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Step 4Keyframe
The keyframe can be rectangular, trapezoidal or even have no parallel sides depending on the spacing of keys and the strings and the angle of the hammers, and so the lengths of the rails and stretchers vary depending on the design of a specific piano.
My keyframe rails are made of cherry, and they are connected with mahogany stretchers. The front rail is 7.5cm wide and 14.5mm thick. The blank was longer than 60cm, a little wider than the finished keyplank.
The backrail is 8.5cm wide and 11.5mm thick, and the blank was more than 57cm long. It has a rabbet at the back edge, bevelled to 5mm at its thinnest, to fit similarly tapered blocks at the back of the keywell, but this is only useful in squares and grands.
The balance rail is 4cm wide, a little short of 2cm tall and at started more than 50cm long.
The side stretchers are 9mm mahogany planks, about 6cm wide. The treble stretcher is longest and is about 40cm long. They are quartersawn, but the grain was so interlocked they were more difficult to make than if they were flatsawn.
The stretchers are joined with the rails with open mortises and tenons with the tenons cut on the stretchers. I marked the mortises out by laying the rails on top of the stretchers on a pattern marked on my work table, cut nicks at their intersections with a knife and transferred them all around with a square and protractor. I marked the widths of the mortises and tenons with a marking gauge.
I cut the mortises with a fence on the bandsaw. I chopped out the waste with a narrow chisel and finished the sides and bottom with something like a plane-makers float which is a kind of thick hand saw with no set. I cut the tenons the same way and slightly too thick so I could plane each one to fit, and when they all fit I assembled it so I could mark and trimmed all the shoulders so they were flush. When the outside stretchers fit I marked for the middle stretcher, disassembled the frame and cut shallow mortises in each of the rails, and then cut tenons on the stretcher.
After fitting the middle stretcher I glued the keyframe together, making sure it was square and flat, and clamped each of the corner joints together to prevent the moisture from the glue from pulling the pieces apart. Once it was dry I planed the obvious high spots, and checked it on a flat table - it didn't take much to make it but it's not so important in a square or upright where it's screwed down. In a grand it might be better to have the sides higher.
Finally I marked for the balance rail and rabetted it on the bottom to slip over the stretchers. I only fastened it with countersunk screws so I could remove it to bevel it. This also helps regulating when it's finished.
My keyframe rails are made of cherry, and they are connected with mahogany stretchers. The front rail is 7.5cm wide and 14.5mm thick. The blank was longer than 60cm, a little wider than the finished keyplank.
The backrail is 8.5cm wide and 11.5mm thick, and the blank was more than 57cm long. It has a rabbet at the back edge, bevelled to 5mm at its thinnest, to fit similarly tapered blocks at the back of the keywell, but this is only useful in squares and grands.
The balance rail is 4cm wide, a little short of 2cm tall and at started more than 50cm long.
The side stretchers are 9mm mahogany planks, about 6cm wide. The treble stretcher is longest and is about 40cm long. They are quartersawn, but the grain was so interlocked they were more difficult to make than if they were flatsawn.
The stretchers are joined with the rails with open mortises and tenons with the tenons cut on the stretchers. I marked the mortises out by laying the rails on top of the stretchers on a pattern marked on my work table, cut nicks at their intersections with a knife and transferred them all around with a square and protractor. I marked the widths of the mortises and tenons with a marking gauge.
I cut the mortises with a fence on the bandsaw. I chopped out the waste with a narrow chisel and finished the sides and bottom with something like a plane-makers float which is a kind of thick hand saw with no set. I cut the tenons the same way and slightly too thick so I could plane each one to fit, and when they all fit I assembled it so I could mark and trimmed all the shoulders so they were flush. When the outside stretchers fit I marked for the middle stretcher, disassembled the frame and cut shallow mortises in each of the rails, and then cut tenons on the stretcher.
After fitting the middle stretcher I glued the keyframe together, making sure it was square and flat, and clamped each of the corner joints together to prevent the moisture from the glue from pulling the pieces apart. Once it was dry I planed the obvious high spots, and checked it on a flat table - it didn't take much to make it but it's not so important in a square or upright where it's screwed down. In a grand it might be better to have the sides higher.
Finally I marked for the balance rail and rabetted it on the bottom to slip over the stretchers. I only fastened it with countersunk screws so I could remove it to bevel it. This also helps regulating when it's finished.
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