Which begs the question: what will loosen the glue joint of PVC-E? Hot hide with ivory was heat and steam. David Ilvedson, RPT Pacifica, CA 94044 ----- Original message ---------------------------------------- From: "David Love" <davidlovepianos at comcast.net> To: pianotech at ptg.org Received: 1/3/2010 2:00:41 PM Subject: Re: [pianotech] glues and clamping >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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