Crown without soundboards

[Peter KESTENS]

Ron,

Thanks for your reply.   It isn't that difficult to understand.  I hope for
you (and me) other techs would send a reply.
PEter


't MUZIEKINSTRUMENTENATELIER
PETER KESTENS
BELGIUM
KESTENS.P@DEBCOM.BE
-----Oorspronkelijk bericht-----
Van: Ron Nossaman <nossaman@SOUTHWIND.NET>
Aan: pianotech@ptg.org <pianotech@ptg.org>
Datum: vrijdag 2 januari 1998 22:34
Onderwerp: Re: Crown without soundboards


>Hi Peter,
>
>I was planning to post just this question to the list to see what other
>folks were doing. I haven't installed a board for a over two years, and,
>since I have a couple coming up soon, I was thinking of possibly updating
my
>jigs and methods if anyone had better ideas they would share. This is a
>great excuse to prospect for improvements. Here is what I have done in the
past.
>
>My current rib crowning jig consists of a nominally 1" thick board (junked
>upright front panel lumber) with one edge machined to a concave curve
>(somewhere in the ragged vicinity of a 60' radius). It is screwed to
another
>board (on one side) with straight edges and has a series of screw down
>clamps on the other side making a sort of stacked sandwich with straight
>base, rib caul in the middle, and clamps on top. I set my rib blank in the
>jig on it's side and bow it back into the curve with temporary clamps. Then
>I tighten the jig clamps to hold the bow in the rib, and remove the
>temporaries. I adjust the rip fence of the table saw to produce the rib
>depth I want, and rip the top off the rib (rib is laying on it's side in
the
>jig) with the saw. When the clamps are loosened, the rib springs back
>straight and has a nice square saw cut gluing surface with a uniform crown.
>The jig is ugly as home made sin, looks like a committee project, and is a
>bit cumbersome, but it's worked pretty well for me.
>When the assembled soundboard re hydrates, the crown increases somewhat (I
>can't say I ever troubled to find out to what degree), but settles in all
>right under string load.
>
>I hope the crude description makes sense. Now let's fish for some
>suggestions on how I OUGHT to be doing it.
>
>
>To the general populous:
>There is one thing that confuses me concerning what I've been reading and
>hearing about rib crowning. I hear more and more talk about putting the
high
>point of the crown along the bridge line. If the rib is machined to a
>section of a circle, this is not possible. The high point will always be in
>the center of the rib. You can put the center of load other than on the
>center of the rib by tapering the rib, thinning the panel, or both, but the
>high point doesn't move. Are the people who talk about doing this mistaken
>in their belief that they are doing something they are, indeed, not doing?
>Another obvious possibility is that they are machining a parabolic curve
>into the tops of the ribs instead of a radius and indexing the ribs into
the
>jig to get the tightest part of the curve where the bridge will fall. It
>also wouldn't surprise me a bit to find that the optimum curve (generally)
>is different for the treble than for the mid section, and different still
>for the low tenor. The 60' radius all the way through always sounded a
>little simplistic to me, but I don't have the qualifications to argue
>intelligently to the contrary. Not that such a consideration as that has
>stopped me in the past, you understand, but a guy has to aspire to SOME
>standards.
>
>
>Well, I've shown you mine. I'd love to hear all the gory details and
>suggestions anyone else out there has on rib crowning jigs, methods, curve
>forms, etc. Peter and I are listening attentively.
>
>
>At 05:18 PM 1/2/98 +0100, you wrote:
>>
>>'t MUZIEKINSTRUMENTENATELIER
>>PETER KESTENS
>>BELGIUM
>>KESTENS.P@DEBCOM.BE
>>
>>Ron,
>>
>>You mentinonned:
>>
>><A better way is to machine the top of the ribs to a crown, dry the panel
a
>>lot less severely than the first method, and glue it to the ribs.>
>>
>>Can you please tell me how much crown you give to the ribs and how you do
>this delicate job?  I always had in mind ribs had to be crowned in order to
>give crown to a soundboard but I can't figure it out how one can give with
a
>saw or a router this amount exactly to the ribs.
>>
>>Thanks a lot.
>>
>>Peter
>>
>>P.S.: happy new year.
>>
>
>May you learn quickly that the year is NO LONGER 1997 when you submit your
>January invoices. %-) Happy new year yourself.
>
> Ron Nossaman
>