Vince Mrykalo wrote: >>Don, I know in the past there was a problem with hammer centers freezing up in YCh grands. In my experience, an application of protek was only a temporary fix. Has anybody figured out why this was happening? Do you have any information that would shed some light on the problem? I have found also that using the broaches and repinning, if the repinning was a little snug, working the part would loosen it up satisfactorily. But then I wonder if it would stay that way or again tighten up later. If you would like to respond to the group on this, go ahead. Thanks!<< Don Mannino's reply: I went to Korea in September 94 to finally work through this problem and help get it solved. Our action department had been making minor adjustments to procedures, and what was needed was a more major change. The bushings themselves were unstable. Although the bushings were sized correctly, the wool fibers were being compressed into position by wet sizing only, and the fibers didn't stay put under heavy use. The combination of heat and shocking of the felt caused the fibers to come back out of their squashed positions and tighten up against the pin again. The reaming / burnishing process disturbs the fibers sufficiently to leave them stable. I have heard of only one occurrence of our parts tightening up again after reaming, and the circumstances in that one case were not ideal (inexperienced technician, possible contamination of the cloth, etc). YC has a test chamber where the action can be pounded for a predetermined number of keystrokes while the temperature and humidity in the chamber are cycled up and down. During our work we ran actions for 200,000 keystrokes (about 2 days constant playing in the machine), then when the final procedure was settled on they ran the test for 2,000,000 keystrokes (after I came home - this takes about 2 weeks). We tested different cloths, glues, pins and fitting procedures, and found that the _fitting procedures_ had the most impact on the stability of the action center fit. All the cloths and glues exhibited the same symptoms of tightening under use, to varying degrees, when fit only by shrink fitting, or wet sizing. Lubrication of the parts helped this, but didn't solve the problem. We tested a variety of lubricants, everything I know of except Steinway's Emralon dip. We tried to map the movement of the fibers by noting their locations before and after under a microscope. Although super precise movement mapping of every visible fiber wasn't practical, it was clear that the fibers in wet-sized bushings would move around and change position after being played. In the more stable, burnished bushings the fibers hardly moved at all. Another interesting point - once the fibers move around and start to bind on the pin, the wool wears very clear grooves into the pin. The wool fibers leave what look like impressions around the circumference. The only procedure that was 100% reliable in the factory was reaming and/or burnishing to achieve the final fit. While centers that were wet-fit only, using the best combination of shrinking solution lubricant and procedure, tightened up an average of 2.5 grams (range: .5 - 5 grams) after 200,000 keystrokes, the reamed flanges _loosened_ an average of .5 grams. Unfortunately the problem with reaming is that the flange can become spongy and soft, so wet fitting combined with burnishing was settled on as the best procedure. The more rough the surface of the reaming tool, the more the center will loosen up with use. The best broaches have only slight roughness, and the burnishing / smoothing step after reaming is important for keeping the fit stable. Another variable that contributes to loosening is the quality of the cloth - cheap cloth tends to loosen up more after reaming than good, close weave, high density cloth. If you work a well-reamed part _really_ hard you can usually get it to loosen a little - maybe .5 to 1 gram looser than right after pinning. Part of this is from the wool fibers being bent into unhappy positions when the new pin was inserted, and part of it is the inevitable fluffiness of the surface fibers contacting the pin, which become packed down during use. The only solution is to test for loosening when you establish your procedure on the first few parts in the set, and adjusting the procedure to minimize the loosening. Try changing to the broach of the same size as the pin you are going to use, or even the broach that is .001 larger than the pin, with only 1 pass of the rough part of the broach and a few seconds of vigorous burnishing. This will improve the stability of the fit. Another thing you can try is to wet size the cloth first with a pin .002" smaller than the final pin, then do the broach work. Don_Mannino@yca.ccmail.compuserve.com
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