Piano World Home Page Forums Our Most Popular Forums Piano Tuner-Technicians Forum Knuckle replacement

Soon I'll be working on an 80-year old grand action that is amazingly clean, and that was hardly played through the years. There is absolutely no reason to replace hammers, shanks, or flanges. Hammers sound great and just need reshaping. Flange pinning is already close to where I want it; will be easy to optimize. Shanks are straight, and only a few need minor traveling. Somehow the wood is still a fairly light color.

I would like to replace the knuckles, though, so I can get the best regulation possible.

Any suggestions or tips for this work? How do you prepare the shanks for knuckle removal? I'm thinking warm water w/ a bit of wallpaper remover, and maybe some heat via a soldering iron if necessary, but wonder if the slit in the shanks might change dimension as the wood dries, complicating the fitting of the new knuckles. I will of course be using hot hide glue to install the new parts, and I also want opinions on nap direction, which seems to be almost evenly divided as I peruse older posts on that subject. (My instinct says put the buckskin nap in the same direction as the jack pushing up on the knuckle to minimize resistance, which I believe is the more "European" approach.) Any thoughts appreciated.

Knuckles can be removed - not not. Some techs saw off the old knuckles and cut a new slot on a table saw with thin blade (using a jig of course). This is also the best way for re-positioning knuckles if needed.
Old knuckles can be removed without any heat or moisture if the glue is old and brittle. Cut/break away the old glue collar and pry/lift/work the knuckles out with a pair of knuckle removing pliers. Proceed methodically to avoid splitting shanks.
Sometimes the new knuckle cores are too thick for the old slot. In that case, squeeze the core in a table vise before installation, as soon as the glue moisture hits it, it will expand again, ensuring a tight fit.

Let me know if you're interested in re-positioning the knuckles, I have a jig. I also have some knuckle-removing pliers if you want to borrow them. Assuming you'll return them

Assuming what remains in the wood is secure enough, if the saw line for the new knuckles have to be done inclueding a part of the old core, I would not trust the solidity of the whole assembly.

For sure the best knuckles are thicker than the old ones, very often, but what is more annoying is that they may be taller (particularely on Schwander shanks)
Not ideal for repetion, nor for the stability of the roller in time (ofen I have seen knuckles bended or hallf unglued due to the not deep enough recess, plus too large overcentering (Older Bechsteins with Schwander action)

as the wood of the core is hard when compressed it may break apart, you did not notice that ? (I tried that compressing without much success )

I prefer opening the shank a little more .

I'd like to see how looks that jig to work the shank . I have seen some designs in old issues of the PTG Journal, but I dont really remind how they where.

Generally, what bothers me with old shanks is that the bushing cloth is too dry and non resilient to allow for a good consistent repinning.

Changing the cloth for all shanks is possible indeed, a little time consuming, a little tricky , good cloth is necessary. at that point I generally decide that new shanks will be a better option. If the heads are kept (refelted or just sanded) sure new cloth for the centers may be an option
(pinning also is to be done with a support so the center is square to the shank - less papering... long 60 cm centers is what ABel uses if you ask for rebushing/centering job, better consistency than with small centers , but I believe those centers are not sold in USA.

Old pianos had smooth knuckles, with anice thick leather and not too hard underfelt.

I heard of methods to repair the shape (impregnation, probably, reinforcing)
Sanding the leather is possible, also, if dirty, so a "new" nap is made.


Problem with old actions that did not play is that when they are used the parts show their age, centers, cloths dont stay neat and clean under use , in my experience. Old cloth was sometime excellent, but when the fiber is dry all the little scales that allow the felt to hold together are brittle and fall in dust... That said I have met strange incredible bushing cloth, very springy and that did not wear much because of that.

I use knuckle removing pliers which just snap the knuckle out of the joint. Works very well.

However, I find the process of gluing in knuckles by hand to be less uniform than what is done in the factory. It can be done, but in most cases I would question why. Now that WNG shanks/flanges are available, I'd be inclined to replace anything wood.

Just because hammers have lots of felt, doesn't necessarily mean that they work really well (or even ever did).

I believe it is a rare case where simply replacing knuckles is really the best choice. Your situation may be one . . .

It is possible to remove the knuckles without removing the shank assemblies from the action, but you will need to be careful not to damage the shank/flange centers. Use soldering pliers to heat the sides of the knuckles and then pry them off. Be careful to not scorch anything. There are also knuckle extracting pliers... never used them before, so I can't comment on how well they'd work. But generally, I agree with the post immediately above mine.

