is 5 mm. None of these are the original 120 year old material. So it has been replaced at some time. I do question if with the correct materials. I did a trial on one key doubling the balance rail washer height to 2mm and increasing the height of the backtouch to keep the front of the key from rising. The capstan screw could be backed off accordingly. The action seemed better.
I can’t help but wonder if with correct balance rail washers and thickness backtouch felt it may make it possible to take out the extra felt layer that has been glued over the capstan screws and reduce the extension of those screws. You cautioned against changing this felt. I could perhaps try a thin temporary layer on top of the backtouch felt. The washers are easy to change back if required.

[Colin Nicholson]

Sounds like you are getting into this regulation lark! well done.

When you remove the damper rail, if possible, make sure it is stored in the same horizontal position as it would be on the piano - eg. laid between 2 chairs, so the wires hang down naturally. If it is stored on its side or back, you risk damaging the wooden buttons, and more important, the weight of each damper (if lead weighted) might "shunt" all the flanges to one side if slightly loose.... so also make sure all 65 (or so) flanges are tight. When you put back the rail - you might find some have moved slightly, and the damper felt's grooves dont align with the strings. Flanges should have been checked before removing the rail.

One of the reasons for the highly adjusted capstan screws may be that a thinner back touch baize has been fitted.... even 1mm makes a huge difference. Also, with compression & shrinkage of materials & parts, the box cloth flaps on the screws may also be compressed. I know also that some german pianos have an aftertouch rail at the back.

If you aim for 3mm set-off, that should be ok. If the jack trips too soon, you may lose performance.

Yes, the checking will probably be all over the place, especially if there are no front rail baize washers. The key should travel down about 9.5 - 10mm - using a depth gauge from some verniers if you have some. If the check felt is worn, or if they dont strike the hammer balance leather evenly & squarely (resulting in a groove on one side) - then you need to bend the check wires forward slightly.... however, its difficult to envisage everything if wrong materials have been fitted.

Its quite common for balance rail felts to be square on some german pianos - usually blue..... and the front rail pins may be "carpetted" with a long length of baize with holes cut out for each bat pin. Eg.. some Schiedmayer pianos have this arrangement.
I would be careful changing these, so not to change the height of the keys.
Are there any card or paper washers under the keys?......
You may need to buy some baize washers for the bat pins (these are at the front of each key). Let me know the key dip? - how far the key travels down - using a neighbouring key as a guide.

[goodenbp]

This is a bit like restoring an old classic car to concourse condition. As you go you uncover various repairs and deviations from the original manufacture and you have to decide how to get it running sweetly.
The key dip is a fairly consistent 10mm +- 0.5mm on all keys. There were no front rail punchings or strip as can be seen in the picture and no additional paper/cardboard washers. I think I will set up a few keys with various thickness temporary materials to confirm that I can simultaneously achieve good key height, correct key dip, combined with required taking up of lost motion, checking and letoff. That way I will know what thickness materials to purchase.
Once again I do appreciate the very helpful advice you have given me.
Brian