Terry,
I don't know anything about bridge building, but
it seems to me that if you fill the saw kerfs with
West's mixed with their colloidal silica, you run the
risk of creating a somewhat vibration absorbing,
rather than transmitting, bridge root. And, at the dog
leg: a place where transmission might be needed most.
I would recommemnd the steam pre-bending method,
or just dry heat (heat gun?). Wood bends very nicely
with dry heat, sometimes.
But if you do the saw kerf thing, I'd try using
West's straight, with no silica, for higher density.
Just a thought.
BTW---My hat is certainly off to you as, perhaps,
the most recent victim of the piano rebuilding
affliction to ever attempt such extensive repairs!
Best Wishes,
Thump
--- Farrell <mfarrel2@tampabay.rr.com> wrote:
> Ron O. asked:
>
> "What did you end up doing at the bridge dog legs? I
> read the posts you received. Did you steam and press
> the vertical laminates before the final glue-up?
> Wolfenden suggested this technique with regard to
> bending the rims also."
>
> My first attempt was with Tightbond. I found that I
> applied so much clamping pressure that I distorted
> the bridge (distort is really a very mild term to
> describe the result of this excercise). I have been
> using small pieces of wood along the bridge at each
> clamp to spread out the clamping pressure. I did not
> use the one big caul method that Ron N. provided a
> picture of. I don't understand how you can be
> assured of getting proper clamping pressure at all
> locations. And it seemed like a lot of work to make
> a caul for each bridge.
>
> So, try number two. Well, first of all I think that
> I simply was trying to put too much bend into a 32
> mm thick pile of maple. Never the less, I tried
> Del's recommendation of notching part way through
> each lamination at the hard bends with a saw. After
> seeing how much wood I removed with the saw, I
> immediately thought of the wondrous gap filling
> properties of epoxy. So I wet all the pieces down
> with unthickened West System epoxy, and filled the
> saw cuts with a thick mixture of their High Density
> Filler, assembled and gently clamped to cauls. Just
> enough clamp pressure to get things into position at
> most locations, and a lot of clamp pressure at the
> dogleg. Several laminations still cracked - but no
> big deal with all the epoxy in there (fortunately
> the panel covers the bottom of the bridge root and
> the cap covers the top - this bend area is rather
> unsightly). With the light clamp pressure
> (everywhere but the dogleg), I ended up with
> perfectly smooth big bends in the bridge - !
> as desired. My dogleg ended up only 1 or 2 mm short
> of the bend I was shooting for - it just got
> smoothed out a little. There should be more than
> ample room to just have the section-end bridge pins
> ride a little high and low there - should work fine.
>
> I bought a big roll of 6 mil plastic from Home Depot
> (fairly thick stuff). Cut a piece a foot longer than
> the bridge and maybe six or eight inches wide.
> Arranged epoxied laminates on this long narrow piece
> of plastic. Pull up edges of plastic over sides of
> bridge and let flop over top. At this stage I could
> take off my gloves and handle my
> maple-laminate-filled burrito with extra slow
> setting epoxy sauce with bare hands. The plastic
> keeps the epoxy off everything - clamps, cauls, you,
> etc., and keeps in on the bridge laminates - kinda
> makes a neat little trough that is filled with
> epoxy. The bridge literally sits in a bath of epoxy
> while the epoxy cures.
>
> I may try steaming next time. Maybe not. The thing
> with steaming would be the wait for the maple to
> dry. Now how long is it going to take to dry with
> clamps and cauls and everything covering the sides.
> I suppose you could have the top and bottom exposed
> to the air. I guess I'd have to take some and figure
> its moisture content, steam it, and then monitor its
> weight to determine the moisture content to see how
> long it takes to dry. Or maybe you need to steam
> that thing, clamp it into the desired shape, and
> have a little heat source below and just toast it
> for a while. Still though, how long?
>
> Terry Farrell
>
> ----- Original Message -----
> From: "Ron Overs" <sec@overspianos.com.au>
> To: "Pianotech" <pianotech@ptg.org>
> Sent: Friday, March 14, 2003 6:48 PM
> Subject: Re: Bridge Cap Thickness
>
>
> > >At 6:20 PM -0500 14/3/03, Farrell wrote:
> > >What are the guidelines on how thick a bridge cap
> should be? And
> > >why. I've got a new vertically laminated long
> bridge that can be
> > >trimmed down to any height, and I'm trying to
> figure out how thick
> > >to make the cap. The cap will be horizontally
> laminated with about
> > >1.6 mm laminations. Laminations will be epoxied
> together. The
> > >installation should allow the cap to remain at
> near full thickness.
> > >It's a bit of a pain making the laminated cap,
> and that process is
> > >only complicated by increasing the number of
> laminations. I have
> > >five laminations now and it adds up to about 8 mm
> thick. I would
> > >like to not make it any thicker than optimal, or
> to the point of
> > >diminishing returns.
> > >
> > >Terry Farrell
> >
> > Terry,
> >
> > 8 mm of cap thickness will be more than adequate.
> The greatest stress
> > on the bridge cap wood will be at very top surface
> of the cap,
> > diminishing further down into the cap. We are
> currently building our
> > caps 6 mm thick using 6 x 1mm thick laminations.
> >
> > Good on you for getting stuck in at the deep end -
> all the best. What
> > did you end up doing at the bridge dog legs? I
> read the posts you
> > received. Did you steam and press the vertical
> laminates before the
> > final glue-up? Wolfenden suggested this technique
> with regard to
> > bending the rims also.
> >
> > Ron O.
> > --
> > _______________________
> >
> > OVERS PIANOS - SYDNEY
> > Grand Piano Manufacturers
> >
> > Web: http://overspianos.com.au
> > mailto:info@overspianos.com.au
> > _______________________
> > _______________________________________________
> > pianotech list info:
> https://www.moypiano.com/resources/#archives
> _______________________________________________
> pianotech list info:
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