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I recently acquired a Young Chang U-116S (45" vertical) as a repair and regulation project. I live in a humid climate (Cayman Islands) and the piano has been obviously exposed to some extreme heat and humidity although inside seems in very good condition without much obvious wear or corrosion on action/strings. The only obvious thing wrong was the key dip was about 1/2 of what it should be. After storing the instrument in air conditioning for a few months I have disassembled and discovered after removing the rail assembly that the keybed has a high point running under the area of the front rail which is fairly noticable (varies up to 3/16"). I am guessing the high spot corresponds with a lamination in the keybed and no wonder the key dip was shallow. Prior to doing anything else, it made sense to level the keybed (with a belt sander and straightedge?). Any advice on the best procedure for key levelling given the problem with the keybed?

Before doing anything else to the piano, how old is the piano and is it still under warranty?

Also, are you a technician, student, hobbyist...?

Edit: You say the keydip is 1/2 of what it is supposed to be. Is it only shallow in the middle, or across the whole range of the keyboard?

Sometimes the front rail is shimmed up. Check this first. If the keybed is warped I would expect the key height to be messed up as well as the key dip. Sanding down the front rail sounds drastic to me.

Pictures?

Joe, Ryan - sorry I guess I have not described the problem very well and I am not sure a photo would help much but may take one tomorrow. This piano is a used 'project' piano, not under warranty[!]. I am an semi-pro tuner currently learning the finer points of rebuilding and repairs on 'patients' purchsed for this purpose [I do not want to experiment on clients' pianos]. I had no intention of sanding the rails of the key frame - the shims typically used to level the key frame assembly [to adjust key height] are thin [maybe a 1/32" or so cardboard or veneer]. This is a bigger deformation of the 1 -3/8" thick mahogany keybed that everything sits on [probably due to moisture]. I have removed the key frame [rails] and putting a straightedge across the bed indicates a hump across the full width just under the front rail. The deformation seems more noticable on the top side than the underside which is still relatively flat. This suggested to me trying to level by grinding off the top surface rather than clamping to try to flatten it. Reblitz in his description of the "Keybed" [Illust. 2-38] shows the keybed being removed from a vertical piano - I now realise that the entire mahogany piece can be removed from the cabinet arms by loosening a few large screws on the underside. I will assess it once it is out of the piano. If it can't be flattened any other way, perhaps I can take to a cabinet shop and have it run through a planer to accurately flatten the entire surface? Since the key bed height relative to the other action parts is set by the side cabinet arms that the keybed attaches to, it seems to me that changing the thickness would make no difference to this height when it is reassembled. I guess I am looking for advice someone that has actually made this repair previously. I doubt this is a very common problem however Reblitz refers to it in his manual but does not discuss solutions. I appreciate any useful advice, particularly if you have encountered a similar repair scenario.

Gents:

Here is a few photos which should explain the situation. The one with the keyframe shows the gap under the front rail caused by the bulge across keybed underneath. I have laid a straightedge across the surface which should help you see the surface bulge.

Thanks in advance for your comments.

Wil

Cut a channel through the lamination down the centre of the bulge, using a router or whatever tool at your disposal. Reglue and clamp, then sand down.

Merci Jean - that sounds like sensible woodworking advice. Assuming it is a split at the lamination, simply sanding it down may only be a temporary fix...by regluing the joint underneath that will definitely help it become solid again. After gluing I will clamp it in both directions to be on the safe side. W.

It is difficult to assess from the photos whether there is a separation in the laminations of the keybed which is causing a bulge in the top, or the entire keybed is warped. I know you said that the bottom of the keybed seems flatter, but that may just be from the difference in the way you view it compared to a straightedge.

The suggestion above is good, but you might even consider putting a series of grooves in the bottom of the keybed so that it will be held flat by the piano's cheeks. You could even use a circular saw for that, with a plunge cut. After you do that, consider using extra screws to hold the keybed flat against the cheeks.

My impression of earlier pianos of this make is that the wood was not particularly well seasoned, so doing something like that may help it resist the tropical climate.

You can also drill a few holes right through the keybed to inspect it. 5/8 inch.

Jean - I drilled an inspection hole which was useful. It appears that the keybed is composed of particle board with only a veneer of mahogany (approx. 1/8") top and bottom. I am guessing it is a single block of particle board and not laminated at all. It is hard to say what made if bulge in that particular place. Given that it may not be a laminated assembly do you still think gluing will be necessary?

Hard to tell without seeing it. It looks like the top veneer has become unglued, so reglueing would be my bet.

Have you removed the keybed from the piano? If so, before doing anything, I would cover it with a heavy blanket, lay it on workhorses, and put a heater underneath and dry the heck out of it for 24 hrs. Then proceed.

There may be moisture in the particle board that causes it to swell. In that case, it might just be best to cut it all out and replace it with a more stable material, like a few layers of a good veneer plywood.

I agree

I'm not fully understanding your problem. The 'key frame' usually is leveled over the keybed. If your experiencing too much movement of the keybed I would suggest adding some stabilizing support beams on the underside.

The the key frame often warps. It is not uncommon to address the center rail by installing shims and tightening down the ends of the rail to create spring tension.

From what I've read, it appears that the keybed is made out of particle board which has absorbed some moisture and is now distorted.

I do agree, though. I'd try the simplest approach first. First shimming the keyframe at various places (probably the balance rail in this case). Then, test to see if the cabinet can be made to accommodate the new position of the keys. Though the keybed may be warped now, it may be stable in its new condition if the piano's environment is kept consistent.

If the keybed continues to change shape, or if the cabinet cannot be made to accommodate the shimmed keyframe, then the keybed can still be replaced later. Edit: You've only lost a few hours time.

Edit: Replacing the keybed will involve reinstalling the action bracket supports. You will need to position the keyframe very accurately. You will need to drill holes for the keyslip and cheekblocks. You will need to veneer and match the finish of the piano's case as well.

I agree. Replacing the keybed is only if the present one is unstable and cannot be made stable. I would even consider, after drying it out, cutting out sections, much like older key beds and soaking it in epoxy. Or many other alternate solutions. I don't think it is possible at this point to just fit the keyframe with shims, etc...

Another solution could be, if the keybed is now stable, too simply reinstall the keyframe and basically bolt it right through the keybed.

I'm just brainstorming. It is difficult not having enough info. More pictures would be helpful.

Thank you all for your suggestions - each one is interesting and useful. As an 'exercise' for me in repairs this has made me think about the nature of the materials involved and expedient vs time-consuming [though permanent] solutions. For a client with a piano that may only be worth $1000 it might be overkill to try to re-build it but this is a non-profit project with the luxury of unlimited time. Perhaps some combination of approaches may be a 'practical' way forward. If the simplest approach does not work as Joe suggests, I may simply build a new keybed from glue-laminated hardwood. I could always salvage the finish strip matching the cabinet by cutting it from the original keybed and use the old keybed as a template for locating the keyframe and action bracket supports in their identical locations.

Looking at my 'test hole' [thanks again for that suggestion Jean] there is no gap evident between the particle board and the surface veneer indicating to me that cutting and re-gluing may not solve much since the PB has simply swelled and is permanently distorted. I intentionally dried it out for months to see whether that made a difference but it did not. As a composite approach, I may try reducing the worst of the keybed bulge by sanding and then try re-levelling the key frame using additional shims as required at the balance rail.

Good plan.