[pianotech] Repairing bridge root lamination splits

[Ron Overs]

Hello Will,

That looks like Bubinga that they've used in the 
laminate that's split. I've seen this before on 
Steinway laminated bridges. Bubinga can be pretty 
cranky stuff, and I believe its less than ideal 
for making vertically laminated bridge stock. Is 
the grain direction out of alignment in the 
laminate that's failed? It usually is. The colour 
contrast might look very nice, but if it has a 
high propensity for failure why use it?

You could drive some west system epoxy into the 
cracks. Drilling a few suitably spaced holes 
along the line of the Bubinga laminate, which are 
sized to be a slight interference fit with maple 
hammer shanks, might be a good way to inject glue 
to the bottom of the cracks. Drill the holes to 
the depth of the cracks, fill the holes with 
epoxy and drive the hammer shanks home to the 
bottom of the holes. You'll in effect be filling 
the cracks from the bottom up. The bridge root 
will be slightly spread where the laminate has 
failed. It would be best not to clamp it up until 
after the dowels have been driven home. If the 
bridge is clamped together immediately after 
gluing, you'll get a good result.

If you've got a veneer trimmer you could set the 
fence along the convex side of the bridge to 
route out the Bubinga and replace it with 
something decent like Rock Maple. This might also 
be quicker than plugging, and it would remove the 
failed laminate, which will almost certainly be 
cross grained at the point of failure, from 
failing again at some later time.

Ron O

>To the list:
>
>Enclosed is a picture of the root of the treble bridge for the 1909 Steinway
>A2 in my shop that I am rebuilding.  I'm almost ready to glue on the bridge
>caps to the root.  As you can see in the picture, I have plugged the bridge
>pin holes with the small dowels that you get from Pianotek.  But you can
>also see that in the high treble on the backside, the laminations have split
>for about 5 or 6 unisons.  I am not satisfied that the plugs I inserted
>there are going to give the bridge and pins the integrity they need, so I am
>searching for a plan B to fill the offending space.
>
>My thought is to cut some plugs out of bridge stock and glue them in.  The
>idea would be to make the plugs slightly larger than the three pin holes,
>drill the holes, and epoxy them in. 
>
>Before I do that, I would be interested in the suggestions of others as to
>their go-to methodology.
>
>Will Truitt
>
>Attachment converted: Powerbk HD:DSC00168.JPG (JPEG/«IC») (00B999D8)


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