[pianotech] Increasing bridge height

[Ron Nossaman]

Will Truitt wrote:
> Hi Ron:
> 
> I'm at home and not at the shop, so I'm trying to do this from memory.  I
> believe #21 is 193 mm. If you want the rest of the measures at the section
> ends, I'll get that tomorrow.
> 
> "I'm still trying to figure out where you plan to set the plate and bridge
> heights, and why. Are you planning on boring hammers to accommodate what's
> there without changing bridge or plate heights?"
> 
> Changing bridge heights is why I started this thread, and the whole point
> was to explore the ramifications of increasing the bridge height in targeted
> areas. I'm putting a new board in this piano, and wanted to explore this for
> the many reasons already discussed.  I have not fixed yet where it will end
> up, but it looks like I will raise the high treble end from 25 mm to 32 or
> 33 mm.  At note 21 the present bridge height is 33 mm. and I will likely
> make the bridge along its length fairly consistent in height.  I will not be
> using vertical hitch pins, however, so the finished bridge heights will have
> to accommodate targeted downbearing values as well as the curvature of the
> plate. I still have not yet pulled the plate as I have just begun teardown,
> so I have a lot more groundwork to lay before I know where my feet are. 
> 
> It's premature for me to try to get into the whys and how much, as I am
> still learning as much as I can before proceeding (and I have learned a
> great deal from all of you so far, THANK YOU VERY MUCH!)

But the whys and how much are exactly what you need to 
determine before you start cutting wood.


> Whatever values I end up with on the finished bridge, I will still likely
> end up tapering the bore, The bore will be derived from the measured string
> heights of the strung piano after all modifications.  The taper could at
> least be partially mitigated if I end up tilting the plate down in the bass
> and up in the treble to help level the string plane out (as Jude has
> suggested). I will likely be changing both plate and bridge heights, so
> obviously the original string heights serve only as a starting point and
> frame of reference. 

Have you determined what you'll end up with in string height? 
If you raise the treble end of the plate to accommodate a 7mm 
bridge height change, you'll end up with something like a 3mm 
or less change throughout the string height for the long 
bridge, with about a millimeter difference from #21 and #88.


> I don't know if it matters if the bore is a tad shorter or longer.  What
> qualifies as a "tad"?  Does 6.5 mm. difference within the treble string
> plane qualify as a tad?

Where's that 6.5mm difference after you raise the treble end 
of the plate? That's my point. You are, or you aren't raising 
the bridge height and plate there. If you aren't, you deal 
with that height difference. If you are, you won't. Figuring 
the hammer bore as if you weren't changing bridge and plate 
height doesn't much reflect what it will be when you do, does 
it? Do it or don't do it, but but work with the appropriate 
set of figures either way. In this case, a tad is in the 
middle of the 3mm or so variation between #21 and #88, which 
would be around 1.5mm. I personally don't find it necessary to 
waste time tapering the bore for that little difference. If 
you do, go for it.


> "Play better".  I can't speak for Bruce Clark, and it would not be fair to
> attribute this to him verbatim as what I quoted is my second hand recounting
> in my class notes.  I think it would be best to leave the explanation of
> that to him at another time.  

Best left unsaid then, until it can be backed up with 
something rational.
Ron N