Hardening Bridge Caps

[Ron Overs]

David, Dale, Dell and all,

I also agree with the practice of coating the top of the bridge. One 
of the reasons why multi-laminated bridge caps are so effective is 
that the laminates are permeated with glue during the gluing process. 
Any minor checks in the laminates, which can occur if they are dried 
too fast at any time from tree to product, are simply glued up to 
eliminate the risk of splitting. But the top surface of the top 
laminate will not be permeated fully with glue unless it is also 
deliberately coated on the top surface.

After finding that the top laminate can occasionally develop small 
checks after the bridge is pinned unless the top layer of the top 
laminated is also coated with glue, we have been manufacturing our 
laminated bridge caps by applying a layer of glue over the top 
laminate also. The plastic sheet which is placed underneath and over 
the top of the entire cap before the vacuum press diaphragm is placed 
in position prevents glue from getting all over the diaphragm. When 
the cap comes off the press both the top and bottom surfaces are 
sanded prior to fitting to a bridge. Caps laminated in this fashion 
are essentially a matrix of West system and maple.

In your case David, it might be worth considering making your own 
multi-laminated caps. It would save you the detailed clean up of the 
pin holes before pinning. We don't make our own laminates these days, 
since quarter cut 0.5 mm thick Rock Maple veneer can be purchased 
locally. We use seven layers for each cap to make up 3.5 mm, just 
enough thickness to accommodate the notching depth. The thinner 
veneer layers also allow for a more complete permeation of glue, 
which I prefer.

Below is an image-link showing the treble end of the bridge from our 
most recent piano, no. 7. The notching extends down into the seventh 
laminate.
http://members.optuszoo.com.au/ronovers/oversno7.2.jpg

Ron O.

>When cutting a new bridge cap I typically paint on a low viscosity epoxy to
>both harden and seal the cap.  I do this after drilling and notching but
>before pinning, sanding back the bridge top flat again before inserting the
>bridge pins. 
>
>I'm considering doing this same process with a thin CA glue which seems like
>it will offer some advantages: cures faster, wicks into the wood better,
>requires less sanding afterward. 
>
>Any thoughts on the differences in terms of providing a seal and adding
>density to the wood between the two substances?
>
>David Love
>davidlovepianos at comcast.net
>www.davidlovepianos.com


-- 
OVERS PIANOS - SYDNEY
    Grand Piano Manufacturers
_______________________

Web http://overspianos.com.au
mailto:ron at overspianos.com.au
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