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Joined: Jun 2021
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I acquired a used Yamaha Clavinova CLP-120. It had quite a few sticky keys, and upon disassembly and inspection it appears that at least 11 keys are cracked, but thankfully most of them have not chipped off.

I want to repair these keys myself using glue, since replacement keys become expensive when you have to buy many (about €10 a piece), and I may even have to buy more keys down the road.

The question is which glue? I see some using superglue, but maybe some kind of epoxy would be better suited for the compression forces the joint will experience? I have a suspicion that regular super glue may crack more easily.

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It depends on where the plastic is cracked.

If the hinge area at the back end of the key is cracked, forget it. You'll need a new key.

If a crack is in a thicker part of the key then try epoxy.

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Mac has done a lot of repair on his Yamaha so has an informed view on repairs. New keys may have better materials and/or design so would be ideal repair, but are expensive. Some parts of the keys may not be repairable from a practical perspective

One challenge selecting adhesives is identifying the plastic and coating type. Another is that the materials deteriorate over time, so may not react with adhesives as expected. Some adhesives could cause a failed bond or melt the plastics, for example.

-- For a start, the Japanese require a materials labeling stamp for plastics, which might help you identify the materials used on the key. I don't think it helps with coatings.

https://en.wikipedia.org/wiki/Recycling_codes

-- You could call Yamaha and ask what type of adhesive they recommend. They probably won't answer you but it is worth asking.

Without seeing the key, I would try a 2-part epoxy "marketed" for plastics. You can look at the technical specifications to see which materials are n/a. You can test a small amount in a non critical area of the key to see if this is a complete disaster.

Depending on the crack, I might consider adding a "support beam" like they are using on the I-40 Missippissi bridge. But that might add a lot of weight or be useless. . .

Study the instructions and warnings of the epoxy. A few things I might consider:

- Roughen the bonding areas with a Scotch-Brite pad or fine sandpaper, then scrub with high % isoprop alcohol to clean (wear gloves so oils on skin don't contact the key).

- When epoxying, wear gloves and have great ventilation.

- Strict ratio of resin & hardener per instructions. Mix the two parts extremely well else get a lousy bond. Typically short pot life means that you should use small batches; don't use epoxy that is starting to get thicker, just mix a new batch.

Risks of DIY adhesive repair include:

- Destroying the key

- Bond fails

- New cracks emerge near the repaired area. Original breaks likely are in areas of physical stress, poor design, and/or poor materials.

- Depending of the area of damage, the weight of adhesives (and/or poor repair alignment) could impact the playing experience.

https://dm.henkel-dam.com/is/content/henkel/tds-us-loctite-epoxy-plastic-5-min-final

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I guess I'd use two products.

Super glue to have an exact match/bond with the two (or more?) parts of the key so that the key is in its original shape and size and then also some epoxy around the joint assuming that a small amount of it weighs basically nothing.

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With solder gun (fine tip) on opposite side lightly, no pressure. Crazy glue topside. After drying if surface is not even, soak WD 40 on cotton q-tip and spread lightly to even any bumpy formation on top.

Last edited by lgarcia; 06/17/21 12:34 PM.
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Maybe this is obvious, but just in case not… can keys be swapped between different notes? So eg if C3 is broken can you repair it good enough, but also swap it with C7 that you use less and with a lighter touch? Maybe if the key itself is weighted you have to swap the weights too?


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Originally Posted by MarkOfJohnson
Maybe this is obvious, but just in case not… can keys be swapped between different notes? So eg if C3 is broken can you repair it good enough, but also swap it with C7 that you use less and with a lighter touch? Maybe if the key itself is weighted you have to swap the weights too?

I used this approach to fix a Yamaha P120. Glued keys with superglue (and the cracks unfortunately were at the pivot point). Weights are not part of the keys, so easy to swap things around. Worked OK, but definitely a short-term fix.

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@new_pianisto: It would be helpful if you would describe the location of the cracks. Or, better yet, you could post a photo.

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I've now glued 15 keys with epoxy. All the cracks were at the pivot point. Is this what you refer to as the hinge area (at the back of the key)? Will post a picture below. None were broken completely off, but most came almost completely lose upon perturbance with my glue mixing stick.

Will now let them cure for a day or two, and then try to reassemble. Did not do a very thorough job cleaning, unfortunately, except for removong most of the grease with paper. May have to repair them again down the road. At least it seems doable. As they say in Pinchcliffe: Time will show.

A support beam(or "spruce") is an excellent idea, either a thin strip of plastic or cardboard could do, either on the inside or ouside of the cracked area (wherever there may be space). But I forgot this while gluing this time.

Last edited by new_pianisto; 06/17/21 03:00 PM.

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