This is a multi-part message in MIME format. ---------------------- multipart/alternative attachment ----- Original Message -----=20 From: Tony Caught=20 To: Pianotech=20 Sent: September 21, 2002 7:43 PM Subject: Re: hammer felt (Renner Blues) Dave, You wrote The importance of the staple is somewhat controversial. There are = those who argue that it adds tension to the lower part of the hammer and = those who say it doesn't make any difference. The Renner blue is, of = course, without a staple. =20 Not having a staple would mean that you cannot use this hammer in high = humidity conditions. However, As the hammer absorbs moisture from the air, the tension created = varies greatly as does the tone. Possibly being not stapled would allow = this increase of tension to spread more evenly over the hammer and not = be restricted by the staple. Tony Caught caute@optusnet.com.au Tony, et al., In general the staple is an insurance policy against a variety of gluing = problems. In the early days of piano building, of course, animal hide = glue was the only adhesive available to bond hammer felt to the wood = molding. Whatever its other merits, animal hide glue was (is) = particularly unsuited to this task--it goes on hot and, as the felt is = pressed against the wood molding, much of the water solvent migrates = into the wool felt. This leaves the glue too dry to form a reliable = bond. Something needed to be done to retard this water migration, hence the = various shoulder treatments that ultimately came to be called hammer = reinforcing or shoulder hardening solutions came into use. Despite their = names, none of these solutions did much to reinforce anything and they = were not intended to harden the working end of the hammer at all. They = were designed to retard the rate at which the water solvent component of = hide glue migrated into the felt and, hence, help prevent starving the = glue joint. A starved glue joint between the felt and the wood molding = results in a fairly weak bond and is susceptible to early = failure--especially under varying stress loads.=20 Like wood, wool felt expands and contracts with variations in moisture = content creating physical changes in the felt that do continuously vary = the stress loads on the felt-to-wood glue joint and that lead to its = rapid breakdown and failure. Under these conditions the staple does help = to stabilize things--enough, at least, to prevent most felt-to-wood = bonding failure.=20 Most of the adhesives used to bond hammer felt to the wood molding today = do not have this problem, or the problem can be controlled in other = ways.=20 One way is to raise the moisture content of the felt to the point at = which the water solvent in the glue is not so readily drawn into the = felt. An unfortunate side effect of this process is that when the hammer = felt is pressed into a heated caul--as is typical of nearly all hammer = makers today except for Isaacs and Ronsen (are there others?)--the felt = takes on a rather permanent set much like your wrinkled wool slacks do = when they are steam pressed at the cleaners. This pressing process = results in the much more dense and less resilient hammer that we all = know and love to voice.=20 Even today not all of the adhesives used to bond hammer felt to wood = moldings are completely waterproof after they are cured. For a variety = of reasons some hammermakers use one of several thermoplastic adhesives = similar to commercial PVAs (white glue) and/or aliphatic resins (yellow = glue). These adhesives are generally moisture resistant but can fail if = exposed to very high humidity levels. With these adhesives the reasons = for failure are different than those encountered with animal hide glues, = but the point of failure and the type of failure is the same. In these = hammers the staple is probably an essential structural component. If the = adhesive is rated as 100% water/moisture resistant--and if it is = properly handled and applied--the staple is not necessary for structural = purposes.=20 It is debatable as to whether the staple is desirable--or at all = effective--at promoting, enhancing or stabilizing tone. Generally the = staples are inserted below the parting line of the hammer caul and well = below the point at which the trimming knife has cut deeply into the = continuity of the outer layers of felt. Personally, I don't see how a = staple of any variety can do much to support the functioning portion of = the hammer from down there, though I'm willing to be convinced. (I will = say, though, that I've taken out enough hammer staples and have = tried--unsuccessfully--to hear any resulting tonal differences to be = some skeptical.) Nor do I see how staples of different types are going to function = differently, assuming each is installed correctly. Ron has described the = different types in one of his posts and I have found problems with each. = The two types of through staples are very often loose (especially the = T-types), obviously supporting nothing but themselves and hardly that. = The U-shaped staples are driven in with an air hammer and come in a = variety of lengths. These lengths must be carefully selected to extend = through the shoulder felt and into the wood molding. Many of these = staples are coated with a thermo-activated adhesive--the adhesive is = heated by friction as the staple is driven home--and once it enters the = wood molding some reasonable distance it is structurally and permanently = secure. It is desirable that the staple not extend all the way through = the molding. Now, look at the side of a hammer and consider how the = staple is inserted and you'll quickly see how tricky it can be to get = this just right. Being just a bit heavy or light with the trimming knife = or slightly high or low on the shoulder from your desired insertion = point can make quite a difference in how far the staple penetrates the = molding. As well, the staples only come in a limited variety of lengths. = Three or four lengths will be used on one set of hammers. Given some time I could probably think of a few more things to say about = hammer staples. But I suspect I've all ready tossed out enough stuff to = generally confuse things. Regards, Del ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/6a/cf/0d/dd/attachment.htm ---------------------- multipart/alternative attachment--
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