Concerning Dags and the Return Spring:
First, consider the dag at the back of the keybed (pronounced dog, as in bench dog, thank you David Hughes). Blue painter's tape (useful for not leaving a residue when removed) secures front punchings cut to fit vertically under the overhang and selected to stop the action at the same spot as the cheekblocks. Cheekblocks can be heavy and hard work, or just annoying and a case hazard, but shimmed dags make the repeated, same-place action return we need for this work easy and cheekblock-free.
Later, with shims off, the dags won't mind a tweaked action positioning at the cheekblock. Slight shifts in or out will have sufficient dag clearance and will not affect keyframe bedding. Some dags do have a screw to position the action, and a few try to play holddown, but for the rest, stopping and holding down are loose-fitting functions:
- for when the action slides in (so it doesn't collide with belly rail or damper system) and
- for when the piano is on its side (so the action doesn't fall against pinblock, plate, or dampers).
Okay, but why am I removing the return spring?
If its contact areas are not vertical or if they have a burr, or if they have just strongly pressed in the same spot for a very long time, they may have left indentations in the side of the keyframe or a groove (particularly with older, mahogany-sided keyframes). And if so, the treble end of the keyframe will be vertically locked and not conducive to fine adjustments. Even a perfectly installed spring will complicate making bedding adjustments with its pressure and friction further stiffening the two stiffest parts of the keyframe.
It only takes a couple of minutes to remove the spring, tape screws in place, and draw an up-arrow to guarantee all goes back in correctly. Then, this neat package can be stored on the plate or elsewhere for post-regulation reinsertion.
Without spring removal, the keyframe we sample and the keyframe we set up on the bench may have different tensions, and slightly different shapes, jeopardizing the usefulness of all subsequent steps!
When the spring goes back in at the end of the regulation, shim it to be vertical with front punchings. If the spring is twisted, untwist it with a small wrench or other device with good leverage (the fork style upright spoon-bending tool works pretty well). Strategic placement of punchings between spring and case side can also accomplish this, but without trying to affect a permanent bend in the spring.
And, of course, before you're through, sand vertically flat the treble spring-bearing surface of the keyframe and spot-validate your bedding and regulation.
Next week: Shape of the Keybed.