Piano World Home Page Forums Our Most Popular Forums Piano Tuner-Technicians Forum Key side play in relation to RH

Hi all,

it's been a while (again)... Been busy here with a brand new campus that we are in the process of moving in to. My life has been more about seizing fires (not literally speaking, thank God ) than fine concert work lately.

Anyways, I'm currently rebushing the keys of a Bösendorfer 200. I have to try to choose the proper felt thickness under less than ideal circumstances. The temperature outside is -13 F at the moment, and the average RH somewhere around 15% (!)

The hall where the Bösendorfer is residing has an industrial humidification system that actually makes quite a good job in keeping the RH acceptable (30-40%). The problem is that I can't rebush in the hall, I have to work in a room where I can keep the RH at 25% at best.

My logic tells me that I would choose a felt thickness which allows just a slight side play, or wiggle, given that I work under dry conditions and that we have a high RH in august (90+ %). Does this feel right? Anybody's input would be most appreciated!

Regards,
Patrick

hi the theory, to me, is that the felt when dry is less thick, but the wood of the key is more tight.

the piano was fitted with leather originally ? then the felt may be thin, as 1.1 or 1 mm, probably (sorry I dont remind the original thickness on Boesen)

finding a good bushing cloth is the main problem. Wurzen make some but sell by large quantity. Renner have some correct, I prefer not to state publicly what I think of the common quality we find. Japanese cloth is interesting, it looks supple at first sight but stay nice in time (content synthetics, the renner is more wool oriented and the coth for center pins is pure wool)

If you have an old key I suggest you make some tests with a micro wave oven (be careful the wood get on fire very soon)

Moisten in controlled space up to 65% ( saturated salt solution at 20°c)

measure and then dry the part (I would cut the key so it goes in the owen.

I did such experiment on wooden flange bushings, not on keys

Hi Isaac, yes they are leather originally. They were quite worn, but I'd guess 1.1 mm.

I reconsidered and decided to go with no play despite the weather, since I find it easier to ease the keys than to tighten them

Good plan. +1

Patrick

By your leave, as I have to rebush the keys on a couple of pianos, one felt and one leather, may I ask the forum some questions prompted by Kamin's post?

1. Is it worth rebushing with leather?
2. Is Escaine a viable alternative to leather?
3. What are the best types of felt and leather or Escaine for rebushing and where are they obtainable in Europe, N America, elsewhere?
4. What glue(s) are best for the purpose?

I would use leather, but did not experiment a lot , I buy strips at Renner, 2 precise thicknesses availeable.

Leather is more noisy, more side play is necessary because the friction is higher, but it does not really wear.

escaine is too thick probably
skin glue is good for that work

Key mortises will tend to get tighter in drier conditions, so I actually prefer to rebush keys when the RH is lower. I don't think you'll have problems working in 25% RH conditions.

I strongly prefer the German bushing cloth sold by Jurgen (Supply) and he has many thicknesses available. He also carries key bushing leather in various sizes as well.

Use the Spurlock cauls for the best results, especially the mortise sizing cauls.

Thank you for your suggestions!

James: I think I use the very same as Jurgen sells, I'd assume that he and my german supplier (Baumgaertel) get them from the same source. I like them, too, they are high-quality stuff. I have the mortise cauls by Spurlock, and some other things too - his tools and jigs make life as a piano tech a lot more easier

Ian: I'm not comfortable bushing with leather, so I will go for the bushing cloth mentioned above. I always use Titebond for bushing work.

Pat, (white/yellow) titebond is too hard, and if your cloth harden it will wear faster, plus more noise. I I suggest you use standard PVCE (vynil) glue, thickened by exposition to air. Or glue for fabrics or for books. I like vynil glue on modern pianos as it makes the job really fast, but if is less easy to unglue later, the hide glue is more usual and adapted to both materials.

Regards..

For cloth in place of leather, the necessity to use a thin cloth bothers me. I I did not really measure but chances are that the mortise is thinner when leather was used.

Be careful that too tight mortise in pine may take years to gain enough side play, and compressed pine wood will swell back. side play on a new mortise may be 0.2 before easing to 0.4 when eased, taking in account the season and the type of key's wood.

Pat, Kamin

I used white/yellow "Titebond Original Wood Glue" to repair a broken hammer shank the other day. Aren't we talking about "Titebond Liquid Hide Glue" or traditional hide glue for bushing felt here?

Flying the flag, Hainsworth weave felt in Yorkshire used by Steinway and Renner. I'll ask them who sells it for repairs.

Yes probaby liquid hide, but vynil glue can be used as long it does not impregnate the felt and harden it.

The advantage is that one can put glue on a long strip, enough for 8-10 mortise, so the job is faster than with hide glue (while liquid hide may do it as well)

Well I made the first part of my HR tests on keys
Took 2 old Steinway keys in pine

from a 50%HR at 22°c , I put them in a bag at 68% HR for 12 hours

One key have yet its cloth in mortise
the other the cloth is unglued

On the 2 keys a Spurlock caul was just holding lightly

I added a 1.1 mm measured bushing cloth in the bag

Result after 12 hours :

The keys enlarged 1/10 to 2/10 mm (more toward 2/10 than 1/10)

The cauls are now clearly free in the mortise

The cloth thickened 1/10 to 1/20 mm (difficult to measure even with adequate tool)

My first guess is that as the cloth seem to thicken the same as the wood, but the cloth is find twice on the keys, the mortises should have a similar fit under high moisture than low moisture.

But on my samples the mortise with cloth is more large, anyway.

Now I will dry (slowly) the 2 keys and the cloth. trying to have some control on the moisture

I use a professional HR thermometer with external sensor that can be inserted in the sealed bag

To dry the keys I will use a sillicate bag.

New measures tomorrow...

No. White/yellow "Titebond Original Wood Glue" is the original Titebond. Titebond is a polyvinyl acetate emulsion. It is nothing at all like hide glue.

What is marketed as Liquid Hide Glue is an actual hide glue with either urea or some other combination of chemicals added to retard the gel and/or curing rate and keep it liquid at room temperatures.

I know of only two such products currently marketed in the U.S.: Franklin Liquid Hide Glue and "Old Brown Glue" formulated by Antique Finishers, Inc. <http://www.oldbrownglue.com/>
Their working characteristics are similar but not identical.

A review of each can be found at:
<http://www.popularwoodworking.com/article/hide-glue-in-liquid-form>

ddf

Just for clarification, the article says Titebond Liquid Hide Glue is made by Franklin International. Titebond is a business unit of Franklin International.

True. But Titebond Original Wood Glue (generically known as PVA) and Titebond Liquid Hide Glue are still significantly different adhesives using completely different of chemistry and are intended for very different uses.

ddf