View Only
  • 1.  cold versus warm pressed hammers

    Registered Piano Technician
    Posted 09-15-2014 13:43
    This message has been cross posted to the following Discussions: Hammers and Voicing .
    There has been lots of discussion over the years about the differences between hot- and cold-pressed hammers. Some manufacturers, including Renner and Abel, claim to do "warm"-pressing, but it has been difficult to nail down what that means. This summer, though, when I asked Norbert Abel about pressing temperature, he responded "40º" without hesitation. He said it was just to make the felt a little more flexible. 

    40ºC = 104ºF, or a hot summer day in Albuquerque (a mild one in Phoenix). I can't see that that degree of heat would have any deleterious effect on the wool fibers, or that in itself it would make any significant difference from "cold" pressing (which would be at the temperature of the room where the work was being done: does that mean 60º? 80º? Does it depend on the time of year?)

    This is borne out in my experience in voicing new Abel versus Ronsen Weickert special hammers (I put on a couple sets of each this summer). Needling felt about the same, and the results sounded essentially the same. I essentially use the procedure recommended by Renner: deep needles pressed into shoulders in a regular pattern, with the aim of increasing the tonal gradient. That's what I did, and the tonal gradient did, indeed, increase, become more gradual and higher at the top end, on both types of hammers.

    I suspect that in past years both Renner and Abel used more heat than that, but I don't know how to find out. The hammers seemed far denser and harder to get needles into, in any case, and it took a lot more insertions to get acceptable results.

    Fred Sturm
    University of New Mexico
    "When I smell a flower, I don't think about how it was cultivated. I like to listen to music the same way." -Federico Mompou

  • 2.  RE: cold versus warm pressed hammers

    Registered Piano Technician
    Posted 09-15-2014 17:24
    My last discussion with Ray Negron about this was that Ronsen is not a room temperature cold pressing.  There is the application of a small amount of heat (emphasis on small).  It don't recall the amount and it's slight but it's not room temperature.  I don't know how to find out about Renner and Abel either but certainly the pressings tend to be denser then the Ronsen product.  There are various factors that go into what comes out of the press.  Some that is the density of the sheet to begin with, how much pressure, how much heat and where the heat is applied (lower or upper cauls), how much heat is used with the inner caul (the caul that basically creases the sheet to begin with) and how long it's left in the press with the heat on.  Jack Brand mentioned to me at one point how much heat is required to alter the character of the fiber but I don't recall what it was.  Certainly higher than 40 degrees (C).   Heat alone won't tell you much about the final density of the product. 

    David Love RPT
    415 407 8320