Plate and Rim

[Delwin D Fandrich]

----- Original Message -----
From: "Phillip Ford" <fordpiano@earthlink.net>
To: <pianotech@ptg.org>
Sent: May 08, 2002 7:37 PM
Subject: Re: Plate and Rim


> >As I recall they are hardened 3/8" x 5" fully-threaded machine bolts.
>
>
> For the sake of discussion let's assume 3/8" bolts, fully threaded.  I'm
> not sure what the root diameter would be but to be on the safe side let's
> say 1/4".  Let's say the plate is suspended 1 inch above the rim.  Assume
> relatively low strength steel, say 60 ksi ultimate.

Some higher than that, I think. I don't remember the grade but it's up
there. And it really shouldn't be up there that high.


>
> By my quick calcs the
> amount of load to break this bolt in bending at the rim, due to an applied
> load at the plate, would be about 90 lbs applied at the plate.

Only 90 lbs? I think I'm going to start worrying....


>
> So, given
> that there are several bolts this is probably adequate.  Also, since root
> diameter is probably greater, material strength is probably greater, and
> the plate is perhaps closer to the rim, this number is probably
> low.  Still, it doesn't seem wildly overdesigned.  I might opt for a bit
> bigger bolt.  I don't really know how stiff a bolt you would need to be
for
> coupling the plate and rim so that the plate would resist rim
> movement.  This bolt size seems to be working on Baldwin pianos, so
perhaps
> it's big enough for that job.

I'm not sure you really need to -- or even can -- 'resist' rim movement.
Just keeping the two tracking together should do it.


> >
> >Hmm. I suspect that would depend on where and how the stiffness was
> >measured. With the plate screwed to the pinblock of any model Steinway
> >grand, for example, but free from the rim it will be much easier to twist
> >the tail of the plate than the tail of the rim. At least in the short
term.
> >Over a long period of time the rim might twist somewhat more, I suppose.
>
>
> I had been thinking of load applied in the string plane.  I think that the
> plate is significantly stiffer for load applied in that way than the rim
> is, which is why I don't think that much of the string load ends up being
> carried by the rim.

Agreed. Which brings us back to the beginning -- the plate mounting system
should be designed to hold and support the plate not some hypothetical
string load which never really does get into the act.


>
> Is the new grand getting close to release?

Soon, but not imminent.

Del