Making long bridges

[Farrell]

IMHO, the only way to get large dimension wood stable is to let it dry in a
climate controlled shop for a year or so. I've got about 50 bd-ft of nice
hard maple in my shop that was kiln dried, and then has sat in my 45% RH
shop for about a year. I just went out last week and picked up over 100
bd-ft of kiln-dried hard maple that I will let sit for a year or more in my
shop before I use it.

That's one nice thing about laminating. It is stable like a rock. One thing
about cutting a solid piece from large solid stock - even if the wood is
very dry, there can still be alot of internal stresses - when you cut out a
long piece to a pattern, you often find that after it is cut it will spring
or twist a bit one way or another. Laminating eliminates all that fuss.

Terry Farrell

----- Original Message ----- 
From: "David Love" <davidlovepianos@earthlink.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: Friday, March 19, 2004 12:33 AM
Subject: Re: Making long bridges


> Ron:
>
> As I ponder the laminated versus solid root choice, can you comment on the
> type of wood/grain angle/method of drying and preparing a solid root to
get
> it stable?
>
> Thanks.
>
> David Love
> davidlovepianos@earthlink.net
>
>
> > [Original Message]
> > From: Ron Nossaman <RNossaman@cox.net>
> > To: pianotech <pianotech@ptg.org>
> > Date: 3/17/2004 9:36:01 PM
> > Subject: Re: Making long bridges
> >
> >
> > >I need a crash course on bridge building (long bridges, bent laminated
> > >type).  Could use some suggestions on how I might go about getting
> > >information, how to make a template, what tools I might need,
materials,
> > >etc..  Whatever can be offered would be appreciated.
> > >
> > >David Love
> >
> > Hi David,
> > It's coming up on pumpkin time, and I'm about to collapse for the night,
> > but I'll try to do a quick outline for you.
> >
> > I use a rubbing (paper template) from the original configuration (before
> I
> > take the strings off) as a point of departure. After re-scaling, I use
> that
> > template to establish the new speaking lengths, which I use to lay out
> the
> > new bridge. Once you have the template for the new bridge, you need to
> > decide how you are going to build the bridge. You can cut it out from
> solid
> > stock, joined at the scale breaks to keep the grain running roughly
> > parallel to the bridge, or you can laminate it. You can laminate it
> > horizontally, putting the joints in each lamination in random places so
> the
> > strength of the assembly won't be compromised, which works fine. Or you
> can
> > laminate vertically, which means building a jig of some sort for
clamping
> > the laminations to the required curve. I've done bridges with continuous
> > vertical laminations, but it's a lot more work than should be necessary
> for
> > a one-off bridge. You need laminations at 2mm or under to make the
dogleg
> > bends at the struts to maintain a semi-log speaking length progression,
> and
> > a tremendous amount of clamp pressure.
> >
> > An easier way to do a vertically laminated bridge root is to use the
> > lamination thicknesses to supply the dogleg offset and not have all the
> > laminations continuous for the length of the bridge. Terry Ferrell asked
> > about this a while back, and it looked like a good idea to me, so I
tried
> > it. It works very well. Thanks Terry. You just have to build half a jig
> to
> > accommodate it, clamping the lamination stack against it without needing
> a
> > caul on the far side. Actually, I used backing strips to spread out
clamp
> > pressure, but still didn't have to cut out a full caul. Since the core
> > laminations don't have to be forced into an extreme bend, it's
> considerably
> > easier to manage and takes much less clamp pressure. It just takes a
> little
> > more pondering and planning before the fact.
> >
> > Cutting out a solid root and putting a cap on top is still easiest, but
I
> > like laminations. Just not all that bright, I suspect.
> >
> > That short stack of maple just above the bridge in the photo is the
> > laminated cap (1.5mm laminations), waiting to be cut and fitted to the
> > root. The bridge root is still rough cut here (hacked, actually), and
> will
> > be smoothed and contoured before the cap is installed.
> >
> > bridge laminations.jpg
> >
> > The laminations in this bridge vary from 2mm to maybe 5 or 6mm. I used
> what
> > I had lying around from previous projects that added up to the offsets I
> > needed for the doglegs. It's a tad over 30mm wide overall.
> >
> > To do this, you need a way to produce the required laminations - be it a
> > table saw or band saw, and (ideally) thickness planer. You need lots of
> > clamps (naturally), and scrap(able) lumber for building the jig. You
also
> > need a glue that is reasonably hard and creep resistant. I use Titebond.
> > Realistically the glue used for laminating doesn't need to be able to
> hold
> > continents together without shifting under billions of PSI. Gluing the
> cap
> > on top, and the panel on the bottom of the root laminates will
> effectively
> > insure that nothing is going to slide apart with a reasonably decent
glue.
> >
> > The rest is just the usual bridge work - or you can send me the original
> > rubbing and the offset revisions (or?) and we can work something out.
> >
> > Did I miss anything?
>
>
>
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