[pianotech] glues and clamping

[chip tuthill]

Hi Chuck,

I used 100's of gallons of contact cement in my wood shop back in CT. I hated making counter tops, but work is work. We sprayed the horizontal surfaces. Most edge banding was done on an Olympic EB-4. It was a hot melt 4 station edge bander. It applied the adhesive, trimmed leading & trailing ends, and had two top and bottom trim stations. For hand applied edge banding we ALWAYS used two coats of adhesive. The first coat would seal the substrate edge. The second provided the bond. On small parts, we would coat the horizontal surfaces two times also. Some applicators will not wait until the surface is completely dry. They attempt to use the wet surface(s) to allow for final positioning. These are mistakes and will result in a poor bond. Hand rollers provided enough pressure to ensure a good bond. Your advice below is spot on.

We never had glue failures- that got outside the shop. It is possible to remove the laminate with an adhesive solvent. It is messy and does not leave a clean surface.

Chip



________________________________
From: Chuck Behm <behmpiano at gmail.com>
To: pianotech at ptg.org
Sent: Sun, January 3, 2010 9:04:43 PM
Subject: Re: [pianotech] glues and clamping



>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. Mike Morvan<

Mike - This is what happens when either only one application of cement is given to the keystick, or no clamping pressure is applied after the surfaces are brought together. The "multiple applications may be required on porous surfaces" caution given on the label needs to be heeded. The first coat is pretty much absorbed by the wood. The second coat provides the bond strength. Plus, pressure needs to be applied to the keytop, in my opinion, to seal the deal. I do it with a wood vise with a cork face cranked down hard enough to leave an impression of the key in the cork. I only keep the pressure on until the next key is assembled, but it makes a huge difference. Before the key is put in the vise, I can still pry the keytop from the keystick. (If for example I absent mindedly have put a F keytop on a E keystick). After the 30 seconds or so in the vise, it's a no-go getting the surfaces apart without the use of a hot iron.  Using the proper techniques, the
 bond in my experience will last. Scanning down my data base, I count 15 pianos which I restored back in the 1970's which I still tune and maintained. None of these pianos has had any problem of any sort with the keytops which I installed. Thanks Mike, by the way, for all of your thoughtful comments. This being your area of expertise, your opinions on the matter are held in high regard. 

Having said that, I'm going to follow Mike's lead in bowing out of this discussion. This is not an argument which needs to made. For many procedures in piano repair, as long as a technician is
using proper techniques, satisfactory results may be obtained using a
variety of products and/or tools. The only point I wished to make in the first place in the case of gluing plastic keytops, is that contact cement,
properly used, works well. PCVE adhesive, taking all that has been said
about it into consideration, apparently works just as well. If you want to argue that, go
ahead. As for me, I say "uncle."  Respectfully yours, Chuck Behm 


      
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