[pianotech] glues and clamping

[Arthur Sacco]

  Hi Michael


  I give you A+ on your below response, I do like
  your last paragraph. I'm saving all of them for your next
  published book.
  See you tomorrow.
  Arturo
  From: Mike Morvan 
  To: pianotech 
  Sent: Sunday, January 03, 2010 1:37 PM
  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
  www.pianoandorgankeys.com
  mike at pianoandorgankeys.com
  www.thepianorebuilders.com

   



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