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MMD > Archives > February 2000 > 2000.02.06 > 07Prev  Next


Pinblock Plugs & Repairs
By Jon Page

Pinblock plugs are a viable long-term repair.  You can get them in
either 3/8" or 1/2" diameter.

Don't drill all the holes out at once.  Alternate them.  Some holes
you may want to place the smaller plug where the pins are really close.
Cover the plugs with a cloth as you drive them in to avoid splatter.

Use a high grade epoxy, not the 5-minute variety.  West Systems is
a good line: their fillers and fairing compound allow you to mix an
adhesive to any desired consistency.  However, I prefer to use these
additives with epoxy from Epoxy Technology, Billerica, Mass., tel.
978-667-3805,  fax 781-272-1530

Their 301 is a water thin (really) material which is approved by NASA
for space flight programs.  It is use mostly for fiber optics but has
many other uses.  A 1-pound can is $36.75 ppd. (as of 2/99).

It is great for sound board cracks.  I wet the surfaces first with
it thin, then mix in filler, and wood flour or fairing compound for
coloring.  I tape the surface of the board and invert the piano to
inject the epoxy from the back/bottom.  Otherwise you would tape
between ribs and alongside the crack on the surface.

One problem with cracks is that the wood cells have suffered compres-
sion damage or dry rot.  Wood glue does not soak in like the water thin
epoxy does.

Last summer I repaired an old Bechstein grand where 15 years ago a
'tech' had plugged the block.  Unfortunately he did not attend to the
cracks in the block itself and the tension eventually cracked the block
further, aside from a sloppy job; the plugs were not holding.  Wrong
glue.

The block was mortised into the case.  The case and veneer were fragile
so I opted to make an inlay of pin block stock.  I drew out an outline
and made a pattern to rough cut the inlay.  A bench top drill press and
a Forstner bit removed the old pinblock material down to the bottom few
laminations leaving the sides to be cleaned up with a chisel.  The
inlay was dry fit nice and snug.

Being an exposed block I applied the face veneer and finished.  Then
mapped the holes, removed the inlay and drilled the pin holes on a
drill press.  301 was applied to wet the surfaces and then filler
added.  The next day, after it set up, I poured more epoxy into the
margins where it pulled in.  The plate flange to block mating was
reinforced with Marine-Tex.

I was quite pleased with the results.  This piano also necessitated
me to design a new tool for gluing the sound board back to the ribs
without the use of screws.  I have use them for gluing bridge caps
as well.  I have an image file if any one wishes to view the pressure
applicators.

I need to get a coffee...

Jon Page, piano technician
Harwich Port, Cape Cod, Mass.


(Message sent Sun 6 Feb 2000, 14:14:35 GMT, from time zone GMT-0500.)

Key Words in Subject:  Pinblock, Plugs, Repairs

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