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 >
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