Lowell Component Downbearing Gauge

[John Delacour]

At 1:51 pm +0000 7/5/07, jimialeggio5 at comcast.net wrote:

>John,
>
>Your points are well taken...but here is my big question regarding 
>the whole  after-stringing downbearing measuring concept.

Before I go on, I think it is accepted that measuring the angular 
deflections after the stringing is no more than a checking of 
results.  As I said in my last paragraph, "although this method is 
quite accurate for measuring and demonstrating the angle after the 
event, it is not the perfect method for setting up the angles before 
the piano is strung"

>The innate inaccuracy from any of these techniques, given the 
>strings' speaking  length tendency to deflect and vibrate while your 
>fussing with whatever tool, will yield a measurement that needs to 
>be taken with a grain of salt.

Well, the purpose of my message was merely to point out the 
deficiency of a tool that resolves only to one tenth of a degree and 
to show that Dale Erwin's primitive method can achieve more than 
double the accuracy of the Wixey digital gauge.  Steel strings at 
pitch are not going to deflect to distort the measurement either 
under the weight of the Wixey gauge or under the light pressure of 
Dale's fingers and I can think of several far less reliable methods.

>   Add to that that since changes in the downbearing at this point 
>can be made locally with vertical hitch pins, but only globally 
>(moving the plate) with standard hitch pins...what does a very time 
>consuming very localized measurement buy you?

I am not familiar with vertical hitchpins, accujust pins etc., which 
are a peculiarly American development rarely encountered in Europe. 
Certainly the primary setting is achieved by accurate positioning of 
the hitchplate/metal frame but on most pianos the fine adjustment is 
made both globally and locally by shimming the string-rest, whether 
it be the standard cast-in type covered in bearing cloth or the 
'duplex' type.  Examination of high quality pianos from the good old 
days will show that adjustments as fine as a paper's thickness have 
been made.  Of bridge-planing I say nothing.

>If you are going to change the bearing you would most likely do it 
>globally( unless there are vertical hitchpins throughout) and that 
>change would be monitored empirically anyway, ie by ear. So my 
>thinking would be come up with a way to "get a reasonable sense" of 
>the static downbearing quickly and proceed with an informed, but ear 
>guided response. The big reason I see for being able to very 
>accurately measure after-stringing downbearing is to compare it to 
>the projected board deflection you predicted prior to setting 
>downbearing, to see it you are predicting the affect of string 
>loading reasonably accurately for future projects.

Well yes, except that to "proceed by ear" is not the way I would ever 
go, since the final aural effect is not going to be evident until the 
piano has been up to pitch for a couple of weeks.  I'd also say that 
the only way to make a proper observation is to take measurements as 
accurately as possible both before and after.  I imagine a situation 
where you use the Wixey gauge both before and after and by good 
fortune end up with a piano that sounds perfectly heavenly.  At that 
point you say to yourself, "Damn! I wish there were not a possible 
error of 0.2 degrees in my measurements."

Every restoration project will be different.  The source, the 
condition, the crowning, the age, the thickness etc. of every board 
will all affect the degree to which it will sink under a given load.

Since Lowell is in the title of this thread, it might interest some 
people to read another of his patents US Patent 1705153 
<http://tinyurl.com/yvsef3>.  The reason I am taking an interest in 
this thread is that I have a project under way which I want to be 
accurately repeatable, and am considering various test procedures.  I 
mention Lowell's patent simply as a starting-point for a downbearing 
simulator, since from a cursory reading I get the impression that 
something better could quite easily be devised, and I am sure great 
makers such as Kawai must have some fabulous device of the kind in 
their lab.

Of devices to measure and set deflection before stringing, more anon.

JD