The same basic bedding strategy will work for both stiff and flexible keyframes. Whatever the starting point, once one glidebolt connects with keybed, bed the rest neighbor-by-neighbor advancing and retreating each to touch then just barely touch, monitoring as it lifts and lowers the previously bedded stud off and back onto the keybed. Have the sustain pedal fully depressed for this unless heading to the bench for regulating. The touch-downs can be tested by lightly thumping for tap/no-tap or by the dial indicating of a WNG Keyframe Bedding Tool. With both stiff and flexible situations, I start in the bass since there lies the greatest part of the action's load and the part least easily unseated as subsequent studs touch down. There are edge case keyframes where the strategy may have to work a little differently and there is the common situation where there's no time for spring removal, etc. Symptoms must be solved and resolved quickly. Here, the same principles apply but they must adapt to priorities of the moment.
Let's consider the time-pinched case first. Constraints might be of budget or deadline or instructions from an employer. Or we may hesitate to venture beyond a well-practiced comfort zone. Whatever the constraints, the fastest, most direct route dictates. The extra friction and stiffness near the lowest and highest glidebolts must become assets. In the bass, we can refresh keyframe-to-stoprail contact each time before testing. But there is no relieving the return spring friction and stiffness in the high treble. And the spring may be embedded. Rather than fight this, start by tweaking the top stud to make it a locked-in, no-symptom asset (make sure all other accessible studs are backed off keybed first). Then, whether stiff or flexible, go back to the bass end and proceed using the look-back-and-then-validate method previously described. For the flexible keyframe, this will be adjusting stud #1 while checking hidden stud #2 with sustain pedal engaged. Use soft-pedal to clarify. In the stiff keyframe, sustain pedal depressed, bed stud #2 first, checking that it doesn't upset backrail or frontrail. Now, adjust #1 to unseat and reseat #2, and proceed with sustain and soft pedals to seat and refine each remaining stud.
If this is all it takes, Chris, why have you taken us way round the houses to get here? You may be ready to leave the piano noise-free with this method but not ready for a bench regulation that will fit back in the piano. When faced with action rebuilding, restoring, or regulating, the bench offers back-and-eye-friendly efficiencies that are significant. The more thorough, spring-free approach can guarantee success, whereas the spring-loaded result obscures details that can contribute to accumulated error on the bench or small imbalances in the piano that show up later in playing. And fanciest regulation tooling can be foiled by such details leading to otherwise unnecessary rework.
A couple of edge cases are worth noting: the stiff keyframe with inaccessible studs and one with studs from keybed to support frontrail. Both of these will benefit from having the action fully assembled, spring out, and cheekblocks adjusted. For a stiff action with inaccessible studs, back the accessible studs up and see if those that remain sit on the keybed (check with and without pedal). If they do, treat them as if they were the hidden studs of a flexible keyframe and use the looking back method to fill in remaining studs while not unseating initial ones. If one or more do not touch, key removal is in the cards.
The Mason & Hamlin A action shown in the lead photo has two studs in the treble that need key removal to be adjusted. If they both touch the keybed with pedal engaged, the fully-assembled flexible-keyframe strategy can apply. It is slightly more difficult going from light end to heavy but has the same advantages of all assembled-action bedding: these are the real weights and influences and less time will be consumed.
Bedding a frontrail with studs supporting from the keybed is a little different. Here, key pin fit in front mortises determines the rail's elevation, that and enough space for all needed adjustments. Make sure accessible balancerail studs are backed up first. At least one frontrail stud must support the agreed-upon height and then each next stud can do the unseat and reseat trick until all share the support and none tap with or without pedals.
Another more radical edge case is the studless keyframe that doesn't fit. If much money is being invested in the rest of the piano, a poorly fitting keyframe should not be an option. Maple can be added to back or front rail and pieces placed where studs would go if there were studs. I have employed such techniques with success - but only under duress. Consider case part fit and action elevations to choose the best solution. If you have such a situation, feel free to call me for a strategy chat.
In the end, as with a good tuner being able to start from any note, a good regulator can bed from any stud. But also, as with tuning, good strategy helps and whatever the order of operations, good results speak for themselves.
Next time: New Hammers for the Mason