I use a knife to cut the glue loose from the bottom of the shank, and then diagonal cutters to lever the knuckle out from one side, and then the other, or I use a bandsaw. But I think the benefits of knuckle replacement are overstated.

I have peeled off the old worn knuckle leather and glued a wrapper of new leather to a whole set of shanks in a 100yo grand, then regulated. The piano still works fine when I have revisited.

when you compress the wooden core, often the glue joint break apart. strong pliers are better to do that I have cutting pliers with multiplication of strenght, filed them so they crush the wood without effort

I also made a support gig with a sort of blade that can be tapped with a hammer, works well but after some occasional breakage I stopped using it (the jig under the shank must be really flat and hard enough, with a recess to receive the knuckle).

Greetings,
If the knuckles need replacement, how about the back-checks? If the knuckles are not worn, why replace? A quick swipe with 320 paper will usually put them in proper shape for any regulation that an 80 year old action could justify, and , 80 year old hammer felt is not going to behave like new, so be prepared for rapid wear if the piano suddenly starts getting used a lot.
Don't remove the knuckles with the flanges tight, you will damage the pinning, at least, on some of them. Use the proper pliers, or make your own, and just make sure the nap is all going the same direction. I would recommend Escaine over leather, as it is more durable and quieter.
Regards,

did you make clamps with PVC tube ? the shape is obtained by the under felt, so on old parts I am unsure it can be done well as the center compress in time more than the edges

I've used wool yarn pulled through the bearing area of old knuckles when they are compressed slightly. Depending on the condition of the knuckles, that's often enough to get many years of solid regulation out of an old set without fussing with replacement.

I tried, indeed there is a good result. I try to avoid those kind of things but they are good in some situations, and the gain in power is noticeable.

Is not it better to insert a thin strip of thin cloth ? more predicteable shape ?

That , under compressed whippens heel, makes wonder for the touch...

Thanks Zeno, I'll bring you some bushing cloth as collateral.

Thanks for the replies, everyone. The backchecks are in decent shape, better than the knuckles, which are slightly flattened, loose, and full of graphite. I could sand and bolster (and still might do only that) but feel like knuckle replacement would greatly improve the feel of the action through letoff - enough to justify the work and minimal expense involved. In NYC, I simply never see old actions in this kind of condition - a pleasant discovery.

If the owner can't get at least 3 years of use out of these original hammers I will be very surprised (and there is definitely enough felt remaining for 2 reshapings) so it buys time if nothing else.

Let's also bear in mind that not everyone can lay out $1500. for new hammers, shanks, and flanges, plus the cost of regulation - especially musicians living in New York City. That's a lot of rice and beans. (Or 2/3 the rent on a one-bedroom in a funky neighborhood.)

I have to regulate a piano with recently replaced knuckles. There seems to be far too much resistance as the jack escapes when many of the keys are depressed slowly. How do you assess "the feel of the action through letoff"?

(some) New knuckles may need a good brushing and rubbing of Teflon powder or talcum. If the knuckles have the nap inverted there is much resistance too.

Letoff should be smooth.. Only at real speed it is more resistive . Indeed it depend also of the geometry of parts, and hammers mass, and centers. Friction during letoff can be modified with regulation, stack location. For instance the higher the shank is at the end of letoff, and the less the friction between jack and roller.... If unsure, I lmeasure how much up weight and down weight I have just to be sure I have not a problem with friction and ratios before let off.

I've used either strips or wool yarn, or both depending on the shape of the knuckles. Not everyone can afford complete replacement.

Thanks for your advice, Kamin. I hope it's helpful to James too.

I like the kind of operation that allow to have the instrument better for some time without the cost of the real repair, but I generally try to avoid the same instruments, because if I need to work on one I spend generally too much time.

At some point what you ask to the customer is better kept for the future repair
With time I learned how to organize the job so the due repairs are done a few years later, then I try not to do things that will need to be undone later (as bending the balance rail pins to level the keys if the mortises are due.)

We have so many actions in regulation/tuning/voicing that have to be done twice or more, so I focus on the one that will be useful for long term.

Shaping old dry and non resilient hammers and voice them is typical of the things I do roughly , when I know the heads and shanks will be changed.