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<DIV><FONT face=Arial size=2>Hello Folks!</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2> David Hughes, RPT, =
signing in
here. Dale Erwin, RPT, was kind enough to forward some PTG =
Tech-Chat to me
this morning which apparently took place yesterday regarding =
pre-stressing of
soundboards during bearing setting. My name was mentioned so I thought =
I'd chime
in.</FONT></DIV>
<DIV><FONT face=Arial size=2> First of all, I must =
apologize
for not partaking regularly of the PTG tech chat room (or whatever I =
should call
it). I used to subscribe several years ago, but at the ripe old age of =
46 I've
decided I've got to leave the pianos in the shop from 5:00pm until 8:30 =
the next
morning. I'm not sure of etiquette here - I hope my comments will be
accepted/welcomed. Furthermore I'd like to add that I'm astonished and =
flattered
that I was even mentioned in your discussions. The fact that you know =
who I am
is noteworthy to me, and that some even listen to my ramblings at PTG
conventions is even more pleasurable. Okay, enough mushy talk, I'll put =
the
Kleenex away. Back to the chat thing, I'm never quite sure who is =
contributing
what in this format, so if I'm not crediting someone correctly, please =
forgive
me.</FONT></DIV>
<DIV><FONT face=Arial size=2> I believe it was =
Terry Farrell
who quite accurately described our method of loading the board. As was =
alluded
to, before you decide if/how you are going to do this, you've got to =
know how
your soundboard is built. Is it a compression crowned panel? Are the =
ribs
pre-crowned? What are the ribs made of? How thick is the board? How is =
it
tapered? And on and on. All of this is a little more than I care to =
delve into
tonight, so let's get back to the loading thing.</FONT></DIV>
<DIV><FONT face=Arial size=2> With our pre-crowned =
eastern
white spruce ribbed soundboard (except that the first 3 ribs in the high =
treble
are Sitka), we wedge the middle of the board down 3mm using the plate =
strut
which passes over the board at about note 40 on most Steinways. This is =
done
with the plate suspended on the nosebolts with the cap nuts fastened =
down, and
the plate is also simultaneously, temporarily screwed down to the new =
pinblock.
This hovers the plate, fixed, at its ultimate resting place. No acoustic =
dowels
in yet? Don't sweat it - not needed. I use a long screwdriver as a pry =
bar and
force the board down using this central strut as a fulcrum point and =
shove a
wooden wedge in there. Real hi-tech. So, if the unloaded "free air" =
between the
top of the new raw bridge and the underside of this strut is, for =
example, 10mm,
I wail on that puppy until I get 13mm and shove the wedge in to hold. =
Rocket
science accomplished. Our boards are quite stiff. This takes some muscle =
- no
broken plate struts yet :-). </FONT></DIV>
<DIV><FONT face=Arial size=2> </FONT><FONT =
face=Arial
size=2> Let's talk about a model A-2, just as an
example: for the plate strut at note 40: 3mm; the plate strut at =
51/52
break: 2mm; the plate strut at the 68/69 break: 1.5mm, or some visible =
movement.
Let's face it, if you push this down 3mm up there, you'll be picking up =
kindling
off the floor....... and you'd need a hydraulic jack to do it in the =
first
place. Terry states very wisely that pushing the board down using the =
plate
strut at note 20 (actually about note 25 on this scale) is risky =
business. Why?
The plate is flexy back there and you'll do more bending upward of the =
plate
than shoving down of the soundboard. But you do have to do =
<EM>something</EM> to
assure the board is captured. Make sure the plate does not rise and =
deflect the
board a gentle 1.5mm, tops. For me, this is the area of the board I've =
striven
to keep "free". </FONT></DIV>
<DIV><FONT face=Arial size=2> Likewise with the =
bass bridge.
The soundboard (correction: <STRONG><EM>our </EM></STRONG>soundboard as
<STRONG><EM>we</EM></STRONG> build it in <STRONG><EM>our =
</EM></STRONG>shop,
which in no way infers <STRONG><EM>this </EM></STRONG>is the way to do =
things)
"sees" the bass strings as big, albeit pretty, earthworms. They =
have more
than enough mass to couple adequately to the soundboard given the right =
bridge
pinning, etc. So why would we (correction: why would I) want/need to =
establish
any bearing there? I want the board to be as flaccid as possible =
back
there. Downbearing is only going to foul this up. The amount of =
long-term sag in
the soundboard we construct, especially in this area, is so minimal, =
truly no
"downbearing" is desired. So, when the bass bridge is cut for bearing, I =
look
for the string to virtually touch the top of the bridge at the same =
instant it
contacts the hitch area. Maybe a beam of light could fit in there,
maybe.</FONT></DIV>
<DIV><FONT face=Arial size=2> Now that we've got =
the board
screaming in a squashed condition (how'd you like to live the rest of =
your life
like that poor guy?), I set 0 bearing at note 20, a dime at note 40, a =
nickel at
note 51 through note 69, and about a nickel up to note 88. The backscale =
lengths
are a determining factor here. And forget trying to get it right on a =
model S in
the high treble: the plate casting elevations are all wrong up there =
relative to
the elevation of the crappo disastro bar. If you get the highest handful =
of
notes to actually say something interesting on an S, you've done a fine
job.</FONT></DIV>
<DIV><FONT face=Arial size=2> This much pressure =
always alarms
people. For the third time I offer that this system works for our =
soundboards,
which are high impeadance, stiff darned things. I've got about 100 belly =
jobs
out there over an eleven year span and I haven't eaten a job yet...... =
and the
pianos sing...... and the rims haven't pushed out 1/4". Of course, =
if we
were the Beatles, it would be our bird that would be doing the singing,
right?</FONT></DIV>
<DIV><FONT face=Arial size=2> And David Love is =
right: I don't
sweat it too much beyond this. And as far as I'm concerned, Terry's head =
is
screwed on just fine.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2> Dave Hughes, =
RPT</FONT></DIV>
<DIV><FONT face=Arial size=2> ps: Would someone =
kindly forward
this to David Love? I don't have his e-mail address.
Thanks.</FONT></DIV></BODY></HTML>