Replacing Knuckles on a Grand Piano

Replacing Knuckles on a Grand Piano

Sep 22, 2023

Grand Piano Knuckle Replacement (Piano Tuning and Repair)

Welcome to our Series on Piano Tuning and Repair.

The knuckles on a grand piano hammer shank get flattened over time with use and it can greatly affect the playability of the action. This video shows how to replace the knuckles on a grand piano. Feel free to visit our website where you can see other videos on piano repair and tuning as well as purchase parts and tools that you need to service pianos.

If you want to see more of our Piano Tuning and Repair Series, click here to access the entire playlist.

Video Transcript:


Hi there! Welcome to another video from Howard Piano Industries. I'm Steve Howard, even though you can't see me, I'm here. Today we're gonna show you how to replace the knuckles on grand piano hammer shanks.

Knuckle Extraction Explanation

Here we've got the hammer from a grand piano, and this is the shank, and then you've got a flange at the end of it. Right here, this piece right here is the knuckle. The knuckle sits on top of the whippen, and it's pushed up by the repetition lever on top of the whippen, and that makes it go up and down.

There's a slot at the top of that repetition lever that's got a hole in it, that the jack pokes up through. The jack pushes up on the bottom of this knuckle. You can see the shape of this knuckle, it's kind of flattened on the bottom, in fact, and if you can tell from the video that there's quite a deep groove where the jack slides up and down. That's kind of a sign that you should either possibly try to recondition those but most likely needed to replace these knuckles because it really affects the touch, and the playability, and everything of the grand piano action. Today we're gonna show you how to replace these.

It's not too difficult of a job with the right tools, and so forth. We sell the knuckles in our website along with the tool that we're gonna be showing you how to remove the knuckle. First of all, you want to be able to take the knuckle off but before you do that, you want to make sure of course, that you get the right knuckles. There's a couple different sizes, there's I think it's 8 mm, 9 mm and 10 mm what we have available. You want to check the diameter of that.

Sometimes, it's a little hard to tell if they're flattened on the bottom which means they might kind of bulge out on the sides, but sometimes you can kind of squeeze that together a little bit, and get a little more of a round shape to it. Then just measure the diameter of it across the side face of the knuckle. The first thing we were going to do is remove the knuckle from the shank, when we talk about worn knuckles, you can replace, especially if you're replacing the hammers as well. You can replace the whole set of shanks. It's a lot more costly than it is for just the knuckles, but if you have pinning, the pinning on the flange is done as well. Then you kind of gotta weigh the pros and cons of replacing just the knuckle, or re-pinning all those flanges, or just buying new shanks and flanges.

That could be a benefit, maybe cost a little bit more, maybe less work to it so you don't have to replace the knuckles, and do the repenting of the flange. Say you were gonna keep your hammers, these hammers are in pretty rough condition, but if you were gonna keep your hammers and just kind of resurface them, get them cleaned up and stuff, and you wanted those knuckles to work a little bit better. This is a good way to do it, just replace the knuckles.

Knuckle Replacement Process

The first thing we're gonna do is there's a little bit of a glue collar, it's not a collar, but it's a little line there at the front and back where the base of the knuckle goes into the shank. I'm just going to take a utility knife and scrape that off. It'll come off a lot easier if you do it that way. I'm gonna do that because otherwise, don't ask me how I know this, but it can crack the shank and you don't want that to happen. Just a little precaution to avoid some possible problems.

Once you do that, we have an extra tool here. This is our knuckle extracting pliers. We have these available as well but all you're gonna do, it's really simple with the tool, is you're gonna put it down around the base of the knuckle, and then just squeeze. What that does is, that pulls the knuckle right out, fairly simple. Then you can see that you've got a slot there, what we're gonna do is clean up this glue that's left.

Fortunately, this was installed with hide glue, so that makes it a lot easier for taking the old ones out. Here we can see, that we took the old knuckle out, still got a little bit of glue there, but you're disposing those. If you're doing a whole set of knuckles, you might as well use hide glue. It's the hot hide glue, it's the best glue for it. It's not like something you're gonna be doing on the field where it's not convenient to do the hide glue. You can use wood glue but if you ever have to replace the knuckles again, it's a little bit harder to get them apart.

If you're replacing them once, most likely the next time it's done you're gonna be replacing the whole thing anyway. You'd have to kind of determine if you want to use hide or wood glue. I've got my glue pot here ready, hopefully, the glue is a little bit thin but it'll work.

Center Pin Removal

What I'm gonna do is put a little bit of glue here, fill that slot, and then take my new knuckle and put it in the slot. My glue was a little bit thin, it's oozing out on the sides. It's good if you can get a little bit of that glue on the front and the back as well when you're doing it, because that kind of gives us some stability. We put that in there, doesn't take much, just make sure that it's centered. You know from side to side, so it's not sticking out one side or the other.

Make sure you don't get glue on the top surface of the knuckle, because it can make it sticky and not work very well. Once you've done that, just make sure let it set. Usually, what I'll do is I'll set it like that so to let the glue dry.

Over here we've got one that's already, I did a little bit earlier, it's got a little bit of that glue collar. That one's done and this one, I just did probably about 10 minutes ago. It's already pretty solid. Hide glue dries pretty fast, that's the other advantage of hot glue. It dries pretty quickly, so that one's done there. Basically, that's it. You go through, and do that fairly simple process. Again, the knuckles are available on our website, along with the knuckle extracting pliers. If you have any questions feel free to let us know!