[pianotech] tightening the pressure bar

[Ron Nossaman]

On 7/29/2011 6:56 PM, Gene Nelson wrote:
> I am curious to hear your thoughts about tightening up the hold down
> screws on an upright pressure bar – pulling the bar down to put more
> pressure on the strings.
>
> That is; when do you decide to tighten and why – that is before you
> experiment – before you tighten and just see what happens?
>
> Working on a 40’s vintage Wurlitzer 42” console I found it sharp from
> the lo-tenor to the top and after 3 passes it still wanted to pull sharp
> (likely a separate issue).

Might well be related if the pressure bar friction is low enough.


> It has semi loose tuning pins – the type where you could feel every tick
> with the slightest movement of the tuning hammer and every tick produced
> a noticeable pitch change – it was not easy to set the pins.
>
> Thinking that tightening the pressure bar could add some drag/friction
> and help with this situation?

It might help at that, but there are potential complications. The 
danger, of course, is breaking screws. Restringing old uprights, I found 
that when I put the pressure bar back on, I could have a fair amount of 
tension on the strings and still turn the screws. Small increments, from 
one end of the bar to the other, and I could chase the bar down to where 
it originally was. The original position was obvious as the screws quit 
turning when the threads met virgin maple. I presume the screws in your 
Wurlitzer are already there, so driving them in farther becomes more 
difficult and chancy.

Also, some pianos have pressure bars bottomed out on plate mounds so the 
factory elves can't clamp the strings between the pressure bar and the 
plate. You might check that second.

The first thing to check is the approximate counter bearing angle. If 
it's already in the 15°+ range or so, lowering the bar probably won't 
help much. If it's in the 5°-10° range, it might.

If you decide on lowering the bar, and the screws resist turning in to 
the point you worry about breakage ( you may have to lower tension 
some), you can remove screws one at a time, check hole depth, and run a 
longer heated screw down deeper into the hole than the original to 
extend the threads. Put the original screw back in with a bit of soap or 
wax on the end, and do the next one. Then CA the tuning pins. The 
question is if the whole thing is worth the time and expense to learn if 
it will help. If you can get it paid for, it's a good educational 
experience, and you can enhance our education with a report afterward.  <G>

Ron N