KS 5: Bedding the Cheekblocks

KS 5: Bedding the Cheekblocks

What are the functions of a cheekblock? In a Steinway grand, a cheekblock provides three important services: positioning the action in-and-out for tone, side-to-side for soft-pedal shifting, and up-and-down to complete the crowned frontrail bedding. Arguably, there is a fourth function: securing action to keybed for when the piano goes on its side. And, of course, there are the casepart functions to hold and stop the fallboard. In any case, the guiding and holddown functions conflict, with downward pressure on pins that must slide freely and silently side-to-side.

The Steinway factory minimizes the negatives of this conflict by first creating cheekblock bracket downbearing on the keyframe guide pins, then easing that to its best place with under-cheekblock shims. Many of us who have regulated older Steinway grands are familiar with removing factory shims to refresh the frontrail holddown function, worn loose as the crowned fit pressed brass against steel and the shift pedal rubbed that friction back and forth. In very old Steinways, shimming the brackets down a little might also be needed.

Years ago, as part of my Regulation Station delivery to a university, I gave a presentation to the local PTG chapter in the evening and followed up the next day with a training session for the university tech. My demonstrations were on a 6-month-old Steinway B, whose bedding I validated before class. And that class, showing the chapter my bedding and sampling procedures, went well. 

But the next day, I experienced an embarrassing chasing-of-my-tail in the setup training session and eventually had to back up to see where I went wrong. Right at the beginning of the Bedding Protocol, where it said "bed the cheekblocks", I had skipped ahead to save time. With no symptom from the frontrail and no looseness at the cheekblocks, it seemed reasonable, never occurring to me that they might be too tight.

So, I devised a simple test to find out if that might be the case. By placing a white frontrail punching under each cheekblock and securing them, each end of the sprung frontrail should have produced a little tap when tapped. But they didn't. In the end, one side needed blue and the other red. That's .010" and .007" worth of extra downbearing that the punchings relieved, relaxing tensions in the action enough to allow the in-piano sampling to work on the bench. 

Once there is no play between frontrail and keybed, there is no direct way to know if there is more downbearing than needed. If the white punching test does not produce a tap, then try thicker punchings until one does, then back up a size. Bearing will now be sufficient, with extra bearing minimized.

A version of this procedure for full-fitting frontrails can make sure their guide pins have no downward cheekblock pressure but a minimal gap between brackets and pins. Place a punching between frontrail and keybed back far enough and just thick enough to create a tap at the end of the frontrail. Then shim the cheekblock just enough to retain the slightest tap.

When done, glue added punchings to the original shims or to where they would have been at the front underside of the cheekblocks. Use two punchings side-by-side for wide cheekblocks. If there is need to check and tweak the fit for concerts in different seasons, you can leave the punchings unglued. But this assumes that the next technician will know what the punchings are there for, notice if they fall out, and know how to choose what to put back in. Generally, gluing them in, like Steinway does, is a good idea.

Next week: Hidden Glidebolts

(Index of all articles in this series)


Jim F Anderson

Always on the mark!

Jim F Anderson
Mike Dugan

Marvelous information and tips!

Mike Dugan

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