With keytops do you really want a glue joint that is stronger than the wood?
I don't think so. When those tops come off I don't want any wood coming
with it. For this purpose that level of strength is overkill.
David Love
www.davidlovepianos.com
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Mike Morvan
Sent: Sunday, January 03, 2010 10:37 AM
To: pianotech
Subject: [pianotech] glues and clamping
List,
These topics have certainly generated some lively discussion. Back to
the clamp or no clamp discussion/theory, I feel the need to go over a few
things, more specifically some results we have found.
1. The glue we now use (our mineral plastic glue) requires clamping as does
almost every other glue. If ever in doubt, go back to basics. Disregard the
fact that you're working on an instrument and truly look at what you are
doing. With keytops, it is most likely some type of woodworking similar to
making a glue joint such as edge gluing, end gluing or face gluing. There is
some different criterion for all of them, and different glues required.
There is no "Silver Bullet Glue" or "Silver Bullet Process" that does it
all. Pianos are a complex blend of many materials and processes and their
assembly and maintenance crosses over into many different professions.
2. If someone can get a keytop off without pulling some of the wood off with
it, than something in the keytop replacement process has failed. Check your
glue, perhaps the wrong type, expired, suboptimal climatic gluing
conditions, clamping pressure either too much or too little, and both mating
surfaces need to be clean, flat, square and smooth.
3. Most glues, will develop a glue line that is stronger than the wood
itself; but again, to achieve this, well you know, the clamping thing again.
Some could argue the "rubbed" glue joint works well and it does, but I've
only seen it done with success and without inviting speculation in edge
gluing, not face gluing as is the orientation with keytops.
4. When we joyfully found the mineral plastic and it's proper glue over 2
years ago I was using pvc-e glue and was skeptical to use the mineral
plastic glue, especially since it cost more compared to pvc-e, and when we
get comfortable with something it can be difficult to change. I'm cheap to,
but will spend willingly for something I feel is better. I was happy with
pvc-e and was reluctant to switch. But when I did the clamping tests and
found the mineral plastic glue to be somewhat stronger than pvc-e (the exact
percentage I don't know), with the added benefits of being more viscous, and
drying nearly white, these properties sealed the deal. I tossed the pvc-e
out (it was probably expired anyway). Consider the viscosity benefit alone.
Inevitably when the tops are cut off a few unwanted chip-out or blow-outs
can happen on some keys and is unavoidable, the thicker glue fills these and
makes them less noticeable.
5. There is no money for me in selling the glue. It is expensive, I have to
buy it in 5 gallon pails and ship it here from Germany. Plus, it is an
"exotic" glue and has a shelf life of 6 months the has to be tossed. How
many gallons of glue does one use in 6 months? I'm simply posting unbiased
results that I have found. I love it when I find a better cutter or make a
better jig, things can always get better.
6. I admit that I did a couple (literally 2) sets of tops with contact
cement. One was with the solvent based formula and one was the water based
formula. The elimination of the clamping process was a dream come true, it
shaved 2-2 1/2 hours off the job; but I could not tolerate the smell and
could not figure out how to apply pressure evenly to the top and front at
the same time, which in theory, I thought needed to be done. Ultimately what
made me throw the contact cement away was the fact that the keytops we were
getting in to recover were previously covered with contact cement and
literally peeled off with no effort and no apparent bond strength. I have to
admit, I did not research why this happened, and do not suggest it will
always happen or ever happen again. Then there was the mentor factor, the
three people I was working with at the time, said stay away from contact
cement and always use hide glue for felt, leather, cloth and veneer, no
acceptions. Again, everyone has an opinion.
7. In the beginning, we must have done a half dozen sets of keytops with
pvc-e and no clamps; I used tape, elastics and gravity as have all been
described and suggested. Then, I did some testing on spare keys and found
that they were hard to pull off, and would not come off under normal
conditions. When purposely pulling them off (an abnormal condition), I noted
little if any wood came off with the top. Finally I made some custom clamps,
clamped the tops on and found that more wood came off of the top of the
keystick after clamping than without clamping.
In conclusion, I can't see a keytop coming off under "normal conditions",
whether using pvc-e, mineral plastic glue, or contact cement either clamped
or not clamped. I personally find that clamping produces a stronger bond,
and glues are meant to be clamped to achieve full potential strength (read
the bottle), but admit it; some may not think clamping is needed under
normal conditions. It's a matter of opinion. I do however feel that clamping
is a good habit to get into. A few percent better is still better. Type of
glue is a personal preference, they all possess enough potential strength
for the job.
When new keyboards are made, the tops are always clamped in some fashion.
Think about it, how many manufacturers will spend one penny or exert an
ounce of effort if it is not absolutely necessary. They certainly have more
R&D dollars than us "small fish" and they clamp. What has changed from when
the keyboard was made to when the replacement tops are put on? It's still a
plastic top; it's still a wooden surface. Again, back to basics.
It's nice to see the topic moving on to the more complex and difficult task
of getting the keystick tops cut square and parallel. The variables are
many and just when you think you solved the problem a keyboard will come in
and ruin your day; and when one has solved the "tops" problems, there is the
"fronts" problems to look forward to. They present an even trickier and more
complex set of circumstances. This is fun stuff.
My colleagues tell me to not get involved in these speculative irresolvable
issues, I think I'm going to take their advice for the future.
Good luck, Mike
BLACKSTONE VALLEY PIANO
Michael A. Morvan
76 Sutton Street
Uxbridge, Ma 01569
(508) 278-9762
<http://www.pianoandorgankeys.com/> www.pianoandorgankeys.com
mike at pianoandorgankeys.com
www.thepianorebuilders.com <http://www.thepianorebuilders.com/>
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