Pneumatic Press Bending

[Delwin D Fandrich]

----- Original Message -----
From: "Farrell" <mfarrel2@tampabay.rr.com>
To: <pianotech@ptg.org>
Sent: February 17, 2002 6:34 AM
Subject: Pneumatic Press Bending


> To those souls that delve into soundboard building with a pneumatic press:
>
> David Hughes runs 35 psi hose pressure in his press. Others have indicated
that they run 40 or 50 psi. Clair Davies indicates he runs 100 psi in his
cauls. Mr. Davies indicates that Steinway uses 100 psi (end of discussion,
right?). He cites the Bruce Hoadley book "Understanding Wood", which I
believe is generally a well respected resource. It reportedly indicates that
100 psi is a minimum pressure needed for a superior glue joint on softwoods.
Is there some justified thinking that suggests this guidance should not
apply to the rib-to-soundboard glue joint?



Terry,

I tested a bunch of different pressures with rib-to-soundboard joints a few
years back. Below about 30 lbs the failure was predominately glue failure
from thick glue joints. Above 70 lbs or so (I don't remember the exact
figures) the failure was primarily due to starved glue joints. The strongest
adhesive bonds resulted from pressures between about 40 lbs and 60 lbs where
the predominate failure was with the wood. We use between 40 and 45 lbs in
our press.

Del