It's an 1885 John Broadwood & Sons 6' 6" grand. Starts from an octave either end. The warp is approx. 1cm. Any suggestions?

I can tell you what not to do - don't apply steam and weights in an attempt to warp it back - doesn't work!!!! How about planing the bottom of the key frame or adding shims to it so it matches the key bed??

Thanks Bob

Would you suggest using leather or wood shims? I just don't know about planing the key frame as it sounds somewhat irreversible.

Take off the action and keys, saw kerfs 3 into the keyframe one on top side and 2 under then fill the underside kerfs with wedges. As to where to make the kerfs you need to be a little more descriptive. Is the warp on the front rail (batt pin) or does it extend to the balance rail? If the keyframe is just place in, on the keybed and you tap it, where does it knock?

Basicly it wont be solved in two minutes but hope this gives you some data. Also, are the cheek blocks not doing anything?

Brian,

Thanks for the reply and your suggestions, you speak of sawing kerfs on the top (sorry but not sure what you mean). The warp runs from the FT rail through to the BT rail and at the worst point covers the middle two octaves with a gap of 1cm, gradually diminishing (uniform) towards the end blocks. The idea of wedges is a good one, but please extrapolate on the use of wedges on the top of the rail, as this eludes me.
There is also a una corda so should the wedges be made of pine or beech? And how many wedges would you suggest?

A kerf is a saw cut, check it in the dictionary. I'm sure you must have seen such in other keyframes? One you leave open - on top, two below and either side of the one on top you wedge (with a hardwood)to force it to unbow. Although as you decribe a large bowing you may need several deep kerfs in the front and balance rail. An another thing, when you take the action stack off does the bow increase?

What about inserting hardwood along the length of the keybed at FT, BR, & BT areas?
When the action is extracted there isn't any evidence that the warp is unstable but constant.