Piano World Home Page Forums Our Most Popular Forums Piano Tuner-Technicians Forum cheap sponge instead of felt?

Using a bit of a cheap sponge as back rail cloth instead of felt eliminates the bounce in my keys. Is sponge ever used? What legit material would do the same? I know I'm trying everone's patience here but folks, with your help I'm nearing a resolution

I've tuned a few newer Kawai uprights that have a layer of some kind of sponge/foam on the hammer rest rail... Not sure if you can find something similar. It works really well.

Ron Koval

You would need to be sure that it does not degrade and become powdery with time...

Thanks. That Kawai stuff sounds the ticket.

I restored a harpsichord that had been built with foam rubber rail padding, key punchings, and so forth. Everything had disintegrated. I second David-G's advice.

Yamaha uses a foam rest rail on their upright players because the bouncing interferes with the playing system.

Wow! Just what I need. Any manufacturer's names? Thanks

Just ordered some random foam from eBay. Time to experiment!

What sort of foam have you ordered? Could you share a link? Thanks

https://www.ebay.co.uk/itm/232600860764?var=532010422080

Just a soft 42X42X1/2" I didn't look too long. I'll see if I can find something 1/4" and maybe soft and medium to try as well.

I've contacted the guy. Meanwhile here's 1/4"

https://www.ebay.co.uk/itm/123311052334?hash=item1cb5e9562e:g:C4wAAOSw0d1cETHD

You are aware that if you put something of different thicknes there, your key height and whole action regulation will be off? If you put something thicker key height will go down, key dip will be reduced, damper - key timing will change and if you have single repetition action as you are claiming you have, there will be no lost motion and hammers will rest on jacks, so it will not work

That"s why I need a variety of thicknesses and densities. I'll start experimenting with a few keys in the bass.

I have no idea if it has the right sonic/mechanical qualities but for a high quality foam unlikely to turn to dust I recommend something like 'Plastazote'. This is a resilient pressure (nitrogen) blown sealed cell structural foam I used for making custom fittings on white water open canoes. It is also used in healthcare for supports and artificial limbs etc. as it's stable and durable.

Thanks. I've ordered some from ebay. I see they're used for sole inlays. I never thought of trying those!

Perhaps using plastazote as an under-layer beneath felt would get you the resilience you want and minimize the sound of the shanks coming to rest? At $40 for a sheet, pz is hardly "cheap foam", but if it does the job you need...

I'love report back once it's arrived. I'm only going to test it on one key/hammer. That'll be enough. Meanwhile I think I've spotted my original problem - I have no back rail! Only a balance pin rail- at the back nada!

When I bought the foam for my bench the sales person explained that the quality of foam, including it's life expectancy, is determined by its density. So she sold me the heaviest foam they had for couch cushions. I found this article that is consistent with what she said. It may help you find a foam that will have the longest possible life.

That may be true for seat cushions but it isn't appropriate for everything and it takes no account of the higher quality materials available. For instance if you get a decent quality pressure blown foam camping mat (such as the yellow Karrimat ones) and make a cushion from several layers of that it would (probably) last many times longer before deforming than standard cheap chemically formed cushion foam.

I doubt any foam will last as long as wool felted cloth.

I'm more interested in its damping properties. As it's my own instrument it can degrade all it likes.