"At some point, it would be nice if some people who rebuild and replace
pinblocks would treat old loose holes with CA in various ways, and then
cut the old block apart once they have removed it, to see what really
DOES happen to the glue once we apply it. The theory of gluing cracks,
etc., is very pleasing, but until some people do some experiments which
allow direct observations it remains just a theory."
Susan,
I've done just that to bridge pins... pinblock experiment is on my list.
May as well share my overall results now. I'm falling asleep so I can't
pull up pictures now.
For a while I have suspected that thin CA glue doesn't pour down a
straight path as I try to secure a slightly loose bridge pin that is
causing false beats. I took an old bridge I salvaged for experiments and
applied CA glue to bridge pins with visual cracks, then I removed the
bridge pins and cut them in half with my 3/8" band saw. I was amazed at
what I saw... so much so that I repeated the experiment with CA tinted
with red die to make sure I understood what was going on. Right when I
got some good samples, my tire broke and my sample production ceased.
St. Louis was upon me so I stopped applying and cutting.
Without enough pictures to support my statement, here's what I found
that happens when I applied CA glue to a bridge pin removed from a piano
that had visible cracks beside it.
1. Bridge pin that moved easily when I pushed it with my fingernail: CA
glue wicked all the way down to the bottom of the hole.
2. Bridge pin that barely moved when I pushed it with my fingernail: CA
glue wicked down half way or so, maybe 5mm.
3. Bridge pin that didn't move at all when I push it with my fingernail:
CA glue wicked down a few millimeters.
4. Bridge pin didn't move at all when I pushed it with my fingernail:
This time I used CA glue tinted red, and my cutaway samples showed red
far, far away from the bridge pin hole. It looked like it immediately
wicked along small cracks deep into the bridge. I didn't see any red
along the bridge pin hole, but there was plenty in other places.
5. Summary:
a. It appears that that thin CA will immediately use capillary action to
trace micro cracks in the wood.
b. If the bridge pin is severly loose, it chases it down the bridge pin
hole as far as it can go.
c. If the bridge pin doesn't seem to be loose at all, thin CA glue
applied to the base of the bridge pin tends to wick throughout micro
cracks in the bridge.
Sorry I don't have pictures of red CA. I looked for them in the middle
of this post to no avail.
I would like to the see results of others' experiments of cut away pin
blocks as well.
John Parham
Original Message------
Hi, Thomas
For CA I prefer the Loctite brand, the small bottle with the long slender spout, but for 5 minute epoxy I don't prefer a particular brand. I think that the two squeeze tubes (like toothpaste tubes) are a little bit more convenient than the "double syringe" style, but I've used both. Best to get a small amount instead of big cans full of the two parts, so it doesn't go bad before you use it.
By the way, a couple of years ago I fixed a nearly fatally abused broken key from a Steinway M, which I had to take right down to shards and rebuild with proper geometry. I practically bathed in five minute epoxy for several days. The key turned out fine! But I got sensitized to five minute epoxy, which never used to bother me. First it felt like a sunburn, then very rough skin, finally my whole face was very red and swollen. It took several days to get over it. I've used epoxy a lot less often since. It might be a good idea to open a window, put on a fan, and use those light rubber gloves. I never thought I needed to ... attaching some photos of the adventure, if I can find them in my files. Someone else had mended the broken key very poorly, so that the tail was 1/3" lower than the front, and the balance rail hole was broken out.
The extra eighth of an inch might matter a little bit, but I think that the epoxy, used to make the hole smaller, would do the heavy lifting. I doubt I'd buy a whole set of the 2.5" pins just to get those two, unless you decide you'd like to have them in stock for another job. As someone else pointed out, an alternative method might be to block the bottom of the tuning pin hole, fill with epoxy, and then drill, but I think I'd try just swabbing the holes first.
There are also some little brass tubes from the supply houses which can be used as shims, but I think I'd stay away from them. I've had too much experience (in pre-CA days) of using an oversized pin or shimming a hole, having the offending pin tight as anything, but all the tuning pins in the immediate region much looser because the big pin spread cracks.
The thing about the water thin CA is that it follows cracks, so it theoretically will glue cracks and delaminations back together. Sometimes the first application doesn't "work", but I think it possibly might be because the CA has followed so many cracks so far that little is left at the tuning pin hole. Then a second application might work better, since the escape routes have been sealed.
At some point, it would be nice if some people who rebuild and replace pinblocks would treat old loose holes with CA in various ways, and then cut the old block apart once they have removed it, to see what really DOES happen to the glue once we apply it. The theory of gluing cracks, etc., is very pleasing, but until some people do some experiments which allow direct observations it remains just a theory.
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Susan Kline
Philomath, Oregon
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