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I’ve heard this one before and I’m not sure just where it comes from. No truth to it as far as I know. There are some old frames that break rather easily but that is the result of the weak alloy from which the frame was cast, not because of any deterioration in the metal over time.



The frame is not bowing on its own. The piano was either built that way because that is the shape of the frame as it came from the foundry and they didn’t bother to pull it down or tensile stress from the strings is pulling the frame forward. Probably the former.



If it is making you nervous why not just check to make sure the screws are not stripped and leave it alone?

ddf

General question...is there any danger in tightening plate bolts when the piano is fully strung and pretty much up to pitch?

Yup! It can crack the plate, or stress it enough that it'll crack after you are safely out of the door-yard. The latter is preferable.

Thanks Del

Yes, there are circumstances under which this can happen although the pitch of the piano will have nothing to do with why the frame might break.

Picture the following scenario:
As the piano is being built the frame is warped from the foundry. It fits flush against the pinblock (part of the skeleton, or back assembly) but stands proud along the top edge. Tuning pin bushings are inserted and the piano is strung. During stringing the tuning pin bushings are driven solidly against the pinblock surface and are captured firmly between the tuning pin and the holes in the frame. From here on the tuning pin bushings are holding the frame away from the pinblock surface.

Now picture the technician coming along and spotting this gap and trying to “fix” it by tightening the screws along the top edge of the frame. This will start to draw the frame tight against the pinblock surface but down where the tuning pin bushings are located the frame cannot move. There will be an abnormal bending stress created between the tuning pin field and the top edge of the frame. If this bending stress becomes great enough I can see where a crack might develop between the tuning pin field and the top edge of the frame.

This is why I made my earlier comment:


I don’t like seeing those gaps and, like Ryan, I try to draw them in when I can. If it doesn’t draw in readily I’m not going to force the issue. I’ve not yet tried filling the gap with epoxy but, done neatly, this would resolve the aesthetic issue. If the frame is drawing away from the pinblock due to tensile stress it should draw in fairly easily.

ddf

Having been around alot of old uprights that havn't heard a tuners footsteps much less been tuned in thirty odd years I always check the plate bolts and screws before I tune the first note. I agree in part that tightening a plate thats up to pitch could crack it but not tightening the screws at least some could result in the same. For whatever reason I often find the top bolts are at least a quarter turn loose and even one that is stripped or nearly so. I don't try to tighten it if the plate is obviously moved out from the pinblock area or if I do relieve the tension as Del has implied.

Theres my 2 cents now I feel better!

-Daniel

That's what I thought Del.....thanks for the explanation.....I tightened the plate bolts once on a 1920's player grand...less than an 1/4 inch turn all around..as soon as I did that, the sound improved immensely, so much so, I almost did not sell it!!!..but...I said if a little is good, more is better...wrong!.....as soon as I tightened them a bit more...that great sound was GONE.....the people that bought it were happy with the sound....for my ears, it had lost the beauty of the sound. I was lucky I did not crack the plate